Re: [RFC] media DT bindings

Re: [RFC] media DT bindings

[Sylwester Nawrocki]

Hi,

Cc: devicetree-disscuss@lists.ozlabs.org

On 07/11/2012 04:27 PM, Guennadi Liakhovetski wrote:
> Hi all
> 
> Background
> ==========
> 
> With ARM adoption of flat Device Trees a need arises to move platform
> device descriptions and their data from platform files to DT. This has
> also to be done for media devices, e.g., video capture and output
> interfaces, data processing devices, camera sensors, TV decoders and
> encoders. This RFC is trying to spawn a discussion to define standard V4L
> DT bindings. The first version will concentrate on the capture path,
> mostly taking care of simple capture-interface - camera sensor / TV
> decoder configurations. Since the author is not working intensively yet
> with the Media Controller API, pad-level configuration, these topics might
> be underrepresented in this RFC. I hope others, actively working in these
> areas, will fill me in on them.

We've done some work on device tree support for SoC camera interface
with driver based on the Media Controller API, I've posted some RFC
patches a few weeks ago:
http://www.mail-archive.com/devicetree-discuss@lists.ozlabs.org/msg14769.html
But unfortunately didn't receive any comments, perhaps because the actual
bindings were not abstracted enough from a specific hardware support.
An updated version of these patch set can be found here:
https://github.com/snawrocki/linux/commits/camera-of-2

Of course we shouldn't be forgetting that underlying bindings need to 
be the same, regardless of the drivers are based on soc_camera, Media 
Controller/subdev pad-level frameworks, or something else. Anything 
linux specific in the bindings would be inappropriate.

> Overview
> ========
> 
> As mentioned above, typical configurations, that we'll be dealing with
> consist of a DMA data capture engine, one or more data sources like camera
> sensors, possibly some data processing units. Data capture and processing
> engines are usually platform devices, whereas data source devices are
> typically I2C slaves. Apart from defining each device we'll also describe
> connections between them as well as properties of those connections.
> 
> Capture devices
> ==============================
> 
> These are usually platform devices, integrated into respective SoCs. There
> also exist external image processing devices, but they are rare. Obvious
> differences between them and integrated devices include a different bus
> attribution and a need to explicitly describe the connection to the SoC.
> As far as capture devices are concerned, their configuration will
> typically include a few device-specific bindings, as well as standard
> ones. Standard bindings will include the usual "reg," "interrupts,"
> "clock-frequency" properties.
> 
> It is more complex to describe external links. We need to describe
> configurations, used with various devices, attached to various pads. It is
> proposed to describe such links as child nodes. Each such link will
> reference a client pad, a local pad and specify the bus configuration. The
> media bus can be either parallel or serial, e.g., MIPI CSI-2. It is
> proposed to describe both the bus-width in the parallel case and the
> number of lanes in the serial case, using the standard "bus-width"
> property.
> 
> On the parallel bus common properties include signal polarities, possibly
> data line shift (8 if lines 15:8 are used, 2 if 9:2, and 0 if lines 7:0),
> protocol (e.g., BT.656). Additionally device-specific properties can be
> defined.
> 
> A MIPI CSI-2 bus common properties would include, apart from the number of
> lanes, routed to that client, the clock frequency, a channel number,
> possibly CRC and ECC flags.
> 
> An sh-mobile CEU DT node could look like
> 
> 	ceu0@0xfe910000 = {
> 		compatible = "renesas,sh-mobile-ceu";
> 		reg =<0xfe910000 0xa0>;
> 		interrupts =<0x880>;
> 		bus-width =<16>;		/* #lines routed on the board */
> 		clock-frequency =<50000000>;	/* max clock */
> 		#address-cells =<1>;
> 		#size-cells =<0>;
> 		...
> 		ov772x-1 = {
> 			reg =<0>;
> 			client =<&ov772x@0x21-0>;
> 			local-pad = "parallel-sink";
> 			remote-pad = "parallel-source";

I'm not sure I like that. Is it really needed when we already have
the child/parent properties around ?

> 			bus-width =<8>;	/* used data lines */
> 			data-shift =<0>;	/* lines 7:0 are used */
> 			hsync-active =<1>;	/* active high */
> 			vsync-active =<1>;	/* active high */

In the end I took a bit different approach, similar to how the interrupt 
flag bindings are defined:
https://github.com/snawrocki/linux/commit/c17a61a07008eeb8faea0205f7cc440545641adb

However using a separate boolean for each signal, as you proposed, might 
not be that much of string parsing, and it would have hurt less if this 
would have been done is some common helper modules.

> 			pclk-sample =<1>;	/* rising */
> 			clock-frequency =<24000000>;
> 		};
> 	};
> 
> Client devices
> ==============
> 
> Client nodes are children on their respective busses, e.g., i2c. This
> placement leads to these devices being possibly probed before respective
> host interfaces, which will fail due to known reasons. Therefore client
> drivers have to be adapted to request a delayed probing, as long as the
> respective video host hasn't probed.

I doubt this is going to be sufficient. Video bridge drivers may require
all their sub-devices (e.g. I2C client devices) to be registered, in order
to complete their probing. This was discussed in the past:
http://www.mail-archive.com/devicetree-discuss@lists.ozlabs.org/msg06595.html

So we ended up with defining an aggregate DT node that happens to be
associated with the camera media device driver.

Here is an example of how it might look like:
https://github.com/snawrocki/linux/commit/eae639132681df6c068dc869bb8973f8d9d3efa1

> Client nodes will include all the properties, usual for their busses.
> Additionally they will specify properties private to this device type and
> common for all V4L2 client devices - device global and per-link. I think,

Sounds good.

> we should make it possible to define client devices, that can at run-time
> be connected to different sinks, even though such configurations might not
> be very frequent. To achieve this we also specify link information in
> child devices, similar to those in host nodes above. This also helps
> uniformity and will let us implement and use a universal link-binding
> parser. So, a node, that has been referenced above could look like

It seems dubious to me to push media links' description into DT. Links can 
be configurable, and I don't think it's a rare situation. I'm inclined to
code the interconnections within a composite device driver.

> 
> 	ov772x@0x21-0 = {
> 		compatible = "omnivision,ov772x";
> 		reg =<0x21>;
> 		vdd-supply =<&regulator>;
> 		bus-width =<10>;
> 		#address-cells =<1>;
> 		#size-cells =<0>;
> 		...
> 		ceu0-1 = {
> 			reg =<0>;
> 			media-parent =<&ceu0@0xfe910000>;
> 			bus-width =<8>;
> 			hsync-active =<1>;
> 			vsync-active =<0>;	/* who came up with an inverter here?... */
> 			pclk-sample =<1>;
> 		};

Are these mostly supposed to be properties specific to a sub-device and
used by a host ?

If so, how about adding them under the host or the aggregate node grouped
into a sub-device specific child node ?

> 	};
> 
> Data processors
> ===============
> 
> Data processing modules include resizers, codecs, rotators, serialisers,
> etc. A node for an sh-mobile CSI-2 subdevice could look like
> 
> 	csi2@0xffc90000 = {
> 		compatible = "renesas,sh-mobile-csi2";
> 		reg =<0xffc90000 0x1000>;
> 		interrupts =<0x17a0>;
> 		bus-width =<4>;
> 		clock-frequency =<30000000>;
> 		...
> 		imx074-1 = {
> 			client =<&imx074@0x1a-0>;
> 			local-pad = "csi2-sink";
> 			remote-pad = "csi2-source";
> 			bus-width =<2>;
> 			clock-frequency =<25000000>;
> 			csi2-crc;
> 			csi2-ecc;
> 			sh-csi2,phy =<0>;
> 		};
> 		ceu0 = {
> 			media-parent =<&ceu0@0xfe910000>;
> 			immutable;

> 		};
> 	};
> 
> The respective child binding in the CEU node could then look like
> 
> 		csi2-1 = {
> 			reg =<1>;
> 			client =<&csi2@0xffc90000>;
> 			immutable;
> 		};

It look a bit complex, and could more complex when we run into a system
supporting more complex interconnections. I would prefer some sort of
more flat structure...

> Comments welcome.
> 
> Thanks
> Guennadi
> ---
> Guennadi Liakhovetski, Ph.D.
> Freelance Open-Source Software Developer
> http://www.open-technology.de/

--

Thanks,
Sylwester

Re: [RFC] media DT bindings

[Guennadi Liakhovetski]

Hi Sylwester

Thanks for your comments.

On Fri, 13 Jul 2012, Sylwester Nawrocki wrote:

> Hi,
> 
> Cc: devicetree-disscuss@lists.ozlabs.org
> 
> On 07/11/2012 04:27 PM, Guennadi Liakhovetski wrote:
> > Hi all
> > 
> > Background
> > ==========
> > 
> > With ARM adoption of flat Device Trees a need arises to move platform
> > device descriptions and their data from platform files to DT. This has
> > also to be done for media devices, e.g., video capture and output
> > interfaces, data processing devices, camera sensors, TV decoders and
> > encoders. This RFC is trying to spawn a discussion to define standard V4L
> > DT bindings. The first version will concentrate on the capture path,
> > mostly taking care of simple capture-interface - camera sensor / TV
> > decoder configurations. Since the author is not working intensively yet
> > with the Media Controller API, pad-level configuration, these topics might
> > be underrepresented in this RFC. I hope others, actively working in these
> > areas, will fill me in on them.
> 
> We've done some work on device tree support for SoC camera interface
> with driver based on the Media Controller API, I've posted some RFC
> patches a few weeks ago:
> http://www.mail-archive.com/devicetree-discuss@lists.ozlabs.org/msg14769.html
> But unfortunately didn't receive any comments,

You have now ;-)

> perhaps because the actual
> bindings were not abstracted enough from a specific hardware support.
> An updated version of these patch set can be found here:
> https://github.com/snawrocki/linux/commits/camera-of-2
> 
> Of course we shouldn't be forgetting that underlying bindings need to 
> be the same, regardless of the drivers are based on soc_camera, Media 
> Controller/subdev pad-level frameworks, or something else.

Of course, the more properties are common - the better. I also made sure 
not to introduce any soc-camera specific properties. But since I mostly 
work with those systems, I am not fully aware of requirements, imposed by 
other hardware types, so, I hope others will contribute to this work:-)

> Anything linux specific in the bindings would be inappropriate.

Not sure what you mean here - which Linux specific bindings and why they 
wouldn't be appropriate? Don't think our bindings would be used by any 
other OS kernels.

