On Wed, Aug 27, 2025 at 12:54 PM Timur Kristóf <timur.kris...@gmail.com> wrote:
>
> On Wed, 2025-08-27 at 12:36 -0400, Alex Deucher wrote:
> > On Wed, Aug 27, 2025 at 10:36 AM Timur Kristóf
> > <timur.kris...@gmail.com> wrote:
> > >
> > > On Tue, 2025-08-26 at 10:03 -0400, Alex Deucher wrote:
> > > > On Mon, Aug 25, 2025 at 6:10 PM Timur Kristóf
> > > > <timur.kris...@gmail.com> wrote:
> > > > >
> > > > > Change the legacy (non-DC) display code to respect the maximum
> > > > > pixel clock for HDMI and DVI-D. Reject modes that would require
> > > > > a higher pixel clock than can be supported.
> > > > >
> > > > > Also update the maximum supported HDMI clock value depending on
> > > > > the ASIC type.
> > > > >
> > > > > For reference, see the DC code:
> > > > > check max_hdmi_pixel_clock in dce*_resource.c
> > > > >
> > > > > Signed-off-by: Timur Kristóf <timur.kris...@gmail.com>
> > > > > ---
> > > > > .../gpu/drm/amd/amdgpu/amdgpu_connectors.c | 21
> > > > > +++++++++++++++++--
> > > > > 1 file changed, 19 insertions(+), 2 deletions(-)
> > > > >
> > > > > diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> > > > > b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> > > > > index 5e375e9c4f5d..abcc4469cf57 100644
> > > > > --- a/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> > > > > +++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_connectors.c
> > > > > @@ -1195,12 +1195,26 @@ static void
> > > > > amdgpu_connector_dvi_force(struct drm_connector *connector)
> > > > > amdgpu_connector->use_digital = true;
> > > > > }
> > > > >
> > > > > +/**
> > > > > + * Returns the maximum supported HDMI (TMDS) pixel clock in
> > > > > KHz.
> > > > > + */
> > > > > +static int amdgpu_max_hdmi_pixel_clock(const struct
> > > > > amdgpu_device
> > > > > *adev)
> > > > > +{
> > > > > + if (adev->asic_type >= CHIP_POLARIS10)
> > > > > + return 600000;
> > > > > + else if (adev->asic_type >= CHIP_TONGA)
> > > > > + return 300000;
> > > > > + else
> > > > > + return 297000;
> > > > > +}
> > > > > +
> > > > > static enum drm_mode_status
> > > > > amdgpu_connector_dvi_mode_valid(struct
> > > > > drm_connector *connector,
> > > > > const struct
> > > > > drm_display_mode *mode)
> > > > > {
> > > > > struct drm_device *dev = connector->dev;
> > > > > struct amdgpu_device *adev = drm_to_adev(dev);
> > > > > struct amdgpu_connector *amdgpu_connector =
> > > > > to_amdgpu_connector(connector);
> > > > > + const int max_hdmi_pixel_clock =
> > > > > amdgpu_max_hdmi_pixel_clock(adev);
> > > > >
> > > > > /* XXX check mode bandwidth */
> > > > >
> > > > > @@ -1208,10 +1222,13 @@ static enum drm_mode_status
> > > > > amdgpu_connector_dvi_mode_valid(struct drm_connector
> > > > > if ((amdgpu_connector->connector_object_id ==
> > > > > CONNECTOR_OBJECT_ID_DUAL_LINK_DVI_I) ||
> > > > > (amdgpu_connector->connector_object_id ==
> > > > > CONNECTOR_OBJECT_ID_DUAL_LINK_DVI_D) ||
> > > > > (amdgpu_connector->connector_object_id ==
> > > > > CONNECTOR_OBJECT_ID_HDMI_TYPE_B)) {
> > > > > - return MODE_OK;
> > > > > + if (mode->clock > max_hdmi_pixel_clock)
> > > > > + return MODE_CLOCK_HIGH;
> > > > > + else
> > > > > + return MODE_OK;
> > > >
> > > > I don't think it makes sense to limit dual link DVI to the max
> > > > HDMI
> > > > clock. HDMI is single link TMDS. Other than that, the patch
> > > > looks
> > > > good to me.
> > > >
> > > > Alex
> > >
> > > Hi Alex,
> > >
> > > The problem I'm trying to solve here is that on the non-DC code, by
> > > default I get a black screen on DVI-D because the code doesn't set
> > > an
> > > upper limit on what is actually supported. (And the monitor
> > > supports
> > > some modes which won't work.)
> > >
> > > As far as I see, DC only allows 4K 30 Hz on DVI for the same
> > > connector
> > > and DVI/HDMI adapter. That may be wrong, though.
> > >
> > > What value do you suggest to use?
> > >
> > > If HDMI = single link TMDS, does that mean that a passive DVI/HDMI
> > > adapter cannot take advantage of dual-link DVI?
> >
> > DVI has a 165 Mhz limit per link so dual link would be 330 Mhz.
> >
> > Alex
>
> I see. That's my mistake, I thought that the max_hdmi_pixel_clock as
> defined in DC is applicable to all TMDS signals, not just HDMI.
>
> That being said, can you confirm that a DVI/HDMI adapter can indeed use
> both links of the dual-link DVI?
>
DVI to HDMI adapters probably only wire up the a single TMDS link
because that is all HDMI supports. HDMI is single link TMDS and it
was extended beyond 165 Mhz, so most monitors that support HDMI
support faster single link clocks on DVI as well if they have both
inputs since it's the same panel. Older DVI only monitors are
probably the only ones where the single vs dual link clocks are
important.
Alex
> >
> > >
> > > Thanks,
> > > Timur
> > >
> > > >
> > > > > } else if (connector->display_info.is_hdmi) {
> > > > > /* HDMI 1.3+ supports max clock of 340
> > > > > Mhz
> > > > > */
> > > > > - if (mode->clock > 340000)
> > > > > + if (mode->clock > max_hdmi_pixel_clock)
> > > > > return MODE_CLOCK_HIGH;
> > > > > else
> > > > > return MODE_OK;
> > > > > --
> > > > > 2.50.1
> > > > >
