On Thu, 27 Sep 2018, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
> Quoting Jani Nikula (2018-09-27 10:40:23)
>> Slightly verbose, but does away with hand rolled shifts and provides
>> static checking that the values fit the mask.
>>
>> Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
>> ---
>> @@ -4650,11 +4650,11 @@ enum {
>> #define _PP_ON_DELAYS 0x61208
>> #define PP_ON_DELAYS(pps_idx) _MMIO_PPS(pps_idx, _PP_ON_DELAYS)
>> #define PANEL_PORT_SELECT_MASK GENMASK(31, 30)
>> -#define PANEL_PORT_SELECT_LVDS (0 << 30)
>> -#define PANEL_PORT_SELECT_DPA (1 << 30)
>> -#define PANEL_PORT_SELECT_DPC (2 << 30)
>> -#define PANEL_PORT_SELECT_DPD (3 << 30)
>> -#define PANEL_PORT_SELECT_VLV(port) ((port) << 30)
>> +#define PANEL_PORT_SELECT_LVDS FIELD_PREP(PANEL_PORT_SELECT_MASK, 0)
>> +#define PANEL_PORT_SELECT_DPA FIELD_PREP(PANEL_PORT_SELECT_MASK, 1)
>> +#define PANEL_PORT_SELECT_DPC FIELD_PREP(PANEL_PORT_SELECT_MASK, 2)
>> +#define PANEL_PORT_SELECT_DPD FIELD_PREP(PANEL_PORT_SELECT_MASK, 3)
>> +#define PANEL_PORT_SELECT_VLV(port) FIELD_PREP(PANEL_PORT_SELECT_MASK, port)
>
> Maybe verbose, but it reads far better as giving each field a distinct
> name ties together all the individual options.
>
> Before seeing this I was sceptical about FIELD_PREP, no longer.
>
> Under this construct we aren't using masks per se, but giving a name to
> a group of bits within the register (a field). So I think
>
> #define PANEL_PORT_SELECT GENMASK(31, 30)
> #define PANEL_PORT_SELECT_LVDS FIELD_PREP(PANEL_PORT_SELECT, 0)
Argh, I've screwed up. I must have failed to build after adding the last
patch. You know, RFC and all. This results in:
drivers/gpu/drm/i915/intel_display.c: In function ‘assert_panel_unlocked’:
drivers/gpu/drm/i915/intel_display.c:1219:3: error: case label does not reduce to an integer constant
case PANEL_PORT_SELECT_LVDS:
Fail.
However, taking just the mask&shift part from FIELD_PREP works:
(((typeof(_mask))(_val) << __bf_shf(_mask)) & (_mask))
But then we'll lose the static checks, unless we come up with something
ingenious ourselves.
BR,
Jani.
>
> is intuitive. Did you do a quick bloatometer to see if gcc code
> generation is affected?
> -Chris
--
Jani Nikula, Intel Open Source Graphics Center
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