> > Overview
> > ========
> > 
> > As mentioned above, typical configurations, that we'll be dealing with
> > consist of a DMA data capture engine, one or more data sources like camera
> > sensors, possibly some data processing units. Data capture and processing
> > engines are usually platform devices, whereas data source devices are
> > typically I2C slaves. Apart from defining each device we'll also describe
> > connections between them as well as properties of those connections.
> > 
> > Capture devices
> > ==============================
> > 
> > These are usually platform devices, integrated into respective SoCs. There
> > also exist external image processing devices, but they are rare. Obvious
> > differences between them and integrated devices include a different bus
> > attribution and a need to explicitly describe the connection to the SoC.
> > As far as capture devices are concerned, their configuration will
> > typically include a few device-specific bindings, as well as standard
> > ones. Standard bindings will include the usual "reg," "interrupts,"
> > "clock-frequency" properties.
> > 
> > It is more complex to describe external links. We need to describe
> > configurations, used with various devices, attached to various pads. It is
> > proposed to describe such links as child nodes. Each such link will
> > reference a client pad, a local pad and specify the bus configuration. The
> > media bus can be either parallel or serial, e.g., MIPI CSI-2. It is
> > proposed to describe both the bus-width in the parallel case and the
> > number of lanes in the serial case, using the standard "bus-width"
> > property.
> > 
> > On the parallel bus common properties include signal polarities, possibly
> > data line shift (8 if lines 15:8 are used, 2 if 9:2, and 0 if lines 7:0),
> > protocol (e.g., BT.656). Additionally device-specific properties can be
> > defined.
> > 
> > A MIPI CSI-2 bus common properties would include, apart from the number of
> > lanes, routed to that client, the clock frequency, a channel number,
> > possibly CRC and ECC flags.
> > 
> > An sh-mobile CEU DT node could look like
> > 
> > 	ceu0@0xfe910000 = {
> > 		compatible = "renesas,sh-mobile-ceu";
> > 		reg =<0xfe910000 0xa0>;
> > 		interrupts =<0x880>;
> > 		bus-width =<16>;		/* #lines routed on the board */
> > 		clock-frequency =<50000000>;	/* max clock */
> > 		#address-cells =<1>;
> > 		#size-cells =<0>;
> > 		...
> > 		ov772x-1 = {
> > 			reg =<0>;
> > 			client =<&ov772x@0x21-0>;
> > 			local-pad = "parallel-sink";
> > 			remote-pad = "parallel-source";
> 
> I'm not sure I like that. Is it really needed when we already have
> the child/parent properties around ?

I think it is. Both the host and the client can have multiple pads (e.g., 
parallel / serial). These properties specify which pads are used and make 
the translation between DT data and our subdev / pad APIs simpler.

> > 			bus-width =<8>;	/* used data lines */
> > 			data-shift =<0>;	/* lines 7:0 are used */
> > 			hsync-active =<1>;	/* active high */
> > 			vsync-active =<1>;	/* active high */
> 
> In the end I took a bit different approach, similar to how the interrupt 
> flag bindings are defined:
> https://github.com/snawrocki/linux/commit/c17a61a07008eeb8faea0205f7cc440545641adb
> 
> However using a separate boolean for each signal, as you proposed, might 
> not be that much of string parsing, and it would have hurt less if this 
> would have been done is some common helper modules.

Personally, I think, I would prefer to have 1 property per flag. Whether 
we use an integer as above or a boolean as in this patch:

http://thread.gmane.org/gmane.linux.drivers.devicetree/17495

can be discussed.

> > 			pclk-sample =<1>;	/* rising */
> > 			clock-frequency =<24000000>;
> > 		};
> > 	};
> > 
> > Client devices
> > ==============
> > 
> > Client nodes are children on their respective busses, e.g., i2c. This
> > placement leads to these devices being possibly probed before respective
> > host interfaces, which will fail due to known reasons. Therefore client
> > drivers have to be adapted to request a delayed probing, as long as the
> > respective video host hasn't probed.
> 
> I doubt this is going to be sufficient. Video bridge drivers may require
> all their sub-devices (e.g. I2C client devices) to be registered, in order
> to complete their probing. This was discussed in the past:
> http://www.mail-archive.com/devicetree-discuss@lists.ozlabs.org/msg06595.html

How about this:

 - if sensors get probed before the host, they request deferred probing;
 - when the host gets probed, it checks, which clients it should be 
   getting, enables respective clocks, registers a notifier on respective 
   busses (&i2c_bus_type for I2C) and returns success
 - when after this sensors are re-probed, the notifier gets called and the 
   host can complete its initialisation

> So we ended up with defining an aggregate DT node that happens to be
> associated with the camera media device driver.
> 
> Here is an example of how it might look like:
> https://github.com/snawrocki/linux/commit/eae639132681df6c068dc869bb8973f8d9d3efa1

Yeah, it can be done if absolutely needed, but I wouldn't make it 
mandatory. On simpler sistems 1 host and 1 sensor nodes should suffice.

> > Client nodes will include all the properties, usual for their busses.
> > Additionally they will specify properties private to this device type and
> > common for all V4L2 client devices - device global and per-link. I think,
> 
> Sounds good.
> 
> > we should make it possible to define client devices, that can at run-time
> > be connected to different sinks, even though such configurations might not
> > be very frequent. To achieve this we also specify link information in
> > child devices, similar to those in host nodes above. This also helps
> > uniformity and will let us implement and use a universal link-binding
> > parser. So, a node, that has been referenced above could look like
> 
> It seems dubious to me to push media links' description into DT. Links can 
> be configurable, and I don't think it's a rare situation. I'm inclined to
> code the interconnections within a composite device driver.

Shouldn't a list of all possible links be provided by the platform? If a 
certain pad can participate in several links, all of them should be 
specified and at run-time we just switch between them?

> > 	ov772x@0x21-0 = {
> > 		compatible = "omnivision,ov772x";
> > 		reg =<0x21>;
> > 		vdd-supply =<&regulator>;
> > 		bus-width =<10>;
> > 		#address-cells =<1>;
> > 		#size-cells =<0>;
> > 		...
> > 		ceu0-1 = {
> > 			reg =<0>;
> > 			media-parent =<&ceu0@0xfe910000>;
> > 			bus-width =<8>;
> > 			hsync-active =<1>;
> > 			vsync-active =<0>;	/* who came up with an inverter here?... */
> > 			pclk-sample =<1>;
> > 		};
> 
> Are these mostly supposed to be properties specific to a sub-device and
> used by a host ?

These parameters specify the subdevice configuration and are also used by 
the subdevice to configure its signal polarities.

> If so, how about adding them under the host or the aggregate node grouped
> into a sub-device specific child node ?

We need 2 copies of them - for both pads, that's exactly the reason for 
the above inverter "joke."

> > 	};
> > 
> > Data processors
> > ===============
> > 
> > Data processing modules include resizers, codecs, rotators, serialisers,
> > etc. A node for an sh-mobile CSI-2 subdevice could look like
> > 
> > 	csi2@0xffc90000 = {
> > 		compatible = "renesas,sh-mobile-csi2";
> > 		reg =<0xffc90000 0x1000>;
> > 		interrupts =<0x17a0>;
> > 		bus-width =<4>;
> > 		clock-frequency =<30000000>;
> > 		...
> > 		imx074-1 = {
> > 			client =<&imx074@0x1a-0>;
> > 			local-pad = "csi2-sink";
> > 			remote-pad = "csi2-source";
> > 			bus-width =<2>;
> > 			clock-frequency =<25000000>;
> > 			csi2-crc;
> > 			csi2-ecc;
> > 			sh-csi2,phy =<0>;
> > 		};
> > 		ceu0 = {
> > 			media-parent =<&ceu0@0xfe910000>;
> > 			immutable;
> 
> > 		};
> > 	};
> > 
> > The respective child binding in the CEU node could then look like
> > 
> > 		csi2-1 = {
> > 			reg =<1>;
> > 			client =<&csi2@0xffc90000>;
> > 			immutable;
> > 		};
> 
> It look a bit complex, and could more complex when we run into a system
> supporting more complex interconnections. I would prefer some sort of
> more flat structure...

Ideas welcome:-)

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/

Re: [RFC] media DT bindings

[Sylwester Nawrocki]

Hi Guennadi,

On 07/16/2012 01:41 PM, Guennadi Liakhovetski wrote:
[...]
>> On 07/11/2012 04:27 PM, Guennadi Liakhovetski wrote:
>>> Hi all
>>>
>>> Background
>>> ==========
>>>
>>> With ARM adoption of flat Device Trees a need arises to move platform
>>> device descriptions and their data from platform files to DT. This has
>>> also to be done for media devices, e.g., video capture and output
>>> interfaces, data processing devices, camera sensors, TV decoders and
>>> encoders. This RFC is trying to spawn a discussion to define standard V4L
>>> DT bindings. The first version will concentrate on the capture path,
>>> mostly taking care of simple capture-interface - camera sensor / TV
>>> decoder configurations. Since the author is not working intensively yet
>>> with the Media Controller API, pad-level configuration, these topics might
>>> be underrepresented in this RFC. I hope others, actively working in these
>>> areas, will fill me in on them.
>>
>> We've done some work on device tree support for SoC camera interface
>> with driver based on the Media Controller API, I've posted some RFC
>> patches a few weeks ago:
>> http://www.mail-archive.com/devicetree-discuss@lists.ozlabs.org/msg14769.html
>> But unfortunately didn't receive any comments,
> 
> You have now ;-)

:)

>> perhaps because the actual
>> bindings were not abstracted enough from a specific hardware support.
>> An updated version of these patch set can be found here:
>> https://github.com/snawrocki/linux/commits/camera-of-2
>>
>> Of course we shouldn't be forgetting that underlying bindings need to
>> be the same, regardless of the drivers are based on soc_camera, Media
>> Controller/subdev pad-level frameworks, or something else.
> 
> Of course, the more properties are common - the better. I also made sure
> not to introduce any soc-camera specific properties. But since I mostly
> work with those systems, I am not fully aware of requirements, imposed by
> other hardware types, so, I hope others will contribute to this work:-)
> 
>> Anything linux specific in the bindings would be inappropriate.
> 
> Not sure what you mean here - which Linux specific bindings and why they
> wouldn't be appropriate? Don't think our bindings would be used by any
> other OS kernels.

The bindings should be OS agnostic, so they can be used by other operating
systems and bootloaders. That's one of fundamental FDT assumptions, AFAIU.

