Re: [Intel-gfx] [PATCH v2 1/8] drm/i915: Add _PICK_EVEN_2RANGES()

[Lucas De Marchi <lucas.demarchi@intel.com>]

On Fri, Jan 20, 2023 at 10:14:19PM -0800, Anusha Srivatsa wrote:
>
>
>> -----Original Message-----
>> From: Intel-gfx <intel-gfx-bounces@lists.freedesktop.org> On Behalf Of Lucas
>> De Marchi
>> Sent: Friday, January 20, 2023 11:35 AM
>> To: intel-gfx@lists.freedesktop.org
>> Cc: De Marchi, Lucas <lucas.demarchi@intel.com>; dri-
>> devel@lists.freedesktop.org
>> Subject: [Intel-gfx] [PATCH v2 1/8] drm/i915: Add _PICK_EVEN_2RANGES()
>>
>> It's a constant pattern in the driver to need to use 2 ranges of MMIOs based on
>> port, phy, pll, etc. When that happens, instead of using _PICK_EVEN(), _PICK()
>> needs to be used.  Using _PICK() is discouraged due to some reasons like:
>>
>> 1) It increases the code size since the array is declared
>>    in each call site
>> 2) Developers need to be careful not to incur an
>>    out-of-bounds array access
>> 3) Developers need to be careful that the indexes match the
>>    table. For that it may be that the table needs to contain
>>    holes, making (1) even worse.
>>
>> Add a variant of _PICK_EVEN() that works with 2 ranges and selects which one
>> to use depending on the index value.
>>
>> Signed-off-by: Lucas De Marchi <lucas.demarchi@intel.com>
>> ---
>>  drivers/gpu/drm/i915/i915_reg_defs.h | 28 ++++++++++++++++++++++++++++
>>  1 file changed, 28 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/i915_reg_defs.h
>> b/drivers/gpu/drm/i915/i915_reg_defs.h
>> index be43580a6979..b7ec87464d69 100644
>> --- a/drivers/gpu/drm/i915/i915_reg_defs.h
>> +++ b/drivers/gpu/drm/i915/i915_reg_defs.h
>> @@ -119,6 +119,34 @@
>>   */
>>  #define _PICK_EVEN(__index, __a, __b) ((__a) + (__index) * ((__b) - (__a)))
>>
>> +/*
>> + * Like _PICK_EVEN(), but supports 2 ranges of evenly spaced address offsets.
>> + * The first range is used for indexes below @__c_index, and the second
>> + * range is used for anything above it. Example::
>> + *
>> + * #define _FOO_A			0xf000
>> + * #define _FOO_B			0xf004
>> + * #define _FOO_C			0xf008
>> + * #define _SUPER_FOO_A			0xa000
>> + * #define _SUPER_FOO_B			0xa100
>> + * #define FOO(x)			_MMIO(_PICK_EVEN_RANGES(x, 3,
>> 		\
>> + *					      _FOO_A, _FOO_B,
>> 	\
>> + *					      _SUPER_FOO_A, _SUPER_FOO_B))
>> + *
>> + * This expands to:
>> + *	0: 0xf000,
>> + *	1: 0xf004,
>> + *	2: 0xf008,
>> + *	3: 0xa100,
>You mean 3:0xa000

doesn't really matter. This is an example of register addresses. They
don't need to start from 0, it's whatever the hw gives us.

Lucas De Marchi

>
>> + *	4: 0xa200,
>4:0xa100
>
>> + *	5: 0xa300,
>5:0xa200
>
>Anusha
>> + *	...
>> + */
>> +#define _PICK_EVEN_2RANGES(__index, __c_index, __a, __b, __c, __d)
>> 	\
>> +	(BUILD_BUG_ON_ZERO(!__is_constexpr(__c_index)) +
>> 	\
>> +	 ((__index) < (__c_index) ? _PICK_EVEN(__index, __a, __b) :
>> 	\
>> +				   _PICK_EVEN((__index) - (__c_index), __c,
>> __d)))
>> +
>>  /*
>>   * Given the arbitrary numbers in varargs, pick the 0-based __index'th number.
>>   *
>> --
>> 2.39.0
>