[PATCH 05/11] drm/i915/dp_mst: Account with the DSC DPT bpp limit on MTL

[Imre Deak]

On Tue, Mar 26, 2024 at 03:47:05PM +0530, Nautiyal, Ankit K wrote:
> 
> On 3/21/2024 1:41 AM, Imre Deak wrote:
> > The DPT/DSC bpp limit should be accounted for on MTL platforms as well,
> > do so.
> > 
> > Bspec: 49259
> > 
> > Signed-off-by: Imre Deak <imre.deak at intel.com>
> > ---
> >   drivers/gpu/drm/i915/display/intel_dp_mst.c | 2 +-
> >   1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/gpu/drm/i915/display/intel_dp_mst.c b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > index 79f34be5c89da..40660dc5edb45 100644
> > --- a/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > +++ b/drivers/gpu/drm/i915/display/intel_dp_mst.c
> > @@ -56,7 +56,7 @@ static int intel_dp_mst_check_constraints(struct drm_i915_private *i915, int bpp
> >   					  struct intel_crtc_state *crtc_state,
> >   					  bool dsc)
> >   {
> > -	if (intel_dp_is_uhbr(crtc_state) && DISPLAY_VER(i915) < 14 && dsc) {
> 
> Should this be DISPLAY_VER() <= 14 to include MTL?

The actual change is the DISPLAY_VER() < 20 below, which is the usual
way in the driver (AFAIU) to check for an upper bound.

> For DISPLAY_VER 20, is there another check?
> 
> in Bspec:68912 it mentions output bpp * pixel clock < DDICLK * 144 bits

Yes LNL is different, but there this DPT limit should never be a
bottleneck. Ville has an idea to abstract this more, but this patchset
keeps things as-is, skipping the check on LNL+.

> Regards,
> 
> Ankit
> 
> > +	if (intel_dp_is_uhbr(crtc_state) && DISPLAY_VER(i915) < 20 && dsc) {
> >   		int output_bpp = bpp;
> >   		int symbol_clock = intel_dp_link_symbol_clock(crtc_state->port_clock);
> >   		int available_bw = mul_u32_u32(symbol_clock * 72,