Use of pinctrl-single for external device over I2C

Use of pinctrl-single for external device over I2C

[Vaibhav Hiremath]

On Tuesday 23 June 2015 04:25 PM, Vaibhav Hiremath wrote:
> Hi,

+ linux-arm-kernel & MFD

Thanks,
Vaibhav
>
> I am working on enabling support for PMIC 88PM860 device in the
> mainline.
>
> In 88PM860 (and family of devices) few pins are labelled as GPIO's, to
> be precise, in 88PM860, we have 8 GPIO's (ana & dig).
>
>
> I was looking at pinctrl-single driver, as it seems it can not handle
> pinmux configuration of external device (in this case its over I2C), as
> it uses raw read/write api's.
>
> I see below lines in the driver,
>
>
> /*
>   * REVISIT: Reads and writes could eventually use regmap or something
>   * generic. But at least on omaps, some mux registers are performance
>   * critical as they may need to be remuxed every time before and after
>   * idle. Adding tests for register access width for every read and
>   * write like regmap is doing is not desired, and caching the registers
>   * does not help in this case.
>   */
>
>
> Should be not have flag for this and use regmap_ variants? If we
> implement flag based approach then same driver can be reused for pinmux
> configuration of external device.
>
>
> Just to give more clarity, Let me describe my use-case below,
>
> The platform which I have is based on PXA1928 and 88PM860 chipsets,
> where 88PM860.GPIO_0 is connected back to PXA1928.EXT_32K_IN.
>
> GPIO_0 need to configured in mode '4'.
>
> As per spec, 88PM860.GPIO_0 can be configured to
>
>   000 = GPIO input mode
>   001 = GPIO output mode
>   010 = SLEEPOUTN mirror mode
>   011 = Buck4 FPWM enable
>   100 = 32 Khz output buffer mode
>   101 = PMICINTN output mode
>   110 = HW_RESET1 mode
>   111 = HW_RESET2 mode
>
>
> Please let me know if there is already an alternative for this, which I
> missed.
>
> Thanks,
> Vaibhav
>
>
>
> Thanks,
> Vaibhav

Use of pinctrl-single for external device over I2C

[Tony Lindgren]

* Vaibhav Hiremath <vaibhav.hiremath@linaro.org> [150624 05:06]:
> On Tuesday 23 June 2015 04:25 PM, Vaibhav Hiremath wrote:
> >
> >/*
> >  * REVISIT: Reads and writes could eventually use regmap or something
> >  * generic. But at least on omaps, some mux registers are performance
> >  * critical as they may need to be remuxed every time before and after
> >  * idle. Adding tests for register access width for every read and
> >  * write like regmap is doing is not desired, and caching the registers
> >  * does not help in this case.
> >  */
> >
> >
> >Should be not have flag for this and use regmap_ variants? If we
> >implement flag based approach then same driver can be reused for pinmux
> >configuration of external device.

Nothing stopping you from adding regmap support to it. It just needs
to be made optional as the users so far don't need it.

Regards,

Tony

Use of pinctrl-single for external device over I2C

[Vaibhav Hiremath]

On Wednesday 24 June 2015 07:03 PM, Tony Lindgren wrote:
> * Vaibhav Hiremath <vaibhav.hiremath@linaro.org> [150624 05:06]:
>> On Tuesday 23 June 2015 04:25 PM, Vaibhav Hiremath wrote:
>>>
>>> /*
>>>   * REVISIT: Reads and writes could eventually use regmap or something
>>>   * generic. But at least on omaps, some mux registers are performance
>>>   * critical as they may need to be remuxed every time before and after
>>>   * idle. Adding tests for register access width for every read and
>>>   * write like regmap is doing is not desired, and caching the registers
>>>   * does not help in this case.
>>>   */
>>>
>>>
>>> Should be not have flag for this and use regmap_ variants? If we
>>> implement flag based approach then same driver can be reused for pinmux
>>> configuration of external device.
>
> Nothing stopping you from adding regmap support to it. It just needs
> to be made optional as the users so far don't need it.
>

Yeah, absolutely.

Thinking more on this,


I do not like this, as this is not HW feature, so DT may not be right
approach.


So I will dig more from either runtime or Compile time option to use
regmap_ Vs raw read/writes.


Thanks,
Vaibhav

Use of pinctrl-single for external device over I2C

[Tony Lindgren]

* Vaibhav Hiremath <vaibhav.hiremath@linaro.org> [150624 10:12]:
> 
> I do not like this, as this is not HW feature, so DT may not be right
> approach.
> 
> So I will dig more from either runtime or Compile time option to use
> regmap_ Vs raw read/writes.

Can't you just check if the pinctrl node has compatible = "syscon"
property?

A compile time option won't work for sure. I don't know what you
would check at runtime as you do not know what the bus is behind
syscon.

