-----Original Message-----
From: Tomi Valkeinen <tomi.valkeinen@xxxxxx>
To: Joe Woodward <jw@xxxxxxxxxxxxxx>
Cc: Archit Taneja <a0393947@xxxxxx>, linux-omap@xxxxxxxxxxxxxxx
Date: Thu, 03 May 2012 11:28:41 +0300
Subject: Re: Problems with 3.4-rc5
> On Wed, 2012-05-02 at 13:46 +0100, Joe Woodward wrote:
>
> > > > Secondly, I get the following when booted:
> > > > ...
> > > > [ 4.701232] devtmpfs: mounted
> > > > [ 4.704772] Freeing init memory: 168K
> > > > [ 4.827301] omapdss DISPC error: FIFO UNDERFLOW on gfx,
> disabling
> > > the overlay
> > > > ...
> > > >
> > >
> > > Could you add some dss debug prints? You can add "omapdss.debug=1
> > > debug"
> > > in the bootargs to get that.
> > >
> > > There was a feature called fifo merge added in 3.4, this might lead
> to
> > > underflow, we had tested this using a DVI monitor on beagle but
> didn't
> > > see any underflows.
> > >
> > > Are you trying this out on 3.4 for the first time? What was the
> last
> > > kernel revision on which you tested this and didn't see any issues?
>
> Can you try the following changes (separately):
>
>
> diff --git a/drivers/video/omap2/dss/dispc.c
> b/drivers/video/omap2/dss/dispc.c
> index ee30937..aca4eb1 100644
> --- a/drivers/video/omap2/dss/dispc.c
> +++ b/drivers/video/omap2/dss/dispc.c
> @@ -1091,13 +1091,8 @@ void dispc_ovl_compute_fifo_thresholds(enum
> omap_plane plane,
> * combined fifo size
> */
>
> - if (dss_has_feature(FEAT_OMAP3_DSI_FIFO_BUG)) {
> - *fifo_low = ovl_fifo_size - burst_size * 2;
> - *fifo_high = total_fifo_size - burst_size;
> - } else {
> - *fifo_low = ovl_fifo_size - burst_size;
> - *fifo_high = total_fifo_size - buf_unit;
> - }
> + *fifo_low = ovl_fifo_size - burst_size;
> + *fifo_high = total_fifo_size - buf_unit;
> }
>
> static void dispc_ovl_set_fir(enum omap_plane plane,
>
> ---
The above patch fixes the problem (I no longer see any underflows).
>
> diff --git a/drivers/video/omap2/dss/dispc.c
> b/drivers/video/omap2/dss/dispc.c
> index ee30937..d63f1a3 100644
> --- a/drivers/video/omap2/dss/dispc.c
> +++ b/drivers/video/omap2/dss/dispc.c
> @@ -1077,13 +1077,7 @@ void dispc_ovl_compute_fifo_thresholds(enum
> omap_plane plane,
> burst_size = dispc_ovl_get_burst_size(plane);
> ovl_fifo_size = dispc_ovl_get_fifo_size(plane);
>
> - if (use_fifomerge) {
> - total_fifo_size = 0;
> - for (i = 0; i < omap_dss_get_num_overlays(); ++i)
> - total_fifo_size += dispc_ovl_get_fifo_size(i);
> - } else {
> - total_fifo_size = ovl_fifo_size;
> - }
> + total_fifo_size = ovl_fifo_size;
>
> /*
> * We use the same low threshold for both fifomerge and non-fifomerge
>
The above patch has no effect (I still see underflows).
Both patches together results in slightly different behaviour, the display is still broken-
it flickers on and off with occassional underflows before breaking completely.
Cheers,
Joe
> Tomi
>
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