Re: [Intel-gfx] [PATCH 1/2] drm/i915/reg: fix undefined behavior due to shift overflowing the constant

[Jani Nikula <jani.nikula@intel.com>]

On Wed, 18 May 2022, Ville Syrjälä <ville.syrjala@linux.intel.com> wrote:
> On Wed, May 18, 2022 at 02:33:14PM +0300, Jani Nikula wrote:
>> Use REG_GENMASK() and REG_FIELD_PREP() to avoid errors due to
>> -fsanitize=shift.
>
> I presume it's just unhappy about shifting into the sign bit?

Yeah, and apparently it also only happens on some GCC versions. *shrug*.

>
> Changes look correct:
> Reviewed-by: Ville Syrjälä <ville.syrjala@linux.intel.com>

Thanks,
Jani.

>
>> 
>> References: https://lore.kernel.org/r/20220405151517.29753-12-bp@alien8.de
>> Reported-by: Borislav Petkov <bp@suse.de>
>> Reported-by: Ruiqi GONG <gongruiqi1@huawei.com>
>> Cc: Randy Dunlap <rdunlap@infradead.org>
>> Signed-off-by: Jani Nikula <jani.nikula@intel.com>
>> ---
>>  drivers/gpu/drm/i915/i915_reg.h | 32 ++++++++++++++++----------------
>>  1 file changed, 16 insertions(+), 16 deletions(-)
>> 
>> diff --git a/drivers/gpu/drm/i915/i915_reg.h b/drivers/gpu/drm/i915/i915_reg.h
>> index 321a08281a3f..dff3f88d8090 100644
>> --- a/drivers/gpu/drm/i915/i915_reg.h
>> +++ b/drivers/gpu/drm/i915/i915_reg.h
>> @@ -7607,25 +7607,25 @@ enum skl_power_gate {
>>  #define _PORT_CLK_SEL_A			0x46100
>>  #define _PORT_CLK_SEL_B			0x46104
>>  #define PORT_CLK_SEL(port) _MMIO_PORT(port, _PORT_CLK_SEL_A, _PORT_CLK_SEL_B)
>> -#define  PORT_CLK_SEL_LCPLL_2700	(0 << 29)
>> -#define  PORT_CLK_SEL_LCPLL_1350	(1 << 29)
>> -#define  PORT_CLK_SEL_LCPLL_810		(2 << 29)
>> -#define  PORT_CLK_SEL_SPLL		(3 << 29)
>> -#define  PORT_CLK_SEL_WRPLL(pll)	(((pll) + 4) << 29)
>> -#define  PORT_CLK_SEL_WRPLL1		(4 << 29)
>> -#define  PORT_CLK_SEL_WRPLL2		(5 << 29)
>> -#define  PORT_CLK_SEL_NONE		(7 << 29)
>> -#define  PORT_CLK_SEL_MASK		(7 << 29)
>> +#define  PORT_CLK_SEL_MASK		REG_GENMASK(31, 29)
>> +#define  PORT_CLK_SEL_LCPLL_2700	REG_FIELD_PREP(PORT_CLK_SEL_MASK, 0)
>> +#define  PORT_CLK_SEL_LCPLL_1350	REG_FIELD_PREP(PORT_CLK_SEL_MASK, 1)
>> +#define  PORT_CLK_SEL_LCPLL_810		REG_FIELD_PREP(PORT_CLK_SEL_MASK, 2)
>> +#define  PORT_CLK_SEL_SPLL		REG_FIELD_PREP(PORT_CLK_SEL_MASK, 3)
>> +#define  PORT_CLK_SEL_WRPLL(pll)	REG_FIELD_PREP(PORT_CLK_SEL_MASK, 4 + (pll))
>> +#define  PORT_CLK_SEL_WRPLL1		REG_FIELD_PREP(PORT_CLK_SEL_MASK, 4)
>> +#define  PORT_CLK_SEL_WRPLL2		REG_FIELD_PREP(PORT_CLK_SEL_MASK, 5)
>> +#define  PORT_CLK_SEL_NONE		REG_FIELD_PREP(PORT_CLK_SEL_MASK, 7)
>>  
>>  /* On ICL+ this is the same as PORT_CLK_SEL, but all bits change. */
>>  #define DDI_CLK_SEL(port)		PORT_CLK_SEL(port)
>> -#define  DDI_CLK_SEL_NONE		(0x0 << 28)
>> -#define  DDI_CLK_SEL_MG			(0x8 << 28)
>> -#define  DDI_CLK_SEL_TBT_162		(0xC << 28)
>> -#define  DDI_CLK_SEL_TBT_270		(0xD << 28)
>> -#define  DDI_CLK_SEL_TBT_540		(0xE << 28)
>> -#define  DDI_CLK_SEL_TBT_810		(0xF << 28)
>> -#define  DDI_CLK_SEL_MASK		(0xF << 28)
>> +#define  DDI_CLK_SEL_MASK		REG_GENMASK(31, 28)
>> +#define  DDI_CLK_SEL_NONE		REG_FIELD_PREP(DDI_CLK_SEL_MASK, 0x0)
>> +#define  DDI_CLK_SEL_MG			REG_FIELD_PREP(DDI_CLK_SEL_MASK, 0x8)
>> +#define  DDI_CLK_SEL_TBT_162		REG_FIELD_PREP(DDI_CLK_SEL_MASK, 0xC)
>> +#define  DDI_CLK_SEL_TBT_270		REG_FIELD_PREP(DDI_CLK_SEL_MASK, 0xD)
>> +#define  DDI_CLK_SEL_TBT_540		REG_FIELD_PREP(DDI_CLK_SEL_MASK, 0xE)
>> +#define  DDI_CLK_SEL_TBT_810		REG_FIELD_PREP(DDI_CLK_SEL_MASK, 0xF)
>>  
>>  /* Transcoder clock selection */
>>  #define _TRANS_CLK_SEL_A		0x46140
>> -- 
>> 2.30.2

-- 
Jani Nikula, Intel Open Source Graphics Center