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

From: [email-masked] (Tomi Valkeinen)
Date: Fri, 9 May 2014 10:38:54 +0300

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 <[email-masked]>
> ---
>  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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