Re: [PATCH 1/4] OMAPDSS: Fix DSS clock multiplier issue on 3703 and probably 3630

Tomi Valkeinen
2014-05-09T07:38:54Z

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On 30/04/14 02:52, Tony Lindgren wrote:
> Otherwise we can get often errors like the following and the
> display won't come on:
>
> omapdss APPLY error: FIFO UNDERFLOW on gfx, disabling the overlay
> omapdss APPLY error: SYNC_LOST on channel lcd, restarting
> the output with video overlays disabled
>
> There are some earlier references to this issue:
>
> http://www.spinics.net/lists/linux-omap/msg59511.html
> http://www.spinics.net/lists/linux-omap/msg59724.html

Those don't sound like the same issue, but it's hard to say. What kind
of clock rates do you get? Cat you paste debugfs/omapdss/clk, with and
without this patch?

What resolution do you have? If it's a very high resolution (say, DVI
output to a monitor), it could just be an issue of
not-enough-memory-bandwidth.

> It seems that it's safe to set the lower values even for 3630.
> If we can confirm that 3630 works with the higher values
> reliably we can add further detection.
>
> Signed-off-by: Tony Lindgren <tony@atomide.com>
> ---
> drivers/video/fbdev/omap2/dss/dss.c | 5 +++--
> 1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/video/fbdev/omap2/dss/dss.c b/drivers/video/fbdev/omap2/dss/dss.c
> index d55266c..ad6561f 100644
> --- a/drivers/video/fbdev/omap2/dss/dss.c
> +++ b/drivers/video/fbdev/omap2/dss/dss.c
> @@ -707,9 +707,10 @@ static const struct dss_features omap34xx_dss_feats __initconst = {
> .dpi_select_source = &dss_dpi_select_source_omap2_omap3,
> };
>
> +/* Supposedly 3630 can use div 32 mult 2, but that needs to be rechecked */
> static const struct dss_features omap3630_dss_feats __initconst = {
> - .fck_div_max = 32,
> - .dss_fck_multiplier = 1,
> + .fck_div_max = 16,
> + .dss_fck_multiplier = 2,

These values tell about the clock hardware, they are not settings that
can be changed to change the clock. OMAP3630 has a fixed x2 multiplier
and a divider with maximum value of 16.

Tomi

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