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

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Message-ID: <f6d9c84a-1c75-d9b4-59ed-39d6c5b310a9@linaro.org>
Date:   Sun, 12 Mar 2023 16:47:29 +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 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.

And since DTS always go to separate branch, your patch #4 breaks
existing DTS (return -ENODEV;) - it is not bisectable.

> 
> Signed-off-by: Dipen Patel <dipenp@...dia.com>
> ---


Best regards,
Krzysztof