linux-kernel - Re: [PATCH V3 2/6] dt-bindings: timestamp: Add Tegra234 support

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Message-ID: <6c5045d9-4f4a-5018-3f3f-7746b08ab2b5@linaro.org>
Date:   Mon, 13 Mar 2023 18:55:45 +0100
From:   Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>
To:     Dipen Patel <dipenp@...dia.com>, 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, robh+dt@...nel.org,
        timestamp@...ts.linux.dev, krzysztof.kozlowski+dt@...aro.org,
        brgl@...ev.pl, corbet@....net, gregkh@...uxfoundation.org
Subject: Re: [PATCH V3 2/6] dt-bindings: timestamp: Add Tegra234 support

On 13/03/2023 18:05, Dipen Patel wrote:
> On 3/12/23 8:47 AM, Krzysztof Kozlowski wrote:
>> On 10/03/2023 20:06, Dipen Patel wrote:
>>> Added timestamp provider support for the Tegra234 in devicetree
>>> bindings. In addition, it addresses review comments from the
>>> previous review round as follows:
>>> - Removes nvidia,slices property. This was not necessary as it
>>> is a constant value and can be hardcoded inside the driver code.
>>> - Adds nvidia,gpio-controller property. This simplifies how GTE driver
>>> retrieves GPIO controller instance, see below explanation.
>>>
>>> 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;
>>>
>>> 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);
>>>
>>> We haven't technically started making use of these bindings, so
>>> backwards-compatibility shouldn't be an issue yet.
>>
>> Unfortunately, I don't understand this statement. The
>> nvidia,tegra194-gte-aon with removed property is in a released kernel
>> v6.2. What does it mean "technically"? It's a released kernel thus it is
>> a released ABI.
> 
> There is no active user of that driver, so even if it breaks 6.2, it is fine
> as there is no one to complain about it.

How do you know? It's a released kernel, thus how can you ask millions
of people if they use it or not?

Best regards,
Krzysztof