linux-kernel - Re: [PATCH v2 1/2] dt-bindings: Update iProc GPIO bindings

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Message-ID: <549befe2-9455-ab4b-0c91-d005d9993fdb@broadcom.com>
Date:	Wed, 11 May 2016 08:50:30 -0700
From:	Ray Jui <ray.jui@...adcom.com>
To:	Rob Herring <robh@...nel.org>
Cc:	Linus Walleij <linus.walleij@...aro.org>,
	Alexandre Courbot <gnurou@...il.com>,
	linux-kernel@...r.kernel.org, linux-gpio@...r.kernel.org,
	bcm-kernel-feedback-list@...adcom.com, devicetree@...r.kernel.org
Subject: Re: [PATCH v2 1/2] dt-bindings: Update iProc GPIO bindings

Hi Rob,

On 5/11/2016 7:06 AM, Rob Herring wrote:
> On Wed, May 04, 2016 at 09:29:04AM -0700, Ray Jui wrote:
>> Hi Rob,
>>
>> On 5/4/2016 6:20 AM, Rob Herring wrote:
>>> On Mon, May 02, 2016 at 01:51:47PM -0700, Ray Jui wrote:
>>>> Update the iProc GPIO binding document to add new compatible strings
>>>> "brcm,iproc-gpio-v2" and "brcm,iproc-gpio-v3" for the 2nd and 3rd
>>>> generation of the iProc GPIO controllers
>>>>
>>>> Signed-off-by: Ray Jui <ray.jui@...adcom.com>
>>>> ---
>>>> Documentation/devicetree/bindings/pinctrl/brcm,iproc-gpio.txt | 11 ++++++++++-
>>>> 1 file changed, 10 insertions(+), 1 deletion(-)
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/pinctrl/brcm,iproc-gpio.txt b/Documentation/devicetree/bindings/pinctrl/brcm,iproc-gpio.txt
>>>> index e427792..3a56649 100644
>>>> --- a/Documentation/devicetree/bindings/pinctrl/brcm,iproc-gpio.txt
>>>> +++ b/Documentation/devicetree/bindings/pinctrl/brcm,iproc-gpio.txt
>>>> @@ -4,7 +4,16 @@ Required properties:
>>>>
>>>> - compatible:
>>>>     Must be "brcm,cygnus-ccm-gpio", "brcm,cygnus-asiu-gpio",
>>>> -    "brcm,cygnus-crmu-gpio" or "brcm,iproc-gpio"
>>>> +    or "brcm,cygnus-crmu-gpio" for Cygnus SoCs
>>>> +
>>>> +    "brcm,iproc-gpio" for the first generation of the GPIO controller that
>>>> +    supports full-featured pinctrl and GPIO functions used in iProc based SoCs
>>>> +
>>>> +    "brcm,iproc-gpio-v2" for the second generation of the GPIO controller that
>>>> +    has the drive strength pinctrl support disabled, e.g., in the iProc NSP SoC
>>>> +
>>>> +    "brcm,iproc-gpio-v3" for the third generation of the GPIO controller that
>>>> +    has the general pinctrl support completely disabled
>>>
>>> You can have these for driver matching, but you still need SoC specific
>>> compatible strings.
>>>
>>> Rob
>>>
>>
>> I think I'm missing something and hope you can help to clarify here. It
>> looks like the notion of v2, v3 should only be used if there's an indeed an
>> revision update on the controller IP itself, correct?
>
> Yes, but only if v2, v3 is actually a meaningful number rather than
> something made up. You have to have a well defined process of IP
> revisions which I have not seen during my time in chip companies, so I'm
> generally suspicious of version numbers. The exception is FPGA IP
> blocks.
>
>> In our case, if the same revision of GPIO controller is used but instead
>> synthesized differently with different SoCs, then you are suggesting here
>> that it should be dealt with SoC specific compatible string, correct?
>
> Yes, that and/or integration differences is why you need SoC specific
> compatible strings. A block could be "identical" but have different max
> frequency for example.
>
>> For example, for the GPIO controller on NSP where drive strength is
>> disabled, the compatible string in DT should look like this?
>>
>> compatible = "brcm,iproc-gpio", "brcm,iproc-gpio-nsp";
>
> Yes, but reverse the order. Most specific to least specific.
>
>>
>> For the GPIO controller on Stingray where pinconf is completely disabled,
>> the compatible string in DT should look like:
>>
>> compatible = "brcm,iproc-gpio", "brcm,iproc-gpio-stingray";
>>
>> Is that correct?
>>
>> Thanks,
>>
>> Ray

Thanks for the clarification. I think I've got all the information I 
need. Will revise and send out PATCH v3 when I get a chance.

Thanks,

Ray