linux-kernel - Re: [RFC PATCH 1/2] of: Add a variant of of_device_is_compatible() that can be build time culled

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Message-ID: <20260108233818.GA1466897-robh@kernel.org>
Date: Thu, 8 Jan 2026 17:38:18 -0600
From: Rob Herring <robh@...nel.org>
To: Daniel Palmer <daniel@...ngy.jp>
Cc: linusw@...nel.org, brgl@...nel.org, saravanak@...nel.org,
	linux-gpio@...r.kernel.org, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/2] of: Add a variant of of_device_is_compatible()
 that can be build time culled

On Wed, Jan 07, 2026 at 12:07:30PM +0900, Daniel Palmer wrote:
> In a lot of places we are using of_device_is_compatible() to check for quirks

I'm assuming 'a lot' is not just 3 places? Got a rough estimate?

This seems fine to me assuming there are more.

> etc that are simply not possible on some targets, i.e. a piece of hardware
> that needs special handling is only on one specific ARM machine and your
> target isn't even ARM.
> 
> Add of_device_is_possible_and_compatible() that also takes a Kconfig
> symbol and checks if that is enabled before calling of_device_is_compatible().
> 
> The Kconfig symbol is build time constant and the compiler should
> remove the call to of_device_is_compatible() if it is unneeded and also
> remove the data for the compatible string.
> 
> Another merit of this is that in places were we are checking for quirks
> outside of drivers themselves, i.e. in the gpio and spi subsystems where
> some legacy devicetree handling is being handled for specific devices
> is in the core code, when the drivers that need the quirks are removed
> their Kconfig symbol should also be removed and it'll be easier to spot
> that the quirk handling can also go.
> 
> Signed-off-by: Daniel Palmer <daniel@...ngy.jp>
> ---
>  include/linux/of.h | 2 ++
>  1 file changed, 2 insertions(+)
> 
> diff --git a/include/linux/of.h b/include/linux/of.h
> index 9bbdcf25a2b4..70be20b0be22 100644
> --- a/include/linux/of.h
> +++ b/include/linux/of.h
> @@ -358,6 +358,8 @@ extern int of_property_read_string_helper(const struct device_node *np,
>  					      const char **out_strs, size_t sz, int index);
>  extern int of_device_is_compatible(const struct device_node *device,
>  				   const char *);
> +#define of_device_is_possible_and_compatible(symbol, device, string) \
> +	(IS_ENABLED(symbol) && of_device_is_compatible(device, string))
>  extern int of_device_compatible_match(const struct device_node *device,
>  				      const char *const *compat);
>  extern bool of_device_is_available(const struct device_node *device);
> -- 
> 2.51.0
>