Re: [PATCH V2 2/2] drm/bridge: samsung-dsim: Fix porch calcalcuation rounding

[Marek Vasut]

On 4/22/24 3:04 PM, Adam Ford wrote:
> On Mon, Apr 22, 2024 at 8:01 AM Marek Vasut <marex@xxxxxxx> wrote:
> > On 4/22/24 2:09 PM, Adam Ford wrote:
> > > On Sun, Apr 21, 2024 at 9:36 AM Marek Vasut <marex@xxxxxxx> wrote:
> > > > On 2/12/24 12:09 AM, Adam Ford wrote:
> > > > > When using video sync pulses, the HFP, HBP, and HSA are divided between
> > > > > the available lanes if there is more than one lane.  For certain
> > > > > timings and lane configurations, the HFP may not be evenly divisible.
> > > > > If the HFP is rounded down, it ends up being too small which can cause
> > > > > some monitors to not sync properly. In these instances, adjust htotal
> > > > > and hsync to round the HFP up, and recalculate the htotal.
> > > > >
> > > > > Tested-by: Frieder Schrempf <frieder.schrempf@xxxxxxxxxx> # Kontron BL i.MX8MM with HDMI monitor
> > > > > Signed-off-by: Adam Ford <aford173@xxxxxxxxx>
> > > > > ---
> > > > > V2:  No changes
> > > > >
> > > > > diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> > > > > index 8476650c477c..52939211fe93 100644
> > > > > --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> > > > > +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> > > > > @@ -1606,6 +1606,27 @@ static int samsung_dsim_atomic_check(struct drm_bridge *bridge,
> > > > >                 adjusted_mode->flags |= (DRM_MODE_FLAG_PHSYNC | DRM_MODE_FLAG_PVSYNC);
> > > > >         }
> > > > >
> > > > > +     /*
> > > > > +      * When using video sync pulses, the HFP, HBP, and HSA are divided between
> > > > > +      * the available lanes if there is more than one lane.  For certain
> > > > > +      * timings and lane configurations, the HFP may not be evenly divisible.
> > > > > +      * If the HFP is rounded down, it ends up being too small which can cause
> > > > > +      * some monitors to not sync properly. In these instances, adjust htotal
> > > > > +      * and hsync to round the HFP up, and recalculate the htotal. Through trial
> > > > > +      * and error, it appears that the HBP and HSA do not appearto need the same
> > > > > +      * correction that HFP does.
> > > > > +      */
> > > > > +     if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO_SYNC_PULSE && dsi->lanes > 1) {
> > > >
> > > > Does this also apply to mode with sync events (I suspect it does), so
> > > > the condition here should likely be if (!...burst mode) , right ?
> > >
> > > Thanks for the review!
> > >
> > > I was only able to test it with the DSI->ADV6535 bridge, and I'll
> > > admit I don't know a lot about DSI interface since I don't have a copy
> > > of the spec to read.
> > >
> > > Are you proposing this should be:
> > >
> > >    if (!(dsi->mode_flags & MIPI_DSI_MODE_VIDEO_BURST) && dsi->lanes > 1) {
> > >
> > > I just want to make sure I understand what you're requesting.
> >
> > Yes, exactly this.
>
> Do you think it should also include checks for
> MIPI_DSI_MODE_VIDEO_NO_HFP, MIPI_DSI_MODE_VIDEO_NO_HBP or
> MIPI_DSI_MODE_VIDEO_NO_HSA?
>
> It seems like if any of these are set, we should skip this rounding stuff.

Now that you ask this question, shouldn't this actually apply 
unconditionally , no matter which mode is in use ?