Re: [PATCH 1/2] soundwire: bus: Prevent infinite loop in sdw_ch_mask_to_ch()

[Richard Fitzgerald]

On 03/02/2023 14:35, Pierre-Louis Bossart wrote:
> 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@xxxxxxxxxxxxxxxxxxxxx>
> > ---
> >   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;
> -}
> -

I'm happy to squash them, I did it in two steps so it didn't get
overlooked that there's a bugfix happening.