linux-kernel - Re: [PATCH V4 04/10] dt-bindings: timestamp: Add nvidia,gpio-controller

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Message-ID: <19b71fef-614a-d678-2e73-95db8f226e61@linaro.org>
Date:   Sat, 25 Mar 2023 12:09:51 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Dipen Patel <dipenp@...dia.com>, Rob Herring <robh@...nel.org>
Cc:     thierry.reding@...il.com, jonathanh@...dia.com,
        linux-kernel@...r.kernel.org, linux-tegra@...r.kernel.org,
        linux-gpio@...r.kernel.org, linus.walleij@...aro.org,
        devicetree@...r.kernel.org, linux-doc@...r.kernel.org,
        timestamp@...ts.linux.dev, krzysztof.kozlowski+dt@...aro.org,
        brgl@...ev.pl, corbet@....net, gregkh@...uxfoundation.org
Subject: Re: [PATCH V4 04/10] dt-bindings: timestamp: Add
 nvidia,gpio-controller

On 24/03/2023 19:51, Dipen Patel wrote:
> On 3/24/23 10:13 AM, Rob Herring wrote:
>> On Wed, Mar 22, 2023 at 06:29:23PM -0700, Dipen Patel wrote:
>>> Introducing nvidia,gpio-controller property from Tegra234 SoCs onwards.
>>> This is done to help below case.
>>>
>>> Without this property code would look like:
>>> if (of_device_is_compatible(dev->of_node, "nvidia,tegra194-gte-aon"))
>>> 	hte_dev->c = gpiochip_find("tegra194-gpio-aon",
>>> 				   tegra_get_gpiochip_from_name);
>>> else if (of_device_is_compatible(dev->of_node, "nvidia,tegra234-gte-aon"))
>>> 	hte_dev->c = gpiochip_find("tegra234-gpio-aon",
>>> 				   tegra_get_gpiochip_from_name);
>>> else
>>> 	return -ENODEV;
>>
>> Or you just put the name in match data.
> 
> Not sure I have understood this comment, but "name" the first argument is
> already there to supply to callback to match data. Also, this if else is
> needed to know which "name" to provide.

The point is that of_device_is_compatible() do not really scale and make
code more difficult to read. Your variant-customization should in
general entirely come from match/driver data.


>>
>>>
>>> This means for every future addition of the compatible string, if else
>>> condition statements have to be expanded.
>>>
>>> With the property:
>>> gpio_ctrl = of_parse_phandle(dev->of_node, "nvidia,gpio-controller", 0);
>>> ....
>>> hte_dev->c = gpiochip_find(gpio_ctrl, tegra_get_gpiochip_from_of_node);
>>>
>>> This simplifies the code significantly. The introdunction of this
>>
>> typo
> 
> ACK...
>>
>>> property/binding does not break existing Tegra194 provider driver.
>>
>> Making a new property required is an ABI break.
> The driver code for the Tegra194 binds by old binding and does not need
> this new property, the relevant code is part of this patch series.
>>
>>> Signed-off-by: Dipen Patel <dipenp@...dia.com>
>>> ---
>>>  .../timestamp/nvidia,tegra194-hte.yaml        | 31 +++++++++++++++++--
>>>  1 file changed, 29 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/Documentation/devicetree/bindings/timestamp/nvidia,tegra194-hte.yaml b/Documentation/devicetree/bindings/timestamp/nvidia,tegra194-hte.yaml
>>> index eafc33e9ae2e..841273a3d8ae 100644
>>> --- a/Documentation/devicetree/bindings/timestamp/nvidia,tegra194-hte.yaml
>>> +++ b/Documentation/devicetree/bindings/timestamp/nvidia,tegra194-hte.yaml
>>> @@ -51,6 +51,12 @@ properties:
>>>        LIC instance has 11 slices and Tegra234 LIC has 17 slices.
>>>      enum: [3, 11, 17]
>>>  
>>> +  nvidia,gpio-controller:
>>> +    $ref: /schemas/types.yaml#/definitions/phandle
>>> +    description:
>>> +      The phandle to AON gpio controller instance. This is required to handle
>>> +      namespace conversion between GPIO and GTE.
>>
>> Explain what the GPIO controller is needed for rather than how this 
>> changes the driver.
> Doesn't "This is required..." statement addresses why GPIO controller is needed
> for part? Or do you want detail explanation which is already part of the commit?

Your bindings commit msg focused on driver and it is not really what it
should be about.

Best regards,
Krzysztof