RE: Re: [PATCH] ASoC: fsl_sai: Fix 32 slots TDM broken by integer shift UB in xMR write

quoted

When configuring 32 slots TDM (channels == slots == 32), the xMR (Mask
Register) write used:
~0UL - ((1 << min(channels, slots)) - 1)

The literal '1' is a signed 32-bit int. Shifting it by 32 positions is
undefined behaviour which may set this register to 0xFFFFFFFF, masking
all 32 slots.

Use 1ULL so the shift is carried out in 64 bits. For 32 slots this
produces a zero mask after truncation to the 32-bit register:
~0ULL - ((1ULL << 32) - 1)
   = 0xFFFFFFFFFFFFFFFF - (0x100000000 - 1)
   = 0xFFFFFFFFFFFFFFFF - 0xFFFFFFFF
   = 0xFFFFFFFF00000000
   -> Truncates to 0x00000000
Behaviour for fewer than 32 slots is unchanged.

Why not use macro GENMASK_U32() instead ?

Thanks for this reminder. OK, I will switch to the clearer and safer
GENMASK_U32() macro:
	regmap_write(sai->regmap, FSL_SAI_xMR(tx),
		     ~GENMASK_U32(min(channels, slots) - 1, 0));

Regards, 
Chancel Liu

quoted

Fixes: 770f58d7d2c5 ("ASoC: fsl_sai: Support multiple data channel
enable bits")
Cc: stable@vger.kernel.org
Signed-off-by: Chancel Liu <redacted>
---
  sound/soc/fsl/fsl_sai.c | 2 +-
  1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/sound/soc/fsl/fsl_sai.c b/sound/soc/fsl/fsl_sai.c index

d6dd95680892..821e3bd51b6e 100644

--- a/sound/soc/fsl/fsl_sai.c
+++ b/sound/soc/fsl/fsl_sai.c

@@ -797,7 +797,7 @@ static int fsl_sai_hw_params(struct

snd_pcm_substream *substream,

quoted

                                 FSL_SAI_CR4_FSD_MSTR,
FSL_SAI_CR4_FSD_MSTR);

      regmap_write(sai->regmap, FSL_SAI_xMR(tx),
-                  ~0UL - ((1 << min(channels, slots)) - 1));
+                  ~0ULL - ((1ULL << min(channels, slots)) - 1));

      return 0;
  }