linux-kernel - Re: [PATCH net v3] ice: use proper macro for testing bit

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Date: Tue, 18 Jun 2024 15:43:57 +0200
From: Jiri Pirko <jiri@...nulli.us>
To: Petr Oros <poros@...hat.com>
Cc: netdev@...r.kernel.org, ivecera@...hat.com,
	przemyslaw.kitszel@...el.com, horms@...nel.org,
	Alexander Lobakin <aleksander.lobakin@...el.com>,
	Jesse Brandeburg <jesse.brandeburg@...el.com>,
	Tony Nguyen <anthony.l.nguyen@...el.com>,
	"David S. Miller" <davem@...emloft.net>,
	Eric Dumazet <edumazet@...gle.com>,
	Jakub Kicinski <kuba@...nel.org>, Paolo Abeni <pabeni@...hat.com>,
	Eric Joyner <eric.joyner@...el.com>,
	Marcin Domagala <marcinx.domagala@...el.com>,
	"moderated list:INTEL ETHERNET DRIVERS" <intel-wired-lan@...ts.osuosl.org>,
	open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net v3] ice: use proper macro for testing bit

Tue, Jun 18, 2024 at 01:11:19PM CEST, poros@...hat.com wrote:
>Do not use _test_bit() macro for testing bit. The proper macro for this
>is one without underline.
>
>_test_bit() is what test_bit() was prior to const-optimization. It
>directly calls arch_test_bit(), i.e. the arch-specific implementation
>(or the generic one). It's strictly _internal_ and shouldn't be used
>anywhere outside the actual test_bit() macro.
>
>test_bit() is a wrapper which checks whether the bitmap and the bit
>number are compile-time constants and if so, it calls the optimized
>function which evaluates this call to a compile-time constant as well.
>If either of them is not a compile-time constant, it just calls _test_bit().
>test_bit() is the actual function to use anywhere in the kernel.
>
>IOW, calling _test_bit() avoids potential compile-time optimizations.
>
>The sensors is not a compile-time constant, thus most probably there
>are no object code changes before and after the patch.
>But anyway, we shouldn't call internal wrappers instead of
>the actual API.
>
>Fixes: 4da71a77fc3b ("ice: read internal temperature sensor")
>Acked-by: Ivan Vecera <ivecera@...hat.com>
>Reviewed-by: Alexander Lobakin <aleksander.lobakin@...el.com>
>Signed-off-by: Petr Oros <poros@...hat.com>

Reviewed-by: Jiri Pirko <jiri@...dia.com>