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From: Ping-Ke Shih <pkshih@realtek.com>
To: Su Hui <suhui@nfschina.com>,
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Subject: RE: [PATCH v2 2/2] wifi: rtlwifi: rtl8821ae: phy: fix an undefined bitwise shift behavior
Thread-Topic: [PATCH v2 2/2] wifi: rtlwifi: rtl8821ae: phy: fix an undefined
 bitwise shift behavior
Thread-Index: AQHaHnqh3ek0X9cmrkSIvDKQ0v3B9rCJKRKA
Date: Fri, 24 Nov 2023 08:51:15 +0000
Message-ID: <167fbc7a77db447d90f696666f6f0a9b@realtek.com>
References: <20231124020352.1660621-1-suhui@nfschina.com>
 <20231124020352.1660621-2-suhui@nfschina.com>
In-Reply-To: <20231124020352.1660621-2-suhui@nfschina.com>
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> -----Original Message-----
> From: Su Hui <suhui@nfschina.com>
> Sent: Friday, November 24, 2023 10:04 AM
> To: dan.carpenter@linaro.org; Ping-Ke Shih <pkshih@realtek.com>; kvalo@ke=
rnel.org; nathan@kernel.org;
> ndesaulniers@google.com; trix@redhat.com
> Cc: Su Hui <suhui@nfschina.com>; lizetao1@huawei.com; linville@tuxdriver.=
com; Larry.Finger@lwfinger.net;
> linux-wireless@vger.kernel.org; linux-kernel@vger.kernel.org; llvm@lists.=
linux.dev;
> kernel-janitors@vger.kernel.org
> Subject: [PATCH v2 2/2] wifi: rtlwifi: rtl8821ae: phy: fix an undefined b=
itwise shift behavior
>=20

[...]

>=20
> diff --git a/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c
> b/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c
> index 6df270e29e66..52ab1b0761c0 100644
> --- a/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c
> +++ b/drivers/net/wireless/realtek/rtlwifi/rtl8821ae/phy.c
> @@ -31,7 +31,12 @@ static u32 _rtl8821ae_phy_calculate_bit_shift(u32 bitm=
ask)
>  {
>         u32 i =3D ffs(bitmask);
>=20
> -       return i ? i - 1 : 32;
> +       if (!i) {
> +               WARN_ON_ONCE(1);
> +               return 0;
> +       }
> +
> +       return i - 1;
>  }

Personally, I prefer to use __ffs(), because in normal case no need additio=
nal '-1',
and abnormal cases should not happen.=20