linux-kernel - Re: [PATCH 1/2] soundwire: bus: Prevent infinite loop in sdw_ch_mask_to

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Date:   Fri, 3 Feb 2023 08:35:11 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Richard Fitzgerald <rf@...nsource.cirrus.com>, vkoul@...nel.org,
        yung-chuan.liao@...ux.intel.com, sanyog.r.kale@...el.com
Cc:     alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        patches@...nsource.cirrus.com
Subject: Re: [PATCH 1/2] soundwire: bus: Prevent infinite loop in
 sdw_ch_mask_to_ch()



On 2/2/23 09:42, Richard Fitzgerald wrote:
> Define the ch_mask argument of sdw_ch_mask_to_ch() as an unsigned
> so that the shift right is guaranteed to eventually make the
> value of ch_mask==0.
> 
> Previously ch_mask was defined as a signed int, but a right
> shift of a signed value preserves the sign bit. So if the sign
> bit was 1, ch_mask would never become 0 and the for loop would
> be infinite.
> Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
> ---
>  drivers/soundwire/bus.h | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/soundwire/bus.h b/drivers/soundwire/bus.h
> index 7631ef5e71fb..28bedc919b78 100644
> --- a/drivers/soundwire/bus.h
> +++ b/drivers/soundwire/bus.h
> @@ -160,7 +160,7 @@ int sdw_fill_msg(struct sdw_msg *msg, struct sdw_slave *slave,
>  		 u32 addr, size_t count, u16 dev_num, u8 flags, u8 *buf);
>  
>  /* Retrieve and return channel count from channel mask */
> -static inline int sdw_ch_mask_to_ch(int ch_mask)
> +static inline int sdw_ch_mask_to_ch(unsigned int ch_mask)
>  {
>  	int c = 0;
>  

This patch1 is fine, but you remove this function in patch2, so is this
patch needed at all?

-/* Retrieve and return channel count from channel mask */
-static inline int sdw_ch_mask_to_ch(unsigned int ch_mask)
-{
-	int c = 0;
-
-	for (c = 0; ch_mask; ch_mask >>= 1)
-		c += ch_mask & 1;
-
-	return c;
-}
-