linux-kernel - Re: [PATCH 12/23] drm: omapdrm: plane: update fifo size on atomic update

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Date:   Wed, 14 Dec 2016 15:03:08 +0100
From:   Sebastian Reichel <sre@...nel.org>
To:     Tomi Valkeinen <tomi.valkeinen@...com>
Cc:     Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        dri-devel@...ts.freedesktop.org, Tony Lindgren <tony@...mide.com>,
        Aaro Koskinen <aaro.koskinen@....fi>,
        linux-omap@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 12/23] drm: omapdrm: plane: update fifo size on atomic
 update

Hi,

On Wed, Dec 14, 2016 at 11:14:32AM +0200, Tomi Valkeinen wrote:
> On 14/12/16 11:10, Laurent Pinchart wrote:
> > Hi Tomi,
> > 
> > On Wednesday 14 Dec 2016 10:43:18 Tomi Valkeinen wrote:
> >> On 13/12/16 19:35, Laurent Pinchart wrote:
> >>> On Tuesday 08 Mar 2016 17:39:44 Sebastian Reichel wrote:
> >>>> This is a workaround for a hardware bug occuring
> >>>> on OMAP3 with manually updated panels.
> >>>
> >>> Could you please explain what the bug is and how the workaround operates ?
> >>> Do you have a reference to an errata document ?

FWIW I don't know anything about this bug. I just hit it while
getting omapdrm working on n950 and ported this over from omapfb.

> >> I don't think I ever found out exactly why the problem happens. But on
> >> OMAP3 DSI, the fifo thresholds had to be tuned slightly, otherwise DISPC
> >> would stop. dispc_ovl_compute_fifo_thresholds() does that tuning if
> >> "manual_update" parameter is set on OMAP3.
> > 
> > I've had a look at dispc_ovl_compute_fifo_thresholds() and the patch makes 
> > sense to me. If Sebastian could address the small issues I pointed out, we 
> > could then merge this. Alternatively I can take care of addressing them.
> 
> It's only needed with the rest of the DSI manual update series, so I'd
> rather keep it as part of that series.

To be honest I haven't worked on this for some time. From some
comments on the patchset I think the biggest issue is, that omapdrm
does not use generic panel drivers and cannot easily use the
mipi_dsi_driver_register. I simply did not have enough time to
implement such a huge change.

I guess a first step is Peter Ujfalusi's series:
https://lkml.org/lkml/2016/9/1/267

-- Sebastian

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