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Subject: Re: [PATCH] bitfield: suppress "dubious: x & !y" sparse warning
From: Kalle Valo <kvalo@kernel.org>
In-Reply-To: 
 <20240223100146.d243b6b1a9a1.I033828b1187c6bccf086e31400f7e933bb8373e7@changeid>
References: 
 <20240223100146.d243b6b1a9a1.I033828b1187c6bccf086e31400f7e933bb8373e7@changeid>
To: Johannes Berg <johannes@sipsolutions.net>
Cc: linux-wireless@vger.kernel.org, Felix Fietkau <nbd@nbd.name>,
 Jeff Johnson <jjohnson@kernel.org>, ath11k@lists.infradead.org,
 Johannes Berg <johannes.berg@intel.com>
User-Agent: pwcli/0.1.1-git (https://github.com/kvalo/pwcli/) Python/3.11.2
Message-ID: <170912125112.3868947.18107049542995601682.kvalo@kernel.org>
Date: Wed, 28 Feb 2024 11:54:12 +0000 (UTC)

Johannes Berg <johannes@sipsolutions.net> wrote:

> From: Johannes Berg <johannes.berg@intel.com>
> 
> There's a somewhat common pattern of using FIELD_PREP()
> even for single bits, e.g.
> 
>  cmd->info1 |= FIELD_PREP(HTT_SRNG_SETUP_CMD_INFO1_RING_FLAGS_MSI_SWAP,
>                           !!(params.flags & HAL_SRNG_FLAGS_MSI_SWAP));
> 
> which might as well be written as
> 
>  if (params.flags & HAL_SRNG_FLAGS_MSI_SWAP)
>    cmd->info1 |= HTT_SRNG_SETUP_CMD_INFO1_RING_FLAGS_MSI_SWAP;
> 
> (since info1 is fully initialized to start with), but in
> a long chain of FIELD_PREP() this really seems fine.
> 
> However, it triggers a sparse warning, in the check in
> the macro for whether a constant value fits into the mask,
> as this contains a "& (_val)". In this case, this really
> is always intentional, so just suppress the warning by
> adding "0+" to the expression, indicating explicitly that
> this is correct.
> 
> Signed-off-by: Johannes Berg <johannes.berg@intel.com>

Patch applied to wireless-next.git, thanks.

416eb60317c6 bitfield: suppress "dubious: x & !y" sparse warning

-- 
https://patchwork.kernel.org/project/linux-wireless/patch/20240223100146.d243b6b1a9a1.I033828b1187c6bccf086e31400f7e933bb8373e7@changeid/

https://wireless.wiki.kernel.org/en/developers/documentation/submittingpatches