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From:   Ping-Ke Shih <pkshih@realtek.com>
To:     Dan Carpenter <error27@gmail.com>
CC:     "linux-wireless@vger.kernel.org" <linux-wireless@vger.kernel.org>
Subject: RE: [bug report] rtw89: add Realtek 802.11ax driver
Thread-Topic: [bug report] rtw89: add Realtek 802.11ax driver
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Date:   Tue, 13 Dec 2022 00:46:22 +0000
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> -----Original Message-----
> From: Dan Carpenter <error27@gmail.com>
> Sent: Monday, December 12, 2022 11:34 PM
> To: Ping-Ke Shih <pkshih@realtek.com>
> Cc: linux-wireless@vger.kernel.org
> Subject: [bug report] rtw89: add Realtek 802.11ax driver
> 
> Hello Ping-Ke Shih,
> 
> The patch e3ec7017f6a2: "rtw89: add Realtek 802.11ax driver" from Oct
> 11, 2021, leads to the following potential issue (just from reading
> the code):
> 
> drivers/net/wireless/realtek/rtw89/core.h
>     3878 static inline u32
>     3879 rtw89_read32_mask(struct rtw89_dev *rtwdev, u32 addr, u32 mask)
>     3880 {
>     3881         u32 shift = __ffs(mask);
>     3882         u32 orig;
>     3883         u32 ret;
>     3884
>     3885         orig = rtw89_read32(rtwdev, addr);
> --> 3886         ret = (orig & mask) >> shift;
> 
> I think this line should be:
> 
> 	ret = (orig & mask) >> (shift - 1);
> 
> A typical mask here is 0xff so __ffs() is 1 because the first bit is
> set.  This code will do: ret = (orig & 0xff) >> 1;  I think it should be
> ret = (orig & 0xff) >> 0;
> 
> If the mask was 0xff00 I would expect >> 8 instead of >> 9 etc.

ffs(0xff)=1 and __ffs(0xff)=0, so I think original is correct.

Ping-Ke