It is outlined in this presentation (slide 22):
http://events.linuxfoundation.org/images/stories/pdf/lf_elc12_abraham.pdf

>>> Overview
>>> ========
>>>
>>> As mentioned above, typical configurations, that we'll be dealing with
>>> consist of a DMA data capture engine, one or more data sources like camera
>>> sensors, possibly some data processing units. Data capture and processing
>>> engines are usually platform devices, whereas data source devices are
>>> typically I2C slaves. Apart from defining each device we'll also describe
>>> connections between them as well as properties of those connections.
>>>
>>> Capture devices
>>> ==============================
>>>
>>> These are usually platform devices, integrated into respective SoCs. There
>>> also exist external image processing devices, but they are rare. Obvious
>>> differences between them and integrated devices include a different bus
>>> attribution and a need to explicitly describe the connection to the SoC.
>>> As far as capture devices are concerned, their configuration will
>>> typically include a few device-specific bindings, as well as standard
>>> ones. Standard bindings will include the usual "reg," "interrupts,"
>>> "clock-frequency" properties.
>>>
>>> It is more complex to describe external links. We need to describe
>>> configurations, used with various devices, attached to various pads. It is
>>> proposed to describe such links as child nodes. Each such link will
>>> reference a client pad, a local pad and specify the bus configuration. The
>>> media bus can be either parallel or serial, e.g., MIPI CSI-2. It is
>>> proposed to describe both the bus-width in the parallel case and the
>>> number of lanes in the serial case, using the standard "bus-width"
>>> property.
>>>
>>> On the parallel bus common properties include signal polarities, possibly
>>> data line shift (8 if lines 15:8 are used, 2 if 9:2, and 0 if lines 7:0),
>>> protocol (e.g., BT.656). Additionally device-specific properties can be
>>> defined.
>>>
>>> A MIPI CSI-2 bus common properties would include, apart from the number of
>>> lanes, routed to that client, the clock frequency, a channel number,
>>> possibly CRC and ECC flags.
>>>
>>> An sh-mobile CEU DT node could look like
>>>
>>> 	ceu0@0xfe910000 = {
>>> 		compatible = "renesas,sh-mobile-ceu";
>>> 		reg =<0xfe910000 0xa0>;
>>> 		interrupts =<0x880>;
>>> 		bus-width =<16>;		/* #lines routed on the board */
>>> 		clock-frequency =<50000000>;	/* max clock */
>>> 		#address-cells =<1>;
>>> 		#size-cells =<0>;
>>> 		...
>>> 		ov772x-1 = {
>>> 			reg =<0>;

This property might be redundant, we already have the "client" phandle
pointing to "ov772x@0x21-0", which has all interesting properties inside 
it. Other than there is probably no reasonable usage for it under
"ceu0@0xfe910000" node ?

>>> 			client =<&ov772x@0x21-0>;
>>> 			local-pad = "parallel-sink";
>>> 			remote-pad = "parallel-source";
>>
>> I'm not sure I like that. Is it really needed when we already have
>> the child/parent properties around ?
> 
> I think it is. Both the host and the client can have multiple pads (e.g.,
> parallel / serial). These properties specify which pads are used and make
> the translation between DT data and our subdev / pad APIs simpler.

OK, sorry, but isn't it all about just specifying what sort of data bus 
is used ? :-)

>>> 			bus-width =<8>;	/* used data lines */
>>> 			data-shift =<0>;	/* lines 7:0 are used */
>>> 			hsync-active =<1>;	/* active high */
>>> 			vsync-active =<1>;	/* active high */
>>
>> In the end I took a bit different approach, similar to how the interrupt
>> flag bindings are defined:
>> https://github.com/snawrocki/linux/commit/c17a61a07008eeb8faea0205f7cc440545641adb
>>
>> However using a separate boolean for each signal, as you proposed, might
>> not be that much of string parsing, and it would have hurt less if this
>> would have been done is some common helper modules.
> 
> Personally, I think, I would prefer to have 1 property per flag. Whether
> we use an integer as above or a boolean as in this patch:
> 
> http://thread.gmane.org/gmane.linux.drivers.devicetree/17495
> 
> can be discussed.

I don't have strong preference, but I would vote for 
vsync/hsync/field-active-low; and pclk-sample-falling; boolean keys.

>>> 			pclk-sample =<1>;	/* rising */
>>> 			clock-frequency =<24000000>;
>>> 		};
>>> 	};
>>>
>>> Client devices
>>> ==============
>>>
>>> Client nodes are children on their respective busses, e.g., i2c. This
>>> placement leads to these devices being possibly probed before respective
>>> host interfaces, which will fail due to known reasons. Therefore client
>>> drivers have to be adapted to request a delayed probing, as long as the
>>> respective video host hasn't probed.
>>
>> I doubt this is going to be sufficient. Video bridge drivers may require
>> all their sub-devices (e.g. I2C client devices) to be registered, in order
>> to complete their probing. This was discussed in the past:
>> http://www.mail-archive.com/devicetree-discuss@lists.ozlabs.org/msg06595.html
> 
> How about this:
> 
>   - if sensors get probed before the host, they request deferred probing;
>   - when the host gets probed, it checks, which clients it should be
>     getting, enables respective clocks, registers a notifier on respective
>     busses (&i2c_bus_type for I2C) and returns success
>   - when after this sensors are re-probed, the notifier gets called and the
>     host can complete its initialisation

This could work, the sensor nodes would need to contain a reference to 
their respective media parent nodes. And of course a lot of existing
code would have to be modified to support that.

I'd like just to point one detail here, as sensor subdev drivers control
their voltage regulators and RESET/STANDBY (gpio) signals, they should
also be able to control the master clock. In order to ensure proper power 
up/down sequences. It is a bad practice to enable clocks before voltage
supplies are switched on and we shouldn't have that as a general 
assumption at the kernel frameworks.

One possible solution would be to have host/bridge drivers to register
a clkdev entry for I2C client device, so it can acquire the clock through 
just clk_get(). We would have to ensure the clock is not tried to be
accessed before it is registered by a bridge. This would require to add
clock handling code to all sensor/encoder subdev drivers though..

Or maybe we could add some capability flags, so for sensors that don't 
control the clock themselves the hosts would enable/disable it when
needed. 

>> So we ended up with defining an aggregate DT node that happens to be
>> associated with the camera media device driver.
>>
>> Here is an example of how it might look like:
>> https://github.com/snawrocki/linux/commit/eae639132681df6c068dc869bb8973f8d9d3efa1
> 
> Yeah, it can be done if absolutely needed, but I wouldn't make it
> mandatory. On simpler sistems 1 host and 1 sensor nodes should suffice.
> 
>>> Client nodes will include all the properties, usual for their busses.
>>> Additionally they will specify properties private to this device type and
>>> common for all V4L2 client devices - device global and per-link. I think,
>>
>> Sounds good.
>>
>>> we should make it possible to define client devices, that can at run-time
>>> be connected to different sinks, even though such configurations might not
>>> be very frequent. To achieve this we also specify link information in
>>> child devices, similar to those in host nodes above. This also helps
>>> uniformity and will let us implement and use a universal link-binding
>>> parser. So, a node, that has been referenced above could look like
>>
>> It seems dubious to me to push media links' description into DT. Links can
>> be configurable, and I don't think it's a rare situation. I'm inclined to
>> code the interconnections within a composite device driver.
> 
> Shouldn't a list of all possible links be provided by the platform? If a
> certain pad can participate in several links, all of them should be
> specified and at run-time we just switch between them?

Again, this could be entirely coded in drivers with minimal needed 
information retrieved from DT. Or we could have all possible link
templates in DT which would then have to be parsed/translated to 
respective user API calls. I'd like to see a real example of such 
link parsing at some driver.

>>> 	ov772x@0x21-0 = {
>>> 		compatible = "omnivision,ov772x";
>>> 		reg =<0x21>;
>>> 		vdd-supply =<&regulator>;
>>> 		bus-width =<10>;
>>> 		#address-cells =<1>;
>>> 		#size-cells =<0>;
>>> 		...
>>> 		ceu0-1 = {
>>> 			reg =<0>;
>>> 			media-parent =<&ceu0@0xfe910000>;
>>> 			bus-width =<8>;
>>> 			hsync-active =<1>;
>>> 			vsync-active =<0>;	/* who came up with an inverter here?... */
>>> 			pclk-sample =<1>;
>>> 		};

Don't we need to also specify what sort of video bus (serial/parallel)
is used in such a client node ? How the sensor sub-device driver would
determine its bus type ?

>>
>> Are these mostly supposed to be properties specific to a sub-device and
>> used by a host ?
> 
> These parameters specify the subdevice configuration and are also used by
> the subdevice to configure its signal polarities.
> 
>> If so, how about adding them under the host or the aggregate node grouped
>> into a sub-device specific child node ?
> 
> We need 2 copies of them - for both pads, that's exactly the reason for
> the above inverter "joke."

Yeah, I see. But why we need a "ceu0-1" node under "ov772x@0x21-0" node 
above ? A driver associated with ceu0@0xfe910000 node could still access 
properties at "ov772x@0x21-0" node through its "client" phandle.
I can't see an advantage of having those properties grouped into a media 
parent specific child node under the sensor node. It's not needed by the 
sensor subdev driver, is it ?

>>> 	};
>>>
>>> Data processors
>>> ===============
>>>
>>> Data processing modules include resizers, codecs, rotators, serialisers,
>>> etc. A node for an sh-mobile CSI-2 subdevice could look like
>>>
>>> 	csi2@0xffc90000 = {
>>> 		compatible = "renesas,sh-mobile-csi2";
>>> 		reg =<0xffc90000 0x1000>;
>>> 		interrupts =<0x17a0>;
>>> 		bus-width =<4>;
>>> 		clock-frequency =<30000000>;
>>> 		...
>>> 		imx074-1 = {
>>> 			client =<&imx074@0x1a-0>;
>>> 			local-pad = "csi2-sink";
>>> 			remote-pad = "csi2-source";
>>> 			bus-width =<2>;
>>> 			clock-frequency =<25000000>;
>>> 			csi2-crc;
>>> 			csi2-ecc;
>>> 			sh-csi2,phy =<0>;
>>> 		};
>>> 		ceu0 = {
>>> 			media-parent =<&ceu0@0xfe910000>;
>>> 			immutable;
>>
>>> 		};

The child nodes don't seem to have standard names. How would the csi2 
driver determine what is the purpose of each of them ?

>>> 	};
>>>
>>> The respective child binding in the CEU node could then look like
>>>
>>> 		csi2-1 = {
>>> 			reg =<1>;
>>> 			client =<&csi2@0xffc90000>;
>>> 			immutable;
>>> 		};
>>
>> It look a bit complex, and could more complex when we run into a system
>> supporting more complex interconnections. I would prefer some sort of
>> more flat structure...
> 
> Ideas welcome:-)

:) It just looked to me like a lot of parsing code for all these constructs. 
And would such design be flexible enough to support pipelines like:

[sensor] -> [MIPI-CSI2 receiver (frontend)] -> [ISP frontend (+ DMA)] -> 
[ISP (...)] -> [scaler/rotator + DMA] ->

i.e. containing more than 3 entities ?

--

Thanks,
Sylwester

Re: [RFC] media DT bindings

[Mark Brown]

On Wed, Jul 18, 2012 at 07:00:15PM +0200, Sylwester Nawrocki wrote:

> One possible solution would be to have host/bridge drivers to register
> a clkdev entry for I2C client device, so it can acquire the clock through 
> just clk_get(). We would have to ensure the clock is not tried to be
> accessed before it is registered by a bridge. This would require to add
> clock handling code to all sensor/encoder subdev drivers though..

If this is done well it could just be a simple callback, and we could
probably arrange for the framework to just implement the default
behaviour if the driver doesn't do anything explicit.

Of couse this is one of those things where we really need the generic
clock API to be generally available...

Re: [RFC] media DT bindings

[Sylwester Nawrocki]

On 07/23/2012 02:14 PM, Mark Brown wrote:
> On Wed, Jul 18, 2012 at 07:00:15PM +0200, Sylwester Nawrocki wrote:
> 
>> One possible solution would be to have host/bridge drivers to register
>> a clkdev entry for I2C client device, so it can acquire the clock through
>> just clk_get(). We would have to ensure the clock is not tried to be
>> accessed before it is registered by a bridge. This would require to add
>> clock handling code to all sensor/encoder subdev drivers though..
> 
> If this is done well it could just be a simple callback, and we could
> probably arrange for the framework to just implement the default
> behaviour if the driver doesn't do anything explicit.

