fbdev/omap: fix max fclk divider for omap36xx
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Message ID 20191018124938.29313-1-aford173@gmail.com
State New
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Series
  • fbdev/omap: fix max fclk divider for omap36xx
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Commit Message

Adam Ford Oct. 18, 2019, 12:49 p.m. UTC
The OMAP36xx and AM/DM37x TRMs say that the maximum divider for DSS fclk
(in CM_CLKSEL_DSS) is 32. Experimentation shows that this is not
correct, and using divider of 32 breaks DSS with a flood or underflows
and sync losts. Dividers up to 31 seem to work fine.

There is another patch to the DT files to limit the divider correctly,
but as the DSS driver also needs to know the maximum divider to be able
to iteratively find good rates, we also need to do the fix in the DSS
driver.

Signed-off-by: Adam Ford <aford173@gmail.com>
Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
Cc: stable@vger.kernel.org #linux-4.9.y+

Comments

Tomi Valkeinen Oct. 21, 2019, 8:42 a.m. UTC | #1
On 18/10/2019 15:49, Adam Ford wrote:
> The OMAP36xx and AM/DM37x TRMs say that the maximum divider for DSS fclk
> (in CM_CLKSEL_DSS) is 32. Experimentation shows that this is not
> correct, and using divider of 32 breaks DSS with a flood or underflows
> and sync losts. Dividers up to 31 seem to work fine.
> 
> There is another patch to the DT files to limit the divider correctly,
> but as the DSS driver also needs to know the maximum divider to be able
> to iteratively find good rates, we also need to do the fix in the DSS
> driver.
> 
> Signed-off-by: Adam Ford <aford173@gmail.com>
> Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
> Cc: stable@vger.kernel.org #linux-4.9.y+
> 
> diff --git a/drivers/video/fbdev/omap2/omapfb/dss/dss.c b/drivers/video/fbdev/omap2/omapfb/dss/dss.c
> index 48c6500c24e1..4429ad37b64c 100644
> --- a/drivers/video/fbdev/omap2/omapfb/dss/dss.c
> +++ b/drivers/video/fbdev/omap2/omapfb/dss/dss.c
> @@ -843,7 +843,7 @@ static const struct dss_features omap34xx_dss_feats = {
>   };
>   
>   static const struct dss_features omap3630_dss_feats = {
> -	.fck_div_max		=	32,
> +	.fck_div_max		=	31,
>   	.dss_fck_multiplier	=	1,
>   	.parent_clk_name	=	"dpll4_ck",
>   	.dpi_select_source	=	&dss_dpi_select_source_omap2_omap3,
> 

Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

  Tomi
Adam Ford Nov. 8, 2019, 1:09 p.m. UTC | #2
On Mon, Oct 21, 2019 at 3:42 AM Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:
>
> On 18/10/2019 15:49, Adam Ford wrote:
> > The OMAP36xx and AM/DM37x TRMs say that the maximum divider for DSS fclk
> > (in CM_CLKSEL_DSS) is 32. Experimentation shows that this is not
> > correct, and using divider of 32 breaks DSS with a flood or underflows
> > and sync losts. Dividers up to 31 seem to work fine.
> >
> > There is another patch to the DT files to limit the divider correctly,
> > but as the DSS driver also needs to know the maximum divider to be able
> > to iteratively find good rates, we also need to do the fix in the DSS
> > driver.
> >
> > Signed-off-by: Adam Ford <aford173@gmail.com>
> > Cc: Tomi Valkeinen <tomi.valkeinen@ti.com>
> > Cc: stable@vger.kernel.org #linux-4.9.y+
> >
> > diff --git a/drivers/video/fbdev/omap2/omapfb/dss/dss.c b/drivers/video/fbdev/omap2/omapfb/dss/dss.c
> > index 48c6500c24e1..4429ad37b64c 100644
> > --- a/drivers/video/fbdev/omap2/omapfb/dss/dss.c
> > +++ b/drivers/video/fbdev/omap2/omapfb/dss/dss.c
> > @@ -843,7 +843,7 @@ static const struct dss_features omap34xx_dss_feats = {
> >   };
> >
> >   static const struct dss_features omap3630_dss_feats = {
> > -     .fck_div_max            =       32,
> > +     .fck_div_max            =       31,
> >       .dss_fck_multiplier     =       1,
> >       .parent_clk_name        =       "dpll4_ck",
> >       .dpi_select_source      =       &dss_dpi_select_source_omap2_omap3,
> >
>
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>

What is the next step to get these integrated into 4.9+?

adam
>
>   Tomi
>
> --
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki

Patch
diff mbox series

diff --git a/drivers/video/fbdev/omap2/omapfb/dss/dss.c b/drivers/video/fbdev/omap2/omapfb/dss/dss.c
index 48c6500c24e1..4429ad37b64c 100644
--- a/drivers/video/fbdev/omap2/omapfb/dss/dss.c
+++ b/drivers/video/fbdev/omap2/omapfb/dss/dss.c
@@ -843,7 +843,7 @@  static const struct dss_features omap34xx_dss_feats = {
 };
 
 static const struct dss_features omap3630_dss_feats = {
-	.fck_div_max		=	32,
+	.fck_div_max		=	31,
 	.dss_fck_multiplier	=	1,
 	.parent_clk_name	=	"dpll4_ck",
 	.dpi_select_source	=	&dss_dpi_select_source_omap2_omap3,