linux-kernel - Re: [PATCH 10/10] of/device: Don't NULLify match table in of_match_device() with CONFIG

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Date:   Thu, 17 Oct 2019 12:47:59 -0500
From:   Frank Rowand <frowand.list@...il.com>
To:     Stephen Boyd <swboyd@...omium.org>, linux-kernel@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>
Cc:     Arnd Bergmann <arnd@...db.de>,
        Geert Uytterhoeven <geert@...ux-m68k.org>
Subject: Re: [PATCH 10/10] of/device: Don't NULLify match table in
 of_match_device() with CONFIG_OF=n

On 10/04/2019 16:43, Stephen Boyd wrote:
> This effectively reverts 1db73ae39a97 ("of/device: Nullify match table
> in of_match_device() for CONFIG_OF=n") because that commit makes it more
> surprising to users of this API that the arguments may never be
> referenced by any code. This is because the pre-processor will replace
> the argument with NULL and then the match table will be left unreferenced
> by any code but the compiler optimizer doesn't know to drop it. This can
> lead to compilers warning that match tables are unused, when we really
> want to pass the match table to the API but have the compiler see that
> it's all inlined and not used and then drop the match table while
> silencing the warning. We're being too smart here and not giving the
> compiler the chance to do dead code elimination.
> 
> Cc: Arnd Bergmann <arnd@...db.de>
> Cc: Geert Uytterhoeven <geert@...ux-m68k.org>
> Cc: Rob Herring <robh+dt@...nel.org>
> Cc: Frank Rowand <frowand.list@...il.com>
> Signed-off-by: Stephen Boyd <swboyd@...omium.org>
> ---
> 
> Please ack or pick for immediate merge so the last patch can be merged.
> 
>  include/linux/of_device.h | 4 +---
>  1 file changed, 1 insertion(+), 3 deletions(-)
> 
> diff --git a/include/linux/of_device.h b/include/linux/of_device.h
> index 8d31e39dd564..3f8ca55bc693 100644
> --- a/include/linux/of_device.h
> +++ b/include/linux/of_device.h
> @@ -93,13 +93,11 @@ static inline int of_device_uevent_modalias(struct device *dev,
>  
>  static inline void of_device_node_put(struct device *dev) { }
>  
> -static inline const struct of_device_id *__of_match_device(
> +static inline const struct of_device_id *of_match_device(
>  		const struct of_device_id *matches, const struct device *dev)
>  {
>  	return NULL;
>  }
> -#define of_match_device(matches, dev)	\
> -	__of_match_device(of_match_ptr(matches), (dev))
>  
>  static inline struct device_node *of_cpu_device_node_get(int cpu)
>  {
> 


Acked-by: Frank Rowand <frowand.list@...il.com>