[PATCH 3/3] drm/i915: Temporary conversion to new GENMASK/BIT macros

[Lucas De Marchi]

On Tue, May 09, 2023 at 10:57:19AM +0300, Jani Nikula wrote:
>On Mon, 08 May 2023, Lucas De Marchi <lucas.demarchi at intel.com> wrote:
>> Convert the REG_* macros from i915_reg_defs.h to use the new macros
>> defined in linux/bits.h. This is just to help on the implementation
>> of the new macros and not intended to be applied.
>
>This drops a number of build time input checks as well as casts to the
>specified types.

the explicit checks... but the checks are still there and the compiler
still gives me a warning or error for using invalid values. See test program in
the second patch. Example:

	static const u32 a2 = GENMASK_U32(32, 0);

	In file included from /tmp/genmask.c:2:                                                                                                                             
	include/linux/bits.h:47:19: warning: right shift count is negative [-Wshift-count-negative]                                                                         
	   47 |          (~U32(0) >> (32 - 1 - (h))))                                                                                                                       
	      |                   ^~                                                                                                                                        

It's a warning, not an error though.

Same warning for the other fixed-widths with numbers above the supported width.
For negative values:

	In file included from include/linux/bits.h:21,                                     
			 from /tmp/genmask.c:2:                                            
	include/linux/build_bug.h:16:51: error: negative width in bit-field ‘<anonymous>’  
	   16 | #define BUILD_BUG_ON_ZERO(e) ((int)(sizeof(struct { int:(-!!(e)); })))     
	      |                                                   ^                        


The cast to the specified type we lose indeed. Could you give an example where
those are useful in the context they are used? I debated adding them, but couldn't find
a justified use of them.

Lucas De Marchi

>
>BR,
>Jani.
>
>>
>> Signed-off-by: Lucas De Marchi <lucas.demarchi at intel.com>
>> ---
>>  drivers/gpu/drm/i915/i915_reg_defs.h | 28 +++++-----------------------
>>  1 file changed, 5 insertions(+), 23 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_reg_defs.h b/drivers/gpu/drm/i915/i915_reg_defs.h
>> index 622d603080f9..61fbb8d62b25 100644
>> --- a/drivers/gpu/drm/i915/i915_reg_defs.h
>> +++ b/drivers/gpu/drm/i915/i915_reg_defs.h
>> @@ -17,10 +17,7 @@
>>   *
>>   * @return: Value with bit @__n set.
>>   */
>> -#define REG_BIT(__n)							\
>> -	((u32)(BIT(__n) +						\
>> -	       BUILD_BUG_ON_ZERO(__is_constexpr(__n) &&		\
>> -				 ((__n) < 0 || (__n) > 31))))
>> +#define REG_BIT(__n) BIT_U32(__n)
>>
>>  /**
>>   * REG_BIT8() - Prepare a u8 bit value
>> @@ -30,10 +27,7 @@
>>   *
>>   * @return: Value with bit @__n set.
>>   */
>> -#define REG_BIT8(__n)                                                   \
>> -	((u8)(BIT(__n) +                                                \
>> -	       BUILD_BUG_ON_ZERO(__is_constexpr(__n) &&         \
>> -				 ((__n) < 0 || (__n) > 7))))
>> +#define REG_BIT8(__n) BIT_U8(__n)
>>
>>  /**
>>   * REG_GENMASK() - Prepare a continuous u32 bitmask
>> @@ -44,11 +38,7 @@
>>   *
>>   * @return: Continuous bitmask from @__high to @__low, inclusive.
>>   */
>> -#define REG_GENMASK(__high, __low)					\
>> -	((u32)(GENMASK(__high, __low) +					\
>> -	       BUILD_BUG_ON_ZERO(__is_constexpr(__high) &&	\
>> -				 __is_constexpr(__low) &&		\
>> -				 ((__low) < 0 || (__high) > 31 || (__low) > (__high)))))
>> +#define REG_GENMASK(__high, __low) GENMASK_U32(__high, __low)
>>
>>  /**
>>   * REG_GENMASK64() - Prepare a continuous u64 bitmask
>> @@ -59,11 +49,7 @@
>>   *
>>   * @return: Continuous bitmask from @__high to @__low, inclusive.
>>   */
>> -#define REG_GENMASK64(__high, __low)					\
>> -	((u64)(GENMASK_ULL(__high, __low) +				\
>> -	       BUILD_BUG_ON_ZERO(__is_constexpr(__high) &&		\
>> -				 __is_constexpr(__low) &&		\
>> -				 ((__low) < 0 || (__high) > 63 || (__low) > (__high)))))
>> +#define REG_GENMASK64(__high, __low) GENMASK_ULL(__high, __low)
>>
>>  /**
>>   * REG_GENMASK8() - Prepare a continuous u8 bitmask
>> @@ -74,11 +60,7 @@
>>   *
>>   * @return: Continuous bitmask from @__high to @__low, inclusive.
>>   */
>> -#define REG_GENMASK8(__high, __low)                                     \
>> -	((u8)(GENMASK(__high, __low) +                                  \
>> -	       BUILD_BUG_ON_ZERO(__is_constexpr(__high) &&      \
>> -				 __is_constexpr(__low) &&               \
>> -				 ((__low) < 0 || (__high) > 7 || (__low) > (__high)))))
>> +#define REG_GENMASK8(__high, __low) GENMASK_U8(__high, __low)
>>
>>  /*
>>   * Local integer constant expression version of is_power_of_2().
>
>-- 
>Jani Nikula, Intel Open Source Graphics Center