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

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Message-ID: <CAHCN7x+DwSSabhGYZ1dnZzwRe+BJfz2H-AXbxjUQWytrq3OMpQ@mail.gmail.com>
Date: Mon, 22 Apr 2024 07:09:13 -0500
From: Adam Ford <aford173@...il.com>
To: Marek Vasut <marex@...x.de>
Cc: dri-devel@...ts.freedesktop.org, aford@...conembedded.com, 
	Frieder Schrempf <frieder.schrempf@...tron.de>, Inki Dae <inki.dae@...sung.com>, 
	Jagan Teki <jagan@...rulasolutions.com>, Marek Szyprowski <m.szyprowski@...sung.com>, 
	Andrzej Hajda <andrzej.hajda@...el.com>, Neil Armstrong <neil.armstrong@...aro.org>, 
	Robert Foss <rfoss@...nel.org>, Laurent Pinchart <Laurent.pinchart@...asonboard.com>, 
	Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>, 
	Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>, Maxime Ripard <mripard@...nel.org>, 
	Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>, Daniel Vetter <daniel@...ll.ch>, 
	Marco Felsch <m.felsch@...gutronix.de>, Michael Tretter <m.tretter@...gutronix.de>, 
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 2/2] drm/bridge: samsung-dsim: Fix porch calcalcuation rounding

On Sun, Apr 21, 2024 at 9:36 AM Marek Vasut <marex@...x.de> 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@...tron.de> # Kontron BL i.MX8MM with HDMI monitor
> > Signed-off-by: Adam Ford <aford173@...il.com>
> > ---
> > 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.

thanks

adam