I agree, if a clock is bound to a sub-device beforehand it could 
probably be done with just a callback as well. Implementing default 
behaviour at the framework makes a lot of sense too, it could ease 
the conversion process significantly.

> Of couse this is one of those things where we really need the generic
> clock API to be generally available...

Indeed, I hope it won't take too much time before at least some of the
platforms get converted.

--

Thanks,
Sylwester

Re: [RFC] media DT bindings

[Laurent Pinchart]

Hi Sylwester,

On Wednesday 18 July 2012 19:00:15 Sylwester Nawrocki wrote:
> On 07/16/2012 01:41 PM, Guennadi Liakhovetski wrote:
> [...]
> 
> >> On 07/11/2012 04:27 PM, Guennadi Liakhovetski wrote:
> >>> Hi all
> >>> 
> >>> Background
> >>> ==========
> >>> 
> >>> With ARM adoption of flat Device Trees a need arises to move platform
> >>> device descriptions and their data from platform files to DT. This has
> >>> also to be done for media devices, e.g., video capture and output
> >>> interfaces, data processing devices, camera sensors, TV decoders and
> >>> encoders. This RFC is trying to spawn a discussion to define standard
> >>> V4L DT bindings. The first version will concentrate on the capture path,
> >>> mostly taking care of simple capture-interface - camera sensor / TV
> >>> decoder configurations. Since the author is not working intensively yet
> >>> with the Media Controller API, pad-level configuration, these topics
> >>> might be underrepresented in this RFC. I hope others, actively working
> >>> in these areas, will fill me in on them.
> >> 
> >> We've done some work on device tree support for SoC camera interface
> >> with driver based on the Media Controller API, I've posted some RFC
> >> patches a few weeks ago:
> >> http://www.mail-archive.com/devicetree-discuss@lists.ozlabs.org/msg14769.
> >> html But unfortunately didn't receive any comments,
> > 
> > You have now ;-)
>
> :)
>
> >> perhaps because the actual
> >> bindings were not abstracted enough from a specific hardware support.
> >> An updated version of these patch set can be found here:
> >> https://github.com/snawrocki/linux/commits/camera-of-2
> >> 
> >> Of course we shouldn't be forgetting that underlying bindings need to
> >> be the same, regardless of the drivers are based on soc_camera, Media
> >> Controller/subdev pad-level frameworks, or something else.
> > 
> > Of course, the more properties are common - the better. I also made sure
> > not to introduce any soc-camera specific properties. But since I mostly
> > work with those systems, I am not fully aware of requirements, imposed by
> > other hardware types, so, I hope others will contribute to this work:-)
> > 
> >> Anything linux specific in the bindings would be inappropriate.
> > 
> > Not sure what you mean here - which Linux specific bindings and why they
> > wouldn't be appropriate? Don't think our bindings would be used by any
> > other OS kernels.
> 
> The bindings should be OS agnostic, so they can be used by other operating
> systems and bootloaders. That's one of fundamental FDT assumptions, AFAIU.
> 
> It is outlined in this presentation (slide 22):
> http://events.linuxfoundation.org/images/stories/pdf/lf_elc12_abraham.pdf
> 
> >>> Overview
> >>> ========
> >>> 
> >>> As mentioned above, typical configurations, that we'll be dealing with
> >>> consist of a DMA data capture engine, one or more data sources like
> >>> camera
> >>> sensors, possibly some data processing units. Data capture and
> >>> processing
> >>> engines are usually platform devices, whereas data source devices are
> >>> typically I2C slaves. Apart from defining each device we'll also
> >>> describe
> >>> connections between them as well as properties of those connections.
> >>> 
> >>> Capture devices
> >>> ==============================
> >>> 
> >>> These are usually platform devices, integrated into respective SoCs.
> >>> There also exist external image processing devices, but they are rare.
> >>> Obvious differences between them and integrated devices include a
> >>> different bus attribution and a need to explicitly describe the
> >>> connection to the SoC. As far as capture devices are concerned, their
> >>> configuration will typically include a few device-specific bindings, as
> >>> well as standard ones. Standard bindings will include the usual "reg,"
> >>> "interrupts," "clock-frequency" properties.
> >>> 
> >>> It is more complex to describe external links. We need to describe
> >>> configurations, used with various devices, attached to various pads. It
> >>> is proposed to describe such links as child nodes. Each such link will
> >>> reference a client pad, a local pad and specify the bus configuration.
> >>> The media bus can be either parallel or serial, e.g., MIPI CSI-2. It is
> >>> proposed to describe both the bus-width in the parallel case and the
> >>> number of lanes in the serial case, using the standard "bus-width"
> >>> property.
> >>> 
> >>> On the parallel bus common properties include signal polarities,
> >>> possibly data line shift (8 if lines 15:8 are used, 2 if 9:2, and 0 if
> >>> lines 7:0), protocol (e.g., BT.656). Additionally device-specific
> >>> properties can be defined.
> >>> 
> >>> A MIPI CSI-2 bus common properties would include, apart from the number
> >>> of lanes, routed to that client, the clock frequency, a channel number,
> >>> possibly CRC and ECC flags.
> >>> 
> >>> An sh-mobile CEU DT node could look like
> >>> 
> >>> 	ceu0@0xfe910000 = {
> >>> 	
> >>> 		compatible = "renesas,sh-mobile-ceu";
> >>> 		reg =<0xfe910000 0xa0>;
> >>> 		interrupts =<0x880>;
> >>> 		bus-width =<16>;		/* #lines routed on the board */
> >>> 		clock-frequency =<50000000>;	/* max clock */
> >>> 		#address-cells =<1>;
> >>> 		#size-cells =<0>;
> >>> 		...
> >>> 		ov772x-1 = {
> >>> 		
> >>> 			reg =<0>;
> 
> This property might be redundant, we already have the "client" phandle
> pointing to "ov772x@0x21-0", which has all interesting properties inside
> it. Other than there is probably no reasonable usage for it under
> "ceu0@0xfe910000" node ?
> 
> >>> 			client =<&ov772x@0x21-0>;
> >>> 			local-pad = "parallel-sink";
> >>> 			remote-pad = "parallel-source";
> >> 
> >> I'm not sure I like that. Is it really needed when we already have
> >> the child/parent properties around ?
> > 
> > I think it is. Both the host and the client can have multiple pads (e.g.,
> > parallel / serial). These properties specify which pads are used and make
> > the translation between DT data and our subdev / pad APIs simpler.
> 
> OK, sorry, but isn't it all about just specifying what sort of data bus
> is used ? :-)

In some (many/most ?) cases probably, but not in all of them.

What about merging the client and remote-pad properties ? The resulting 
property would then reference a pad with <&ov772x@0x21-0 0>.

> >>> 			bus-width =<8>;	/* used data lines */
> >>> 			data-shift =<0>;	/* lines 7:0 are used */
> >>> 			hsync-active =<1>;	/* active high */
> >>> 			vsync-active =<1>;	/* active high */
> >> 
> >> In the end I took a bit different approach, similar to how the interrupt
> >> flag bindings are defined:
> >> https://github.com/snawrocki/linux/commit/c17a61a07008eeb8faea0205f7cc440
> >> 545641adb
> >> 
> >> However using a separate boolean for each signal, as you proposed, might
> >> not be that much of string parsing, and it would have hurt less if this
> >> would have been done is some common helper modules.
> > 
> > Personally, I think, I would prefer to have 1 property per flag. Whether
> > we use an integer as above or a boolean as in this patch:
> > 
> > http://thread.gmane.org/gmane.linux.drivers.devicetree/17495
> > 
> > can be discussed.
> 
> I don't have strong preference, but I would vote for
> vsync/hsync/field-active-low; and pclk-sample-falling; boolean keys.
> 
> >>> 			pclk-sample =<1>;	/* rising */
> >>> 			clock-frequency =<24000000>;
> >>> 		
> >>> 		};
> >>> 	
> >>> 	};
> >>> 
> >>> Client devices
> >>> ==============
> >>> 
> >>> Client nodes are children on their respective busses, e.g., i2c. This
> >>> placement leads to these devices being possibly probed before respective
> >>> host interfaces, which will fail due to known reasons. Therefore client
> >>> drivers have to be adapted to request a delayed probing, as long as the
> >>> respective video host hasn't probed.
> >> 
> >> I doubt this is going to be sufficient. Video bridge drivers may require
> >> all their sub-devices (e.g. I2C client devices) to be registered, in
> >> order
> >> to complete their probing. This was discussed in the past:
> >> http://www.mail-archive.com/devicetree-discuss@lists.ozlabs.org/msg06595.
> >> html> 
> > How about this:
> >   - if sensors get probed before the host, they request deferred probing;
> >   - when the host gets probed, it checks, which clients it should be
> >     getting, enables respective clocks, registers a notifier on respective
> >     busses (&i2c_bus_type for I2C) and returns success
> >   
> >   - when after this sensors are re-probed, the notifier gets called and
> >     the host can complete its initialisation
> 
> This could work, the sensor nodes would need to contain a reference to
> their respective media parent nodes. And of course a lot of existing
> code would have to be modified to support that.

I'm not sure I like that. Up to now sensor subdevs can't reference hosts until 
the subdev gets registered. Changing that is of course possible, but I don't 
think it would be worth the effort. 

> I'd like just to point one detail here, as sensor subdev drivers control
> their voltage regulators and RESET/STANDBY (gpio) signals, they should
> also be able to control the master clock. In order to ensure proper power
> up/down sequences. It is a bad practice to enable clocks before voltage
> supplies are switched on and we shouldn't have that as a general
> assumption at the kernel frameworks.
> 
> One possible solution would be to have host/bridge drivers to register
> a clkdev entry for I2C client device, so it can acquire the clock through
> just clk_get(). We would have to ensure the clock is not tried to be
> accessed before it is registered by a bridge. This would require to add
> clock handling code to all sensor/encoder subdev drivers though..

I thik it's a good practice to add clock management to subdevs anyway, and the 
common clock framework should make that easy (or at least not too difficult). 
We can migrate subdevs one by one as we add DT support for them.

