Re: [PATCH V6 6/6] drm: bridge: samsung-dsim: Support non-burst mode

[Adam Ford]

On Mon, May 15, 2023 at 10:26 PM Chen-Yu Tsai <wenst@xxxxxxxxxxxx> wrote:
>
> On Tue, May 16, 2023 at 7:57 AM Adam Ford <aford173@xxxxxxxxx> wrote:
> >
> > The high-speed clock is hard-coded to the burst-clock
> > frequency specified in the device tree.  However, when
> > using devices like certain bridge chips without burst mode
> > and varying resolutions and refresh rates, it may be
> > necessary to set the high-speed clock dynamically based
> > on the desired pixel clock for the connected device.
> >
> > This also removes the need to set a clock speed from
> > the device tree for non-burst mode operation, since the
> > pixel clock rate is the rate requested from the attached
> > device like a bridge chip.  This should have no impact
> > for people using burst-mode and setting the burst clock
> > rate is still required for those users.  If the burst
> > clock is not present, change the error message to
> > dev_info indicating the clock use the pixel clock.
> >
> > Signed-off-by: Adam Ford <aford173@xxxxxxxxx>
> > Tested-by: Chen-Yu Tsai <wenst@xxxxxxxxxxxx>
> > Tested-by: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx>
> > Reviewed-by: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx>
> > ---
> >  drivers/gpu/drm/bridge/samsung-dsim.c | 27 +++++++++++++++++++++------
> >  1 file changed, 21 insertions(+), 6 deletions(-)
> >
> > diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> > index 3944b7cfbbdf..03b21d13f067 100644
> > --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> > +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> > @@ -655,16 +655,28 @@ static unsigned long samsung_dsim_set_pll(struct samsung_dsim *dsi,
> >
> >         dsi->hs_clock = fout;
> >
> > +       dsi->hs_clock = fout;
> > +
>
> Not sure about the double assignment. Was this caused by a rebase?

Oops,

I moved this to the previous patch since the updated dphy changes
needed to know the hs_clock. I must forgot to check this when I
applied the subsequent patch, so the double assignment appeared.  I am
surprised the patch tool didn't complain.  I guess the good news is
that nothing is broken, but the bad news is I have to spam everyone
with a V7.  I'll wait a couple days to see if anything finds anything
else.

adam
>
> ChenYu
>
> >         return fout;
> >  }
> >
> >  static int samsung_dsim_enable_clock(struct samsung_dsim *dsi)
> >  {
> > -       unsigned long hs_clk, byte_clk, esc_clk;
> > +       unsigned long hs_clk, byte_clk, esc_clk, pix_clk;
> >         unsigned long esc_div;
> >         u32 reg;
> > +       struct drm_display_mode *m = &dsi->mode;
> > +       int bpp = mipi_dsi_pixel_format_to_bpp(dsi->format);
> > +
> > +       /* m->clock is in KHz */
> > +       pix_clk = m->clock * 1000;
> > +
> > +       /* Use burst_clk_rate if available, otherwise use the pix_clk */
> > +       if (dsi->burst_clk_rate)
> > +               hs_clk = samsung_dsim_set_pll(dsi, dsi->burst_clk_rate);
> > +       else
> > +               hs_clk = samsung_dsim_set_pll(dsi, DIV_ROUND_UP(pix_clk * bpp, dsi->lanes));
> >
> > -       hs_clk = samsung_dsim_set_pll(dsi, dsi->burst_clk_rate);
> >         if (!hs_clk) {
> >                 dev_err(dsi->dev, "failed to configure DSI PLL\n");
> >                 return -EFAULT;
> > @@ -935,7 +947,7 @@ static void samsung_dsim_set_display_mode(struct samsung_dsim *dsi)
> >         u32 reg;
> >
> >         if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO) {
> > -               int byte_clk_khz = dsi->burst_clk_rate / 1000 / 8;
> > +               int byte_clk_khz = dsi->hs_clock / 1000 / 8;
> >                 int hfp = (m->hsync_start - m->hdisplay) * byte_clk_khz / m->clock;
> >                 int hbp = (m->htotal - m->hsync_end) * byte_clk_khz / m->clock;
> >                 int hsa = (m->hsync_end - m->hsync_start) * byte_clk_khz / m->clock;
> > @@ -1785,10 +1797,13 @@ static int samsung_dsim_parse_dt(struct samsung_dsim *dsi)
> >                         return PTR_ERR(pll_clk);
> >         }
> >
> > +       /* If it doesn't exist, use pixel clock instead of failing */
> >         ret = samsung_dsim_of_read_u32(node, "samsung,burst-clock-frequency",
> > -                                      &dsi->burst_clk_rate, 0);
> > -       if (ret < 0)
> > -               return ret;
> > +                                      &dsi->burst_clk_rate, 1);
> > +       if (ret < 0) {
> > +               dev_info(dev, "Using pixel clock for HS clock frequency\n");
> > +               dsi->burst_clk_rate = 0;
> > +       }
> >
> >         ret = samsung_dsim_of_read_u32(node, "samsung,esc-clock-frequency",
> >                                        &dsi->esc_clk_rate, 0);
> > --
> > 2.39.2
> >