Re: [Intel-gfx] [PATCH v3 2/8] drm/i915: update the QGV point frequency calculations

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

On Fri, 28 Apr 2023, "Govindapillai, Vinod" <vinod.govindapillai@intel.com> wrote:
> On Thu, 2023-04-27 at 18:04 +0300, Ville Syrjälä wrote:
>> On Thu, Apr 27, 2023 at 06:00:10PM +0300, Vinod Govindapillai wrote:
>> > > From MTL onwwards, pcode locks the QGV point based on peak BW of
>> > the intended QGV point passed by the driver. So the peak BW
>> > calculation must match the value expected by the pcode. Update
>> > the calculations as per the Bspec.
>> > 
>> > Bspec: 64636
>> > 
>> > Signed-off-by: Vinod Govindapillai <vinod.govindapillai@intel.com>
>> > ---
>> >  drivers/gpu/drm/i915/display/intel_bw.c | 2 +-
>> >  1 file changed, 1 insertion(+), 1 deletion(-)
>> > 
>> > diff --git a/drivers/gpu/drm/i915/display/intel_bw.c b/drivers/gpu/drm/i915/display/intel_bw.c
>> > index ab405c48ca3a..25ae4e5834d3 100644
>> > --- a/drivers/gpu/drm/i915/display/intel_bw.c
>> > +++ b/drivers/gpu/drm/i915/display/intel_bw.c
>> > @@ -182,7 +182,7 @@ static int mtl_read_qgv_point_info(struct drm_i915_private *dev_priv,
>> >         val2 = intel_uncore_read(&dev_priv->uncore,
>> >                                  MTL_MEM_SS_INFO_QGV_POINT_HIGH(point));
>> >         dclk = REG_FIELD_GET(MTL_DCLK_MASK, val);
>> > -       sp->dclk = DIV_ROUND_UP((16667 * dclk), 1000);
>> > +       sp->dclk = (16667 * dclk + 500) / 1000;
>> 
>> Don't hand roll rounding.
>
> Hi Ville,
>
> I did not understand what you meant by this.
>
> This is as per the Bspec 64636. I am assuming, probably this is what pcode expects to get it
> compared with its internal reference qclk peak Bw. I will clarify with Art.
>
> And there is another requirement to get rid of div_round_up() of these BW calculations. Will address
> them separately.

The point is, no matter whether you need to round up or down or nearest,
you need to use the DIV_ROUND_* helpers for that, not duplicate the
logic here. No matter what bspec says.

BR,
Jani.


>
> BR
> Vinod
>> 
>> >         sp->t_rp = REG_FIELD_GET(MTL_TRP_MASK, val);
>> >         sp->t_rcd = REG_FIELD_GET(MTL_TRCD_MASK, val);
>> >  
>> > -- 
>> > 2.34.1
>> 
>

-- 
Jani Nikula, Intel Open Source Graphics Center