> Or maybe we could add some capability flags, so for sensors that don't
> control the clock themselves the hosts would enable/disable it when
> needed.
> 
> >> So we ended up with defining an aggregate DT node that happens to be
> >> associated with the camera media device driver.
> >> 
> >> Here is an example of how it might look like:
> >> https://github.com/snawrocki/linux/commit/eae639132681df6c068dc869bb8973f
> >> 8d9d3efa1 
> > Yeah, it can be done if absolutely needed, but I wouldn't make it
> > mandatory. On simpler sistems 1 host and 1 sensor nodes should suffice.
> > 
> >>> Client nodes will include all the properties, usual for their busses.
> >>> Additionally they will specify properties private to this device type
> >>> and common for all V4L2 client devices - device global and per-link. I
> >>> think,
> >> 
> >> Sounds good.
> >> 
> >>> we should make it possible to define client devices, that can at
> >>> run-time be connected to different sinks, even though such
> >>> configurations might not be very frequent. To achieve this we also
> >>> specify link information in child devices, similar to those in host
> >>> nodes above. This also helps uniformity and will let us implement and
> >>> use a universal link-binding parser. So, a node, that has been
> >>> referenced above could look like
> >> 
> >> It seems dubious to me to push media links' description into DT. Links
> >> can be configurable, and I don't think it's a rare situation. I'm
> >> inclined to code the interconnections within a composite device driver.
> > 
> > Shouldn't a list of all possible links be provided by the platform? If a
> > certain pad can participate in several links, all of them should be
> > specified and at run-time we just switch between them?
> 
> Again, this could be entirely coded in drivers with minimal needed
> information retrieved from DT. Or we could have all possible link
> templates in DT which would then have to be parsed/translated to
> respective user API calls. I'd like to see a real example of such
> link parsing at some driver.

Links internal to the SoC can be created by the driver without help of the DT, 
but links on the board can't. We need the DT to describe how chips are 
physically connected. I don't know if we should aim for something completely 
generic to start with though.

> >>> 	ov772x@0x21-0 = {
> >>> 	
> >>> 		compatible = "omnivision,ov772x";
> >>> 		reg =<0x21>;
> >>> 		vdd-supply =<&regulator>;
> >>> 		bus-width =<10>;
> >>> 		#address-cells =<1>;
> >>> 		#size-cells =<0>;
> >>> 		...
> >>> 		ceu0-1 = {
> >>> 		
> >>> 			reg =<0>;
> >>> 			media-parent =<&ceu0@0xfe910000>;
> >>> 			bus-width =<8>;
> >>> 			hsync-active =<1>;
> >>> 			vsync-active =<0>;	/* who came up with an inverter here?... */
> >>> 			pclk-sample =<1>;
> >>> 		
> >>> 		};
> 
> Don't we need to also specify what sort of video bus (serial/parallel)
> is used in such a client node ? How the sensor sub-device driver would
> determine its bus type ?
> 
> >> Are these mostly supposed to be properties specific to a sub-device and
> >> used by a host ?
> > 
> > These parameters specify the subdevice configuration and are also used by
> > the subdevice to configure its signal polarities.
> > 
> >> If so, how about adding them under the host or the aggregate node grouped
> >> into a sub-device specific child node ?
> > 
> > We need 2 copies of them - for both pads, that's exactly the reason for
> > the above inverter "joke."
> 
> Yeah, I see. But why we need a "ceu0-1" node under "ov772x@0x21-0" node
> above ? A driver associated with ceu0@0xfe910000 node could still access
> properties at "ov772x@0x21-0" node through its "client" phandle.
> I can't see an advantage of having those properties grouped into a media
> parent specific child node under the sensor node. It's not needed by the
> sensor subdev driver, is it ?
> 
> >>> 	};
> >>> 
> >>> Data processors
> >>> ===============
> >>> 
> >>> Data processing modules include resizers, codecs, rotators, serialisers,
> >>> etc. A node for an sh-mobile CSI-2 subdevice could look like
> >>> 
> >>> 	csi2@0xffc90000 = {
> >>> 	
> >>> 		compatible = "renesas,sh-mobile-csi2";
> >>> 		reg =<0xffc90000 0x1000>;
> >>> 		interrupts =<0x17a0>;
> >>> 		bus-width =<4>;
> >>> 		clock-frequency =<30000000>;
> >>> 		...
> >>> 		imx074-1 = {
> >>> 		
> >>> 			client =<&imx074@0x1a-0>;
> >>> 			local-pad = "csi2-sink";
> >>> 			remote-pad = "csi2-source";
> >>> 			bus-width =<2>;
> >>> 			clock-frequency =<25000000>;
> >>> 			csi2-crc;
> >>> 			csi2-ecc;
> >>> 			sh-csi2,phy =<0>;
> >>> 		
> >>> 		};
> >>> 		ceu0 = {
> >>> 		
> >>> 			media-parent =<&ceu0@0xfe910000>;
> >>> 			immutable;
> >>> 		
> >>> 		};
> 
> The child nodes don't seem to have standard names. How would the csi2
> driver determine what is the purpose of each of them ?
> 
> >>> 	};
> >>> 
> >>> The respective child binding in the CEU node could then look like
> >>> 
> >>> 		csi2-1 = {
> >>> 		
> >>> 			reg =<1>;
> >>> 			client =<&csi2@0xffc90000>;
> >>> 			immutable;
> >>> 		
> >>> 		};
> >> 
> >> It look a bit complex, and could more complex when we run into a system
> >> supporting more complex interconnections. I would prefer some sort of
> >> more flat structure...
> > 
> > Ideas welcome:-)
>
> :) It just looked to me like a lot of parsing code for all these constructs.
> 
> And would such design be flexible enough to support pipelines like:
> 
> [sensor] -> [MIPI-CSI2 receiver (frontend)] -> [ISP frontend (+ DMA)] ->
> [ISP (...)] -> [scaler/rotator + DMA] ->
> 
> i.e. containing more than 3 entities ?

-- 
Regards,

Laurent Pinchart

Re: [RFC] media DT bindings

[Guennadi Liakhovetski]

On Fri, 27 Jul 2012, Laurent Pinchart wrote:

> Hi Sylwester,
> 
> On Wednesday 18 July 2012 19:00:15 Sylwester Nawrocki wrote:
> > On 07/16/2012 01:41 PM, Guennadi Liakhovetski wrote:

[snip]

> > >>> An sh-mobile CEU DT node could look like
> > >>> 
> > >>> 	ceu0@0xfe910000 = {
> > >>> 	
> > >>> 		compatible = "renesas,sh-mobile-ceu";
> > >>> 		reg =<0xfe910000 0xa0>;
> > >>> 		interrupts =<0x880>;
> > >>> 		bus-width =<16>;		/* #lines routed on the board */
> > >>> 		clock-frequency =<50000000>;	/* max clock */
> > >>> 		#address-cells =<1>;
> > >>> 		#size-cells =<0>;
> > >>> 		...
> > >>> 		ov772x-1 = {
> > >>> 		
> > >>> 			reg =<0>;
> > 
> > This property might be redundant, we already have the "client" phandle
> > pointing to "ov772x@0x21-0", which has all interesting properties inside
> > it. Other than there is probably no reasonable usage for it under
> > "ceu0@0xfe910000" node ?
> > 
> > >>> 			client =<&ov772x@0x21-0>;
> > >>> 			local-pad = "parallel-sink";
> > >>> 			remote-pad = "parallel-source";
> > >> 
> > >> I'm not sure I like that. Is it really needed when we already have
> > >> the child/parent properties around ?
> > > 
> > > I think it is. Both the host and the client can have multiple pads (e.g.,
> > > parallel / serial). These properties specify which pads are used and make
> > > the translation between DT data and our subdev / pad APIs simpler.
> > 
> > OK, sorry, but isn't it all about just specifying what sort of data bus
> > is used ? :-)
> 
> In some (many/most ?) cases probably, but not in all of them.
> 
> What about merging the client and remote-pad properties ? The resulting 
> property would then reference a pad with <&ov772x@0x21-0 0>.

What would the "0" parameter mean then? Pad #0? But aren't these numbers 
device specific? Maybe not a huge deal, but these numbers are defind by 
the driver, right? Not the DT itself. So, drivers then will have to take 
care not to change their pad numbering. Whereas using strings, we can fix 
strings in the common V4L DT spec and keep them standard across devices 
and drivers. Then drivers might be less likely to change these assignments 
randomly;-)

[snip]

> > I'd like just to point one detail here, as sensor subdev drivers control
> > their voltage regulators and RESET/STANDBY (gpio) signals, they should
> > also be able to control the master clock. In order to ensure proper power
> > up/down sequences. It is a bad practice to enable clocks before voltage
> > supplies are switched on and we shouldn't have that as a general
> > assumption at the kernel frameworks.
> > 
> > One possible solution would be to have host/bridge drivers to register
> > a clkdev entry for I2C client device, so it can acquire the clock through
> > just clk_get(). We would have to ensure the clock is not tried to be
> > accessed before it is registered by a bridge. This would require to add
> > clock handling code to all sensor/encoder subdev drivers though..
> 
> I thik it's a good practice to add clock management to subdevs anyway, and the 
> common clock framework should make that easy (or at least not too difficult). 
> We can migrate subdevs one by one as we add DT support for them.

Yes, this would be good.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/

Re: [RFC] media DT bindings

[Laurent Pinchart]

Hi Guennadi,

On Tuesday 31 July 2012 11:26:27 Guennadi Liakhovetski wrote:
> On Fri, 27 Jul 2012, Laurent Pinchart wrote:
> > Hi Sylwester,
> > 
> > On Wednesday 18 July 2012 19:00:15 Sylwester Nawrocki wrote:
> > > On 07/16/2012 01:41 PM, Guennadi Liakhovetski wrote:
> [snip]
> 
> > > >>> An sh-mobile CEU DT node could look like
> > > >>> 
> > > >>> 	ceu0@0xfe910000 = {
> > > >>> 	
> > > >>> 		compatible = "renesas,sh-mobile-ceu";
> > > >>> 		reg =<0xfe910000 0xa0>;
> > > >>> 		interrupts =<0x880>;
> > > >>> 		bus-width =<16>;		/* #lines routed on the board */
> > > >>> 		clock-frequency =<50000000>;	/* max clock */
> > > >>> 		#address-cells =<1>;
> > > >>> 		#size-cells =<0>;
> > > >>> 		...
> > > >>> 		ov772x-1 = {
> > > >>> 		
> > > >>> 			reg =<0>;
> > > 
> > > This property might be redundant, we already have the "client" phandle
> > > pointing to "ov772x@0x21-0", which has all interesting properties inside
> > > it. Other than there is probably no reasonable usage for it under
> > > "ceu0@0xfe910000" node ?
> > > 
> > > >>> 			client =<&ov772x@0x21-0>;
> > > >>> 			local-pad = "parallel-sink";
> > > >>> 			remote-pad = "parallel-source";
> > > >> 
> > > >> I'm not sure I like that. Is it really needed when we already have
> > > >> the child/parent properties around ?
> > > > 
> > > > I think it is. Both the host and the client can have multiple pads
> > > > (e.g.,
> > > > parallel / serial). These properties specify which pads are used and
> > > > make
> > > > the translation between DT data and our subdev / pad APIs simpler.
> > > 
> > > OK, sorry, but isn't it all about just specifying what sort of data bus
> > > is used ? :-)
> > 
> > In some (many/most ?) cases probably, but not in all of them.
> > 
> > What about merging the client and remote-pad properties ? The resulting
> > property would then reference a pad with <&ov772x@0x21-0 0>.
> 
> What would the "0" parameter mean then? Pad #0?

Yes.

