linux-kernel - Re: [Freedreno] [PATCH 03/11] drm/msm/dpu: use hsync/vsync polarity set by the encoder

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Message-ID: <CAA8EJppALF2wZ6QPsHUDWsThHyKMELfwmJbh3neEnN8AHkzDwQ@mail.gmail.com>
Date:   Thu, 20 Apr 2023 21:36:43 +0300
From:   Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To:     Jeykumar Sankaran <quic_jeykumar@...cinc.com>
Cc:     Arnaud Vrac <avrac@...ebox.fr>, Rob Clark <robdclark@...il.com>,
        Abhinav Kumar <quic_abhinavk@...cinc.com>,
        Sean Paul <sean@...rly.run>, David Airlie <airlied@...il.com>,
        Daniel Vetter <daniel@...ll.ch>, linux-arm-msm@...r.kernel.org,
        freedreno@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org
Subject: Re: [Freedreno] [PATCH 03/11] drm/msm/dpu: use hsync/vsync polarity
 set by the encoder

On Thu, 20 Apr 2023 at 21:01, Jeykumar Sankaran
<quic_jeykumar@...cinc.com> wrote:
>
>
>
> On 4/19/2023 7:41 AM, Arnaud Vrac wrote:
> > Do not override the hsync/vsync polarity passed by the encoder when
> > setting up intf timings. The same logic was used in both the encoder and
> > intf code to set the DP and DSI polarities, so those interfaces are not
> > impacted. However for HDMI, the polarities were overriden to static
> > values based on the vertical resolution, instead of using the actual
> > mode polarities.
> >
> Any idea why vres based static polarity override was in place? Hope you
> had tested HDMI resolutions with yres > and < than 720.

I think it migrated from the old fbdev, see [1].
Tthis easily causes issues with the DVI monitors, which have different
rules for hsync/vsync. I have observed this on other platforms.
In practice it was observed that EDID provides correct sync polarity,
so it is better to follow the EDID data. If for some reason EDID is
incorrect, DRM provides a way to override it.

[1] https://git.codelinaro.org/clo/la/kernel/msm-3.18/-/commit/29c3d616bf3f89f13bbab46c58151ae7a3a79b98

>
> Jeykumar S.
>
> > Signed-off-by: Arnaud Vrac <avrac@...ebox.fr>
> > ---
> >   drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c | 16 +++-------------
> >   1 file changed, 3 insertions(+), 13 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c
> > index 84ee2efa9c664..9f05417eb1213 100644
> > --- a/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c
> > +++ b/drivers/gpu/drm/msm/disp/dpu1/dpu_hw_intf.c
> > @@ -104,7 +104,7 @@ static void dpu_hw_intf_setup_timing_engine(struct dpu_hw_intf *ctx,
> >       u32 active_h_start, active_h_end;
> >       u32 active_v_start, active_v_end;
> >       u32 active_hctl, display_hctl, hsync_ctl;
> > -     u32 polarity_ctl, den_polarity, hsync_polarity, vsync_polarity;
> > +     u32 polarity_ctl, den_polarity;
> >       u32 panel_format;
> >       u32 intf_cfg, intf_cfg2 = 0;
> >       u32 display_data_hctl = 0, active_data_hctl = 0;
> > @@ -191,19 +191,9 @@ static void dpu_hw_intf_setup_timing_engine(struct dpu_hw_intf *ctx,
> >       }
> >
> >       den_polarity = 0;
> > -     if (ctx->cap->type == INTF_HDMI) {
> > -             hsync_polarity = p->yres >= 720 ? 0 : 1;
> > -             vsync_polarity = p->yres >= 720 ? 0 : 1;
> > -     } else if (ctx->cap->type == INTF_DP) {
> > -             hsync_polarity = p->hsync_polarity;
> > -             vsync_polarity = p->vsync_polarity;
> > -     } else {
> > -             hsync_polarity = 0;
> > -             vsync_polarity = 0;
> > -     }
> >       polarity_ctl = (den_polarity << 2) | /*  DEN Polarity  */
> > -             (vsync_polarity << 1) | /* VSYNC Polarity */
> > -             (hsync_polarity << 0);  /* HSYNC Polarity */
> > +             (p->vsync_polarity << 1) | /* VSYNC Polarity */
> > +             (p->hsync_polarity << 0);  /* HSYNC Polarity */
> >
> >       if (!DPU_FORMAT_IS_YUV(fmt))
> >               panel_format = (fmt->bits[C0_G_Y] |
> >



-- 
With best wishes
Dmitry