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

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Date:   Tue, 4 Apr 2023 12:28:49 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Dipen Patel <dipenp@...dia.com>
Cc:     Krzysztof Kozlowski <krzysztof.kozlowski@...aro.org>,
        Rob Herring <robh@...nel.org>, 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 Mon, Apr 03, 2023 at 09:24:17PM -0700, Dipen Patel wrote:
> On 3/25/23 4:09 AM, Krzysztof Kozlowski wrote:
> > 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.
> 
> Perhaps I should not have mentioned driver related details here about how
> this property will help, that detail will go in driver patch. In the next
> patch series I will remove this commit and just focus on what this property
> is.

I think the point that Rob and Krzysztof are trying to make that rather
than adding a new property for this, we can add a const char *gpio field
to struct tegra_hte_data and then set that to the compatible string of
the GPIO controller that we need this for.

To be honest, I slightly prefer the explicit phandle reference, but it
also complicates things a bit and looking up by compatible string isn't
all that bad.

Thierry

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