> But aren't these numbers device specific? Maybe not a huge deal, but these
> numbers are defind by the driver, right? Not the DT itself. So, drivers then
> will have to take care not to change their pad numbering. Whereas using
> strings, we can fix strings in the common V4L DT spec and keep them standard
> across devices and drivers. Then drivers might be less likely to change
> these assignments randomly ;-)

Userspace applications usually rely on pad numbers as well, so I consider them 
as more or less part of the ABI. If we really need to, we could add a DT pad 
number -> media controller pad number conversion in the driver, that would be 
less expensive than pad name -> pad number conversion (especially since it 
would be skipped in most cases).

> [snip]
> 
> > > I'd like just to point one detail here, as sensor subdev drivers control
> > > their voltage regulators and RESET/STANDBY (gpio) signals, they should
> > > also be able to control the master clock. In order to ensure proper
> > > power
> > > up/down sequences. It is a bad practice to enable clocks before voltage
> > > supplies are switched on and we shouldn't have that as a general
> > > assumption at the kernel frameworks.
> > > 
> > > One possible solution would be to have host/bridge drivers to register
> > > a clkdev entry for I2C client device, so it can acquire the clock
> > > through
> > > just clk_get(). We would have to ensure the clock is not tried to be
> > > accessed before it is registered by a bridge. This would require to add
> > > clock handling code to all sensor/encoder subdev drivers though..
> > 
> > I thik it's a good practice to add clock management to subdevs anyway, and
> > the common clock framework should make that easy (or at least not too
> > difficult). We can migrate subdevs one by one as we add DT support for
> > them.
> 
> Yes, this would be good.

-- 
Regards,

Laurent Pinchart

Re: [RFC] media DT bindings

[Guennadi Liakhovetski]

On Tue, 31 Jul 2012, Laurent Pinchart wrote:

> Hi Guennadi,
> 
> On Tuesday 31 July 2012 11:26:27 Guennadi Liakhovetski wrote:
> > On Fri, 27 Jul 2012, Laurent Pinchart wrote:
> > > Hi Sylwester,
> > > 
> > > On Wednesday 18 July 2012 19:00:15 Sylwester Nawrocki wrote:
> > > > On 07/16/2012 01:41 PM, Guennadi Liakhovetski wrote:
> > [snip]
> > 
> > > > >>> An sh-mobile CEU DT node could look like
> > > > >>> 
> > > > >>> 	ceu0@0xfe910000 = {
> > > > >>> 	
> > > > >>> 		compatible = "renesas,sh-mobile-ceu";
> > > > >>> 		reg =<0xfe910000 0xa0>;
> > > > >>> 		interrupts =<0x880>;
> > > > >>> 		bus-width =<16>;		/* #lines routed on the board */
> > > > >>> 		clock-frequency =<50000000>;	/* max clock */
> > > > >>> 		#address-cells =<1>;
> > > > >>> 		#size-cells =<0>;
> > > > >>> 		...
> > > > >>> 		ov772x-1 = {
> > > > >>> 		
> > > > >>> 			reg =<0>;
> > > > 
> > > > This property might be redundant, we already have the "client" phandle
> > > > pointing to "ov772x@0x21-0", which has all interesting properties inside
> > > > it. Other than there is probably no reasonable usage for it under
> > > > "ceu0@0xfe910000" node ?
> > > > 
> > > > >>> 			client =<&ov772x@0x21-0>;
> > > > >>> 			local-pad = "parallel-sink";
> > > > >>> 			remote-pad = "parallel-source";
> > > > >> 
> > > > >> I'm not sure I like that. Is it really needed when we already have
> > > > >> the child/parent properties around ?
> > > > > 
> > > > > I think it is. Both the host and the client can have multiple pads
> > > > > (e.g.,
> > > > > parallel / serial). These properties specify which pads are used and
> > > > > make
> > > > > the translation between DT data and our subdev / pad APIs simpler.
> > > > 
> > > > OK, sorry, but isn't it all about just specifying what sort of data bus
> > > > is used ? :-)
> > > 
> > > In some (many/most ?) cases probably, but not in all of them.
> > > 
> > > What about merging the client and remote-pad properties ? The resulting
> > > property would then reference a pad with <&ov772x@0x21-0 0>.
> > 
> > What would the "0" parameter mean then? Pad #0?
> 
> Yes.
> 
> > But aren't these numbers device specific? Maybe not a huge deal, but these
> > numbers are defind by the driver, right? Not the DT itself. So, drivers then
> > will have to take care not to change their pad numbering. Whereas using
> > strings, we can fix strings in the common V4L DT spec and keep them standard
> > across devices and drivers. Then drivers might be less likely to change
> > these assignments randomly ;-)
> 
> Userspace applications usually rely on pad numbers as well, so I consider them 
> as more or less part of the ABI. If we really need to, we could add a DT pad 
> number -> media controller pad number conversion in the driver, that would be 
> less expensive than pad name -> pad number conversion (especially since it 
> would be skipped in most cases).

Ok, then, how about

		#address-cells = <1>;
		#size-cells = <0>;
		...
		ov772x-1 = {
			reg = <1>;			/* local pad # */
			client = <&ov772x@0x21-0 0>;	/* remote phandle and pad */


Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/

Re: [RFC] media DT bindings

[Laurent Pinchart]

Hi Guennadi,

On Tuesday 31 July 2012 14:39:07 Guennadi Liakhovetski wrote:
> On Tue, 31 Jul 2012, Laurent Pinchart wrote:
> > On Tuesday 31 July 2012 11:26:27 Guennadi Liakhovetski wrote:
> > > On Fri, 27 Jul 2012, Laurent Pinchart wrote:
> > > > On Wednesday 18 July 2012 19:00:15 Sylwester Nawrocki wrote:
> > > > > On 07/16/2012 01:41 PM, Guennadi Liakhovetski wrote:
> > > [snip]
> > > 
> > > > > >>> An sh-mobile CEU DT node could look like
> > > > > >>> 
> > > > > >>> 	ceu0@0xfe910000 = {
> > > > > >>> 	
> > > > > >>> 		compatible = "renesas,sh-mobile-ceu";
> > > > > >>> 		reg =<0xfe910000 0xa0>;
> > > > > >>> 		interrupts =<0x880>;
> > > > > >>> 		bus-width =<16>;		/* #lines routed on the board */
> > > > > >>> 		clock-frequency =<50000000>;	/* max clock */
> > > > > >>> 		#address-cells =<1>;
> > > > > >>> 		#size-cells =<0>;
> > > > > >>> 		...
> > > > > >>> 		ov772x-1 = {
> > > > > >>> 		
> > > > > >>> 			reg =<0>;
> > > > > 
> > > > > This property might be redundant, we already have the "client"
> > > > > phandle pointing to "ov772x@0x21-0", which has all interesting
> > > > > properties inside it. Other than there is probably no reasonable
> > > > > usage for it under "ceu0@0xfe910000" node ?
> > > > > 
> > > > > >>> 			client =<&ov772x@0x21-0>;
> > > > > >>> 			local-pad = "parallel-sink";
> > > > > >>> 			remote-pad = "parallel-source";
> > > > > >> 
> > > > > >> I'm not sure I like that. Is it really needed when we already
> > > > > >> have the child/parent properties around ?
> > > > > > 
> > > > > > I think it is. Both the host and the client can have multiple pads
> > > > > > (e.g., parallel / serial). These properties specify which pads are
> > > > > > used and make the translation between DT data and our subdev / pad
> > > > > > APIs simpler.
> > > > > 
> > > > > OK, sorry, but isn't it all about just specifying what sort of data
> > > > > bus is used ? :-)
> > > > 
> > > > In some (many/most ?) cases probably, but not in all of them.
> > > > 
> > > > What about merging the client and remote-pad properties ? The
> > > > resulting property would then reference a pad with <&ov772x@0x21-0 0>.
> > > 
> > > What would the "0" parameter mean then? Pad #0?
> > 
> > Yes.
> > 
> > > But aren't these numbers device specific? Maybe not a huge deal, but
> > > these numbers are defind by the driver, right? Not the DT itself. So,
> > > drivers then will have to take care not to change their pad numbering.
> > > Whereas using strings, we can fix strings in the common V4L DT spec and
> > > keep them standard across devices and drivers. Then drivers might be
> > > less likely to change these assignments randomly ;-)
> > 
> > Userspace applications usually rely on pad numbers as well, so I consider
> > them as more or less part of the ABI. If we really need to, we could add
> > a DT pad number -> media controller pad number conversion in the driver,
> > that would be less expensive than pad name -> pad number conversion
> > (especially since it would be skipped in most cases).
> 
> Ok, then, how about
> 
> 		#address-cells = <1>;
> 		#size-cells = <0>;
> 		...
> 		ov772x-1 = {
> 			reg = <1>;			/* local pad # */
> 			client = <&ov772x@0x21-0 0>;	/* remote phandle and pad */

The client property looks good, but isn't such a usage of the reg property an 
abuse ? Maybe the local pad # should be a device-specific property. Many hosts 
won't need it, and on others it would actually need to reference a subdev, not 
just a pad.

-- 
Regards,

Laurent Pinchart

Re: [RFC] media DT bindings

[Stephen Warren]

On 07/31/2012 03:22 PM, Laurent Pinchart wrote:
> On Tuesday 31 July 2012 14:39:07 Guennadi Liakhovetski wrote:
...
>> Ok, then, how about
>>
>> 		#address-cells = <1>;
>> 		#size-cells = <0>;
>> 		...
>> 		ov772x-1 = {
>> 			reg = <1>;			/* local pad # */
>> 			client = <&ov772x@0x21-0 0>;	/* remote phandle and pad */
> 
> The client property looks good, but isn't such a usage of the reg property an 
> abuse ? Maybe the local pad # should be a device-specific property. Many hosts 
> won't need it, and on others it would actually need to reference a subdev, not 
> just a pad.

That's a very odd syntax the the phandle; I assume that "&ov772x@0x21-0"
is supposed to reference some other DT node. However, other nodes are
either referenced by:

"&foo" where foo is a label, and the label name is unlikely to include
the text "@0x21"; the @ symbol probably isn't even legal in label names.

"&{/path/to/node}" which might include the "@0x21" syntax since it might
be part of the node's name, but your example didn't include {}.

I'm not sure what "-0" is meant to be in that string - a math
expression, or ...? If it's intended to represent some separate field
relative to the node the phandle references, it needs to be just another
cell.

So overall, perhaps:

/ {
   ...
   pad: something { ... };
   ...
   ov772x@1 = { /* @1 not -1 would be canonical syntax */
     reg = <1>;
     client = <&pad 0 0>;
   ...

I'm sorry I haven't followed the thread; I'm wondering why a client is a
pad, which to me means a pin/pad/ball on an IC package, so I'm still not
entirely sure if even this makes sense.

