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

[Imre Deak]

On Fri, Mar 29, 2024 at 11:39:39AM -0700, Manasi Navare wrote:
> Hi Imre,
> 
> While we are adding these checks here for DSC for MST, I see that in
> intel_dp_mst_mode_valid_ctx() we still check against DISPLAY_VER() >
> 10 for checking for DSC where as in all other places we rely on
> runtime has_dsc and check for HAS_DSC(), can we fix that and use
> HAS_DSC() in this function as well as part of this series that in
> general fixes some DSC issues?

The check in intel_dp_mst_check_constraints() this patch changes is not
about whether a platform supports DSC or not, rather if the platform has
a DSC/DPT interface limit that needs to be checked. The caller has
already determined that DSC is supported by the platform and it's needed
for the given mode being computed (dsc==true).

> 
> Manasi
> 
> On Tue, Mar 26, 2024 at 5:59 AM Nautiyal, Ankit K
> <ankit.k.nautiyal at intel.com> wrote:
> >
> >
> > On 3/26/2024 5:41 PM, Imre Deak wrote:
> > > 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.
> >
> > Makes sense.
> >
> > >
> > >> 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+.
> >
> > Agreed. Bspec indeed mentions the same thing, and its mentioned
> > appropriately in the next patch.
> >
> > Regards,
> >
> > Ankit
> >
> > >
> > >> 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,