Regards,

Tony

Use of pinctrl-single for external device over I2C

[Vaibhav Hiremath]

On Thursday 25 June 2015 10:08 AM, Tony Lindgren wrote:
> * Vaibhav Hiremath <vaibhav.hiremath@linaro.org> [150624 10:12]:
>>
>> I do not like this, as this is not HW feature, so DT may not be right
>> approach.
>>
>> So I will dig more from either runtime or Compile time option to use
>> regmap_ Vs raw read/writes.
>
> Can't you just check if the pinctrl node has compatible = "syscon"
> property?
>
> A compile time option won't work for sure. I don't know what you
> would check at runtime as you do not know what the bus is behind
> syscon.
>

Although, I haven't gone through syscon, but not sure whether syscon
would be useful.

As you rightly stated, we need to know the bus behind regmap.

Thanks,
Vaibhav

Use of pinctrl-single for external device over I2C

[Vaibhav Hiremath]

On Thursday 25 June 2015 11:16 AM, Vaibhav Hiremath wrote:
>
>
> On Thursday 25 June 2015 10:08 AM, Tony Lindgren wrote:
>> * Vaibhav Hiremath <vaibhav.hiremath@linaro.org> [150624 10:12]:
>>>
>>> I do not like this, as this is not HW feature, so DT may not be right
>>> approach.
>>>
>>> So I will dig more from either runtime or Compile time option to use
>>> regmap_ Vs raw read/writes.
>>
>> Can't you just check if the pinctrl node has compatible = "syscon"
>> property?
>>
>> A compile time option won't work for sure. I don't know what you
>> would check at runtime as you do not know what the bus is behind
>> syscon.
>>
>
> Although, I haven't gone through syscon, but not sure whether syscon
> would be useful.
>
> As you rightly stated, we need to know the bus behind regmap.
>

Trying to understand what is the right way of doing pinctrl of external
device on board,

I feel it would not be good idea to pollute pinctrl-single driver, and 
also I am still not able to figure out how can I have access to bus
behind regmap.


How about having separate driver (generic for all I2C), say pinctrl-
i2c.c, which is i2c_client driver and would support pinctrl and pinmux
on I2C client device.


The current usecase which I have is pretty simple in nature,

88PM860 has few GPIO pins which can be configured to different
functionality, based on board design.
In most of the cases they are one/init/boot time settings.

GPIO_0:
=======
   000 = GPIO input mode
   001 = GPIO output mode
   010 = SLEEPOUTN mirror mode
   011 = Buck4 FPWM enable
   100 = 32 Khz output buffer mode
   101 = PMICINTN output mode
   110 = HW_RESET1 mode
   111 = HW_RESET2 mode


Thanks,
Vaibhav

Use of pinctrl-single for external device over I2C

[Vaibhav Hiremath]

On Tuesday 30 June 2015 01:16 PM, Vaibhav Hiremath wrote:
>
>
> On Thursday 25 June 2015 11:16 AM, Vaibhav Hiremath wrote:
>>
>>
>> On Thursday 25 June 2015 10:08 AM, Tony Lindgren wrote:
>>> * Vaibhav Hiremath <vaibhav.hiremath@linaro.org> [150624 10:12]:
>>>>
>>>> I do not like this, as this is not HW feature, so DT may not be right
>>>> approach.
>>>>
>>>> So I will dig more from either runtime or Compile time option to use
>>>> regmap_ Vs raw read/writes.
>>>
>>> Can't you just check if the pinctrl node has compatible = "syscon"
>>> property?
>>>
>>> A compile time option won't work for sure. I don't know what you
>>> would check at runtime as you do not know what the bus is behind
>>> syscon.
>>>
>>
>> Although, I haven't gone through syscon, but not sure whether syscon
>> would be useful.
>>
>> As you rightly stated, we need to know the bus behind regmap.
>>
>
> Trying to understand what is the right way of doing pinctrl of external
> device on board,
>
> I feel it would not be good idea to pollute pinctrl-single driver, and
> also I am still not able to figure out how can I have access to bus
> behind regmap.
>
>
> How about having separate driver (generic for all I2C), say pinctrl-
> i2c.c, which is i2c_client driver and would support pinctrl and pinmux
> on I2C client device.
>

I mean, part of mfd here (mfd_cell)

>
> The current usecase which I have is pretty simple in nature,
>
> 88PM860 has few GPIO pins which can be configured to different
> functionality, based on board design.
> In most of the cases they are one/init/boot time settings.
>
> GPIO_0:
> =======
>    000 = GPIO input mode
>    001 = GPIO output mode
>    010 = SLEEPOUTN mirror mode
>    011 = Buck4 FPWM enable
>    100 = 32 Khz output buffer mode
>    101 = PMICINTN output mode
>    110 = HW_RESET1 mode
>    111 = HW_RESET2 mode
>
>
> Thanks,
> Vaibhav