Re: [RFC] media DT bindings

[Laurent Pinchart]

Hi Stephen,

On Tuesday 31 July 2012 17:29:24 Stephen Warren wrote:
> On 07/31/2012 03:22 PM, Laurent Pinchart wrote:
> > On Tuesday 31 July 2012 14:39:07 Guennadi Liakhovetski wrote:
> ...
> 
> >> Ok, then, how about
> >> 
> >> 		#address-cells = <1>;
> >> 		#size-cells = <0>;
> >> 		...
> >> 		ov772x-1 = {
> >> 		
> >> 			reg = <1>;			/* local pad # */
> >> 			client = <&ov772x@0x21-0 0>;	/* remote phandle and pad */
> > 
> > The client property looks good, but isn't such a usage of the reg property
> > an abuse ? Maybe the local pad # should be a device-specific property.
> > Many hosts won't need it, and on others it would actually need to
> > reference a subdev, not just a pad.
> 
> That's a very odd syntax the the phandle; I assume that "&ov772x@0x21-0"
> is supposed to reference some other DT node. However, other nodes are
> either referenced by:
> 
> "&foo" where foo is a label, and the label name is unlikely to include
> the text "@0x21"; the @ symbol probably isn't even legal in label names.
> 
> "&{/path/to/node}" which might include the "@0x21" syntax since it might
> be part of the node's name, but your example didn't include {}.
> 
> I'm not sure what "-0" is meant to be in that string - a math
> expression, or ...? If it's intended to represent some separate field
> relative to the node the phandle references, it needs to be just another
> cell.

I'm actually not sure what -0 represents, and I don't think we need the 
@0x21-0 at all. I believe &ov772x@0x21-0 is supposed to just be a label. We 
don't need an extra cell.

> So overall, perhaps:
> 
> / {
>    ...
>    pad: something { ... };
>    ...
>    ov772x@1 = { /* @1 not -1 would be canonical syntax */
>      reg = <1>;
>      client = <&pad 0 0>;
>    ...
> 
> I'm sorry I haven't followed the thread; I'm wondering why a client is a
> pad, which to me means a pin/pad/ball on an IC package, so I'm still not
> entirely sure if even this makes sense.

Client references an image source (which is usually an I2C client, but can be 
a different type of device) and a pad. Pad refers here to a media entity pad 
(see http://linuxtv.org/downloads/v4l-dvb-apis/media-controller-model.html), 
not a physical pin on an IC package.

-- 
Regards,

Laurent Pinchart

Re: [RFC] media DT bindings

[Stephen Warren]

On 07/31/2012 11:59 PM, Laurent Pinchart wrote:
> Hi Stephen,
> 
> On Tuesday 31 July 2012 17:29:24 Stephen Warren wrote:
>> On 07/31/2012 03:22 PM, Laurent Pinchart wrote:
>>> On Tuesday 31 July 2012 14:39:07 Guennadi Liakhovetski wrote:
>> ...
>>
>>>> Ok, then, how about
>>>>
>>>> 		#address-cells = <1>;
>>>> 		#size-cells = <0>;
>>>> 		...
>>>> 		ov772x-1 = {
>>>> 		
>>>> 			reg = <1>;			/* local pad # */
>>>> 			client = <&ov772x@0x21-0 0>;	/* remote phandle and pad */
>>>
>>> The client property looks good, but isn't such a usage of the reg property
>>> an abuse ? Maybe the local pad # should be a device-specific property.
>>> Many hosts won't need it, and on others it would actually need to
>>> reference a subdev, not just a pad.
>>
>> That's a very odd syntax the the phandle; I assume that "&ov772x@0x21-0"
>> is supposed to reference some other DT node. However, other nodes are
>> either referenced by:
>>
>> "&foo" where foo is a label, and the label name is unlikely to include
>> the text "@0x21"; the @ symbol probably isn't even legal in label names.
>>
>> "&{/path/to/node}" which might include the "@0x21" syntax since it might
>> be part of the node's name, but your example didn't include {}.
>>
>> I'm not sure what "-0" is meant to be in that string - a math
>> expression, or ...? If it's intended to represent some separate field
>> relative to the node the phandle references, it needs to be just another
>> cell.
> 
> I'm actually not sure what -0 represents, and I don't think we need the 
> @0x21-0 at all. I believe &ov772x@0x21-0 is supposed to just be a label. We 
> don't need an extra cell.

Ah, OK. The lexer in dtc has the following definition for label names:

LABEL		[a-zA-Z_][a-zA-Z0-9_]*

Re: [RFC] media DT bindings

[Guennadi Liakhovetski]

On Tue, 31 Jul 2012, Laurent Pinchart wrote:

> Hi Guennadi,
> 
> On Tuesday 31 July 2012 14:39:07 Guennadi Liakhovetski wrote:
> > On Tue, 31 Jul 2012, Laurent Pinchart wrote:
> > > On Tuesday 31 July 2012 11:26:27 Guennadi Liakhovetski wrote:
> > > > On Fri, 27 Jul 2012, Laurent Pinchart wrote:
> > > > > On Wednesday 18 July 2012 19:00:15 Sylwester Nawrocki wrote:
> > > > > > On 07/16/2012 01:41 PM, Guennadi Liakhovetski wrote:
> > > > [snip]
> > > > 
> > > > > > >>> An sh-mobile CEU DT node could look like
> > > > > > >>> 
> > > > > > >>> 	ceu0@0xfe910000 = {
> > > > > > >>> 	
> > > > > > >>> 		compatible = "renesas,sh-mobile-ceu";
> > > > > > >>> 		reg =<0xfe910000 0xa0>;
> > > > > > >>> 		interrupts =<0x880>;
> > > > > > >>> 		bus-width =<16>;		/* #lines routed on the board */
> > > > > > >>> 		clock-frequency =<50000000>;	/* max clock */
> > > > > > >>> 		#address-cells =<1>;
> > > > > > >>> 		#size-cells =<0>;
> > > > > > >>> 		...
> > > > > > >>> 		ov772x-1 = {
> > > > > > >>> 		
> > > > > > >>> 			reg =<0>;
> > > > > > 
> > > > > > This property might be redundant, we already have the "client"
> > > > > > phandle pointing to "ov772x@0x21-0", which has all interesting
> > > > > > properties inside it. Other than there is probably no reasonable
> > > > > > usage for it under "ceu0@0xfe910000" node ?
> > > > > > 
> > > > > > >>> 			client =<&ov772x@0x21-0>;
> > > > > > >>> 			local-pad = "parallel-sink";
> > > > > > >>> 			remote-pad = "parallel-source";
> > > > > > >> 
> > > > > > >> I'm not sure I like that. Is it really needed when we already
> > > > > > >> have the child/parent properties around ?
> > > > > > > 
> > > > > > > I think it is. Both the host and the client can have multiple pads
> > > > > > > (e.g., parallel / serial). These properties specify which pads are
> > > > > > > used and make the translation between DT data and our subdev / pad
> > > > > > > APIs simpler.
> > > > > > 
> > > > > > OK, sorry, but isn't it all about just specifying what sort of data
> > > > > > bus is used ? :-)
> > > > > 
> > > > > In some (many/most ?) cases probably, but not in all of them.
> > > > > 
> > > > > What about merging the client and remote-pad properties ? The
> > > > > resulting property would then reference a pad with <&ov772x@0x21-0 0>.
> > > > 
> > > > What would the "0" parameter mean then? Pad #0?
> > > 
> > > Yes.
> > > 
> > > > But aren't these numbers device specific? Maybe not a huge deal, but
> > > > these numbers are defind by the driver, right? Not the DT itself. So,
> > > > drivers then will have to take care not to change their pad numbering.
> > > > Whereas using strings, we can fix strings in the common V4L DT spec and
> > > > keep them standard across devices and drivers. Then drivers might be
> > > > less likely to change these assignments randomly ;-)
> > > 
> > > Userspace applications usually rely on pad numbers as well, so I consider
> > > them as more or less part of the ABI. If we really need to, we could add
> > > a DT pad number -> media controller pad number conversion in the driver,
> > > that would be less expensive than pad name -> pad number conversion
> > > (especially since it would be skipped in most cases).
> > 
> > Ok, then, how about
> > 
> > 		#address-cells = <1>;
> > 		#size-cells = <0>;
> > 		...
> > 		ov772x-1 = {
> > 			reg = <1>;			/* local pad # */
> > 			client = <&ov772x@0x21-0 0>;	/* remote phandle and pad */
> 
> The client property looks good, but isn't such a usage of the reg property an 
> abuse ?

Don't know, is it?

> Maybe the local pad # should be a device-specific property. Many hosts 
> won't need it, and on others it would actually need to reference a subdev, not 
> just a pad.

Wait, the correspondence cannot be one pad to many subdevs, right? So, we 
always can assign at least 1 pad to each subdev. Hm, or you mean subdevs 
like flash, that don't access data, in which case they don't need pads? 
but then we also don't need links to them. Those child nodes are links, 
and links always run between 2 pads, right? So, in the above 
representation child devices are pads of the parent node, to which other 
entities are linked.

But while writing this, another question occurred to me: what if several 
entities are connected to one pad (activated selectively by a switch)? We 
cannot have several child nodes with the same address. But in such a case 
we could use

	#address-cells = <2>;
	...
	subdev1 = {
		reg = <1 1>; /* first client on pad 1 */
	};

	subdev2 = {
		reg = <1 2>; /* second client on pad 1 */
	};

But I'm not particularly attached to this idea. If we decide, that it's an 
abuse, we can switch back to some property.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/

Re: [RFC] media DT bindings

[Laurent Pinchart]

