On Tue, Feb 11, 2025 at 09:06:19PM +0300, Danila Tikhonov wrote:
> On 2/9/25 01:09, Marijn Suijten wrote:
> > On 2025-02-03 21:14:26, Danila Tikhonov wrote:
> > > From: Eugene Lepshy <fekz115@xxxxxxxxx>
> > >
> > > DRM DSC helper has parameters for various bpc values other than 8:
> > Weird zero-width \u200b spaces here between "values" and "other", please delete
> > those.
> Thanks, I will fix it in the next version.
> > > (8/10/12/14/16).
> > >
> > > Remove this guard.
> > >
> > > Signed-off-by: Eugene Lepshy <fekz115@xxxxxxxxx>
> > > Signed-off-by: Danila Tikhonov <danila@xxxxxxxxxxx>
> > Should this patch elaborate that those "DRM DSC helper" don't have any
> > additional guarding for the values you mention either, i.e. passing 9 or 11 or
> > > 16 don't seem to be checked anywhere else either?
> There are no other bpc checks, you are right. But to be honest I don't
> really see any sense in this. Anyway, if you still want us to leave the
> current guard and just extend it with new values (for example via
> switch case) - let me know.
Yes, please. Add a caselist and also a note that only 8, 10 and 12 are
valid for DSC 1.1 block. Then whoever stomps upon other bpc value will
have to extend the check, verifying DSC version.
> > And your title might have space to spell out "Bits Per Component" entirely.
> I'll fix that too.
> > > ---
> > > drivers/gpu/drm/msm/dsi/dsi_host.c | 7 +------
> > > 1 file changed, 1 insertion(+), 6 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/msm/dsi/dsi_host.c b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > > index 007311c21fda..d182af7bbb81 100644
> > > --- a/drivers/gpu/drm/msm/dsi/dsi_host.c
> > > +++ b/drivers/gpu/drm/msm/dsi/dsi_host.c
> > > @@ -1767,11 +1767,6 @@ static int dsi_populate_dsc_params(struct msm_dsi_host *msm_host, struct drm_dsc
> > > return -EINVAL;
> > > }
> > > - if (dsc->bits_per_component != 8) {
> > > - DRM_DEV_ERROR(&msm_host->pdev->dev, "DSI does not support bits_per_component != 8 yet\n");
> > > - return -EOPNOTSUPP;
> > > - }
> > > -
> > > dsc->simple_422 = 0;
> > > dsc->convert_rgb = 1;
> > > dsc->vbr_enable = 0;
> > This seems supicous on the dpu1 side, in the original DSC 1.1 (not 1.2) block in
> > dpu_hw_dsc_config(), which has:
> >
> > data |= (dsc->line_buf_depth << 3);
> > data |= (dsc->simple_422 << 2);
> > data |= (dsc->convert_rgb << 1);
> > data |= dsc->bits_per_component;
> >
> > The original value of `8` would overlap with the lowest bit of line_buf_depth
> > (4th bit in `data`). Now, the 2nd bit which will take the value from
> > convert_rgb, which is already set to 1 above, will overlap with the 2nd bit in
> > your new bpc value of 10.
> >
> > Can you double-check that this code in DPU1 is actually valid? I assume you
> > have tested this panel at least and it is working (worthy mention in the cover
> > letter?), this just seems like yet another mistake in the original bindings
> > (though the register always had a matching value with downstream on 8 BPC panels
> > for me).
>
> Of course I have tested the panel and it works, I just thought it would
> be obvious. We also have tested sm7150-xiaomi-courbet, sm8450-xiaomi-cupid
> and sm8475-nothing-pong, which already have bpp = bpc = 10 panels and
> with some hack it also work without any changes to the DRM.
This is now being fixed by a separate patch.
>
> > > @@ -1779,7 +1774,7 @@ static int dsi_populate_dsc_params(struct msm_dsi_host *msm_host, struct drm_dsc
> > > drm_dsc_set_const_params(dsc);
> > > drm_dsc_set_rc_buf_thresh(dsc);
> > > - /* handle only bpp = bpc = 8, pre-SCR panels */
> > > + /* handle only pre-SCR panels */
> > > ret = drm_dsc_setup_rc_params(dsc, DRM_DSC_1_1_PRE_SCR);
> > Good catch - this comment sounds like it's documenting a limitation of
> > this helper function, but the function does not have such limitations...
> > rc_parameters_pre_scr has values for all these combinations.
> Maybe we should remove this comment entirely?
No, the pre-SCR comment is fine.
>
> Regards,
> Danila
> > - Marijn
> >
> > > if (ret) {
> > > DRM_DEV_ERROR(&msm_host->pdev->dev, "could not find DSC RC parameters\n");
> > > --
> > > 2.48.1
> > >
--
With best wishes
Dmitry
