Re: [PATCH 3/3] ARM: OMAP2+: Add GPMC DT support for Ethernet child nodes

[Jon Hunter <jon-hunter@ti.com>]

On 03/14/2013 11:37 AM, Javier Martinez Canillas wrote:
> On Thu, Mar 14, 2013 at 4:48 PM, Jon Hunter <jon-hunter@ti.com> wrote:
>> Hi Javier,
>>
>> On 03/14/2013 10:09 AM, Javier Martinez Canillas wrote:
>>> Besides being used to interface with external memory devices,
>>> the General-Purpose Memory Controller can be used to connect
>>> Pseudo-SRAM devices such as ethernet controllers to OMAP2+
>>> processors using the TI GPMC as a data bus.
>>>
>>> This patch allows an ethernet chip to be defined as an GPMC
>>> child device node.
>>>
>>> Signed-off-by: Javier Martinez Canillas <javier.martinez@collabora.co.uk>
>>> ---
>>>  Documentation/devicetree/bindings/net/gpmc-eth.txt |   90 ++++++++++++++++++++
>>>  arch/arm/mach-omap2/gpmc.c                         |    8 ++
>>>  2 files changed, 98 insertions(+), 0 deletions(-)
>>>  create mode 100644 Documentation/devicetree/bindings/net/gpmc-eth.txt
>>>
>>> diff --git a/Documentation/devicetree/bindings/net/gpmc-eth.txt b/Documentation/devicetree/bindings/net/gpmc-eth.txt
>>> new file mode 100644
>>> index 0000000..c45363c
>>> --- /dev/null
>>> +++ b/Documentation/devicetree/bindings/net/gpmc-eth.txt
>>> @@ -0,0 +1,90 @@
>>> +Device tree bindings for Ethernet chip connected to TI GPMC
>>> +
>>> +Besides being used to interface with external memory devices, the
>>> +General-Purpose Memory Controller can be used to connect Pseudo-SRAM devices
>>> +such as ethernet controllers to processors using the TI GPMC as a data bus.
>>> +
>>> +Ethernet controllers connected to TI GPMC are represented as child nodes of
>>> +the GPMC controller with an "ethernet" name.
>>> +
>>> +All timing relevant properties as well as generic GPMC child properties are
>>> +explained in a separate documents. Please refer to
>>> +Documentation/devicetree/bindings/bus/ti-gpmc.txt
>>> +
>>> +Required properties:
>>> +- bank-width:                Address width of the device in bytes. GPMC supports 8-bit
>>> +                     and 16-bit devices and so must be either 1 or 2 bytes.
>>
>> I am wondering if we should use reg-io-width here. The smsc driver is
>> using this to determine the width of the device. And so I am wondering
>> if this could cause problems.
>>
>> Obviously this complicates gpmc_probe_generic_child() a little, but may
>> be would could pass the name of the width property to
>> gpmc_probe_generic_child() as well. What do you think?
>>
> 
> Hi Jon,
> 
> Well now I'm confused. I thought that both were needed since a
> combination of bank-width 16-bit / reg-io-width 32-bit is also
> possible (in fact that is how I'm testing on my IGEPv2) and we have
> talked about this before [1].

Yes you are right. Sorry about that ...

> By reading both the OMAP3 TRM and the smsc LAN9221 data-sheet, it
> seems that the reg-io-width is not about the data bus address width
> but the CPU address width. The smsc data-sheet says:
> 
> "The simple, yet highly functional host bus interface provides a
> glue-less connection to most common 16-bit microprocessors and
> microcontrollers as well as 32-bit microprocessors with a 16-bit
> external bus"
> 
> By looking at the smsc911x driver
> (drivers/net/ethernet/smsc/smsc911x.c) I see that if you use
> reg-io-width = <4> (SMSC911X_USE_32BIT) then the smsc911x hardware
> registers can be read in one operation and if you use reg-io-width =
> <2> (SMSC911X_USE_16BIT) then you need two operations to read the
> register:
> 
> static inline u32 __smsc911x_reg_read(struct smsc911x_data *pdata, u32 reg)
> {
> 	if (pdata->config.flags & SMSC911X_USE_32BIT)
> 		return readl(pdata->ioaddr + reg);
> 
> 	if (pdata->config.flags & SMSC911X_USE_16BIT)
> 		return ((readw(pdata->ioaddr + reg) & 0xFFFF) |
> 			((readw(pdata->ioaddr + reg + 2) & 0xFFFF) << 16));
> 
> 	BUG();
> 	return 0;
> }

Looking at the above, then I don't see any issue with this then.

> Also, by reading at the OMAP3 TRM, I understand that even when the
> GPMC has a maximum 16-bit address width, it support devices that has
> 32-bit registers by doing some sort of access adaptation.

Yes I believe that is correct.

> So, as far as I understand the "bank-width" is to configure the GPMC
> if is going to use a 8-bit or 16-bit width access and the
> "reg-io-width" is how the smsc911x driver is going to read its
> registers. So, I think we need both properties and there is no need to
> change gpmc_probe_generic_child() neither pass the child name to it.
> 
> But to be honest I can be wrong here since data-sheet and technical
> reference manuals can be quite confusing sometimes :-)

Ok, so do you think that we should add some documentation to the
gpmc-eth.txt so say that set "reg-io-width = <4>;" for OMAP regardless
of bank-width?

Cheers
Jon