Hi Guennadi,

On Wednesday 01 August 2012 08:47:20 Guennadi Liakhovetski wrote:
> On Tue, 31 Jul 2012, Laurent Pinchart wrote:
> > On Tuesday 31 July 2012 14:39:07 Guennadi Liakhovetski wrote:
> > > On Tue, 31 Jul 2012, Laurent Pinchart wrote:
> > > > On Tuesday 31 July 2012 11:26:27 Guennadi Liakhovetski wrote:
> > > > > On Fri, 27 Jul 2012, Laurent Pinchart wrote:
> > > > > > On Wednesday 18 July 2012 19:00:15 Sylwester Nawrocki wrote:
> > > > > > > On 07/16/2012 01:41 PM, Guennadi Liakhovetski wrote:
> > > > > [snip]
> > > > > 
> > > > > > > >>> An sh-mobile CEU DT node could look like
> > > > > > > >>> 
> > > > > > > >>> 	ceu0@0xfe910000 = {
> > > > > > > >>> 	
> > > > > > > >>> 		compatible = "renesas,sh-mobile-ceu";
> > > > > > > >>> 		reg =<0xfe910000 0xa0>;
> > > > > > > >>> 		interrupts =<0x880>;
> > > > > > > >>> 		bus-width =<16>;		/* #lines routed on the board */
> > > > > > > >>> 		clock-frequency =<50000000>;	/* max clock */
> > > > > > > >>> 		#address-cells =<1>;
> > > > > > > >>> 		#size-cells =<0>;
> > > > > > > >>> 		...
> > > > > > > >>> 		ov772x-1 = {
> > > > > > > >>> 		
> > > > > > > >>> 			reg =<0>;
> > > > > > > 
> > > > > > > This property might be redundant, we already have the "client"
> > > > > > > phandle pointing to "ov772x@0x21-0", which has all interesting
> > > > > > > properties inside it. Other than there is probably no reasonable
> > > > > > > usage for it under "ceu0@0xfe910000" node ?
> > > > > > > 
> > > > > > > >>> 			client =<&ov772x@0x21-0>;
> > > > > > > >>> 			local-pad = "parallel-sink";
> > > > > > > >>> 			remote-pad = "parallel-source";
> > > > > > > >> 
> > > > > > > >> I'm not sure I like that. Is it really needed when we already
> > > > > > > >> have the child/parent properties around ?
> > > > > > > > 
> > > > > > > > I think it is. Both the host and the client can have multiple
> > > > > > > > pads (e.g., parallel / serial). These properties specify which
> > > > > > > > pads are used and make the translation between DT data and our
> > > > > > > > subdev / pad APIs simpler.
> > > > > > > 
> > > > > > > OK, sorry, but isn't it all about just specifying what sort of
> > > > > > > data bus is used ? :-)
> > > > > > 
> > > > > > In some (many/most ?) cases probably, but not in all of them.
> > > > > > 
> > > > > > What about merging the client and remote-pad properties ? The
> > > > > > resulting property would then reference a pad with <&ov772x@0x21-0
> > > > > > 0>.
> > > > > 
> > > > > What would the "0" parameter mean then? Pad #0?
> > > > 
> > > > Yes.
> > > > 
> > > > > But aren't these numbers device specific? Maybe not a huge deal, but
> > > > > these numbers are defind by the driver, right? Not the DT itself.
> > > > > So, drivers then will have to take care not to change their pad
> > > > > numbering. Whereas using strings, we can fix strings in the common
> > > > > V4L DT spec and keep them standard across devices and drivers. Then
> > > > > drivers might be less likely to change these assignments randomly
> > > > > ;-)
> > > > 
> > > > Userspace applications usually rely on pad numbers as well, so I
> > > > consider them as more or less part of the ABI. If we really need to,
> > > > we could add a DT pad number -> media controller pad number conversion
> > > > in the driver, that would be less expensive than pad name -> pad
> > > > number conversion (especially since it would be skipped in most
> > > > cases).
> > > 
> > > Ok, then, how about
> > > 
> > > 		#address-cells = <1>;
> > > 		#size-cells = <0>;
> > > 		...
> > > 		ov772x-1 = {
> > > 		
> > > 			reg = <1>;			/* local pad # */
> > > 			client = <&ov772x@0x21-0 0>;	/* remote phandle and pad */
> > 
> > The client property looks good, but isn't such a usage of the reg property
> > an abuse ?
> 
> Don't know, is it?
> 
> > Maybe the local pad # should be a device-specific property. Many hosts
> > won't need it, and on others it would actually need to reference a subdev,
> > not just a pad.
> 
> Wait, the correspondence cannot be one pad to many subdevs, right?
> So, we always can assign at least 1 pad to each subdev. Hm, or you mean
> subdevs like flash, that don't access data, in which case they don't need
> pads? but then we also don't need links to them. Those child nodes are
> links, and links always run between 2 pads, right? So, in the above
> representation child devices are pads of the parent node, to which other
> entities are linked.
> 
> But while writing this, another question occurred to me: what if several
> entities are connected to one pad (activated selectively by a switch)? We
> cannot have several child nodes with the same address. But in such a case
> we could use
> 
> 	#address-cells = <2>;
> 	...
> 	subdev1 = {
> 		reg = <1 1>; /* first client on pad 1 */
> 	};
> 
> 	subdev2 = {
> 		reg = <1 2>; /* second client on pad 1 */
> 	};
> 
> But I'm not particularly attached to this idea. If we decide, that it's an
> abuse, we can switch back to some property.

I think that would be an abuse :-)

My point was that a host represented by a single DT node might contain several 
media entities. For instance the OMAP3 ISP contains two CSI2 receivers. Each 
of them has a single sink pad, both numbered 0. The DT link representation 
thus needs to mention which sink entity the sensor is connected to, in 
addition to the pad number in that entity (and in the OMAP3 ISP case the pad 
number could be omitted completely, as the CSI2 receivers have a single sink 
pad).

-- 
Regards,

Laurent Pinchart

Re: [RFC] media DT bindings

[Guennadi Liakhovetski]

On Wed, 1 Aug 2012, Laurent Pinchart wrote:

> Hi Guennadi,
> 
> On Wednesday 01 August 2012 08:47:20 Guennadi Liakhovetski wrote:
> > On Tue, 31 Jul 2012, Laurent Pinchart wrote:
> > > On Tuesday 31 July 2012 14:39:07 Guennadi Liakhovetski wrote:
> > > > On Tue, 31 Jul 2012, Laurent Pinchart wrote:
> > > > > On Tuesday 31 July 2012 11:26:27 Guennadi Liakhovetski wrote:
> > > > > > On Fri, 27 Jul 2012, Laurent Pinchart wrote:
> > > > > > > On Wednesday 18 July 2012 19:00:15 Sylwester Nawrocki wrote:
> > > > > > > > On 07/16/2012 01:41 PM, Guennadi Liakhovetski wrote:
> > > > > > [snip]
> > > > > > 
> > > > > > > > >>> An sh-mobile CEU DT node could look like
> > > > > > > > >>> 
> > > > > > > > >>> 	ceu0@0xfe910000 = {
> > > > > > > > >>> 	
> > > > > > > > >>> 		compatible = "renesas,sh-mobile-ceu";
> > > > > > > > >>> 		reg =<0xfe910000 0xa0>;
> > > > > > > > >>> 		interrupts =<0x880>;
> > > > > > > > >>> 		bus-width =<16>;		/* #lines routed on the board */
> > > > > > > > >>> 		clock-frequency =<50000000>;	/* max clock */
> > > > > > > > >>> 		#address-cells =<1>;
> > > > > > > > >>> 		#size-cells =<0>;
> > > > > > > > >>> 		...
> > > > > > > > >>> 		ov772x-1 = {
> > > > > > > > >>> 		
> > > > > > > > >>> 			reg =<0>;
> > > > > > > > 
> > > > > > > > This property might be redundant, we already have the "client"
> > > > > > > > phandle pointing to "ov772x@0x21-0", which has all interesting
> > > > > > > > properties inside it. Other than there is probably no reasonable
> > > > > > > > usage for it under "ceu0@0xfe910000" node ?
> > > > > > > > 
> > > > > > > > >>> 			client =<&ov772x@0x21-0>;
> > > > > > > > >>> 			local-pad = "parallel-sink";
> > > > > > > > >>> 			remote-pad = "parallel-source";
> > > > > > > > >> 
> > > > > > > > >> I'm not sure I like that. Is it really needed when we already
> > > > > > > > >> have the child/parent properties around ?
> > > > > > > > > 
> > > > > > > > > I think it is. Both the host and the client can have multiple
> > > > > > > > > pads (e.g., parallel / serial). These properties specify which
> > > > > > > > > pads are used and make the translation between DT data and our
> > > > > > > > > subdev / pad APIs simpler.
> > > > > > > > 
> > > > > > > > OK, sorry, but isn't it all about just specifying what sort of
> > > > > > > > data bus is used ? :-)
> > > > > > > 
> > > > > > > In some (many/most ?) cases probably, but not in all of them.
> > > > > > > 
> > > > > > > What about merging the client and remote-pad properties ? The
> > > > > > > resulting property would then reference a pad with <&ov772x@0x21-0
> > > > > > > 0>.
> > > > > > 
> > > > > > What would the "0" parameter mean then? Pad #0?
> > > > > 
> > > > > Yes.
> > > > > 
> > > > > > But aren't these numbers device specific? Maybe not a huge deal, but
> > > > > > these numbers are defind by the driver, right? Not the DT itself.
> > > > > > So, drivers then will have to take care not to change their pad
> > > > > > numbering. Whereas using strings, we can fix strings in the common
> > > > > > V4L DT spec and keep them standard across devices and drivers. Then
> > > > > > drivers might be less likely to change these assignments randomly
> > > > > > ;-)
> > > > > 
> > > > > Userspace applications usually rely on pad numbers as well, so I
> > > > > consider them as more or less part of the ABI. If we really need to,
> > > > > we could add a DT pad number -> media controller pad number conversion
> > > > > in the driver, that would be less expensive than pad name -> pad
> > > > > number conversion (especially since it would be skipped in most
> > > > > cases).
> > > > 
> > > > Ok, then, how about
> > > > 
> > > > 		#address-cells = <1>;
> > > > 		#size-cells = <0>;
> > > > 		...
> > > > 		ov772x-1 = {
> > > > 		
> > > > 			reg = <1>;			/* local pad # */
> > > > 			client = <&ov772x@0x21-0 0>;	/* remote phandle and pad */
> > > 
> > > The client property looks good, but isn't such a usage of the reg property
> > > an abuse ?
> > 
> > Don't know, is it?
> > 
> > > Maybe the local pad # should be a device-specific property. Many hosts
> > > won't need it, and on others it would actually need to reference a subdev,
> > > not just a pad.
> > 
> > Wait, the correspondence cannot be one pad to many subdevs, right?
> > So, we always can assign at least 1 pad to each subdev. Hm, or you mean
> > subdevs like flash, that don't access data, in which case they don't need
> > pads? but then we also don't need links to them. Those child nodes are
> > links, and links always run between 2 pads, right? So, in the above
> > representation child devices are pads of the parent node, to which other
> > entities are linked.
> > 
> > But while writing this, another question occurred to me: what if several
> > entities are connected to one pad (activated selectively by a switch)? We
> > cannot have several child nodes with the same address. But in such a case
> > we could use
> > 
> > 	#address-cells = <2>;
> > 	...
> > 	subdev1 = {
> > 		reg = <1 1>; /* first client on pad 1 */
> > 	};
> > 
> > 	subdev2 = {
> > 		reg = <1 2>; /* second client on pad 1 */
> > 	};
> > 
> > But I'm not particularly attached to this idea. If we decide, that it's an
> > abuse, we can switch back to some property.
> 
> I think that would be an abuse :-)

It might well be, but I'd like to see a definitive opinion on this:)

> 
> My point was that a host represented by a single DT node might contain several 
> media entities. For instance the OMAP3 ISP contains two CSI2 receivers. Each 
> of them has a single sink pad, both numbered 0. The DT link representation 
> thus needs to mention which sink entity the sensor is connected to, in 
> addition to the pad number in that entity (and in the OMAP3 ISP case the pad 
> number could be omitted completely, as the CSI2 receivers have a single sink 
> pad).

On OMAP3 you could define #address-cells = <2> in the container node and 
use "reg = <0 0>" in links to specify entity and pad numbers. I looked 
briefly through some .dts in the kernel tree. There are a few uses of the 
reg property with just a single value like 0 or 1, but most of them do 
seem to have some physical meaning. The most obvious is the CPU number, 
then it's also used for pinctrl (not sure whether it's always justified 
there though), for eth phy's, also some weirder cases like ps/2 interface 
number (mouse / keyboard), ethernet instance, etc. So, basically, I'm fine 
either way. "reg" does seem to fulfill the role pretty nicely to me, but 
if the majority thinks it's an abuse, let's define our own property.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/