fbdev/omap: fix max fclk divider for omap36xx
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Message ID 20191018130507.29893-1-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, 1:05 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-4.4.y only

Comments

Tomi Valkeinen Oct. 21, 2019, 8:44 a.m. UTC | #1
On 18/10/2019 16:05, 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-4.4.y only
> 
> diff --git a/drivers/video/fbdev/omap2/dss/dss.c b/drivers/video/fbdev/omap2/dss/dss.c
> index 9200a8668b49..a57c3a5f4bf8 100644
> --- a/drivers/video/fbdev/omap2/dss/dss.c
> +++ b/drivers/video/fbdev/omap2/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,
> 

To clarify, this patch is only for the v4.4 stable, whereas the previous 
patch was for next merge window and v4.9+ stable. Right?

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

  Tomi
Adam Ford Oct. 21, 2019, 11:07 a.m. UTC | #2
On Mon, Oct 21, 2019 at 3:44 AM Tomi Valkeinen <tomi.valkeinen@ti.com> wrote:
>
> On 18/10/2019 16:05, 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-4.4.y only
> >
> > diff --git a/drivers/video/fbdev/omap2/dss/dss.c b/drivers/video/fbdev/omap2/dss/dss.c
> > index 9200a8668b49..a57c3a5f4bf8 100644
> > --- a/drivers/video/fbdev/omap2/dss/dss.c
> > +++ b/drivers/video/fbdev/omap2/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,
> >
>
> To clarify, this patch is only for the v4.4 stable, whereas the previous
> patch was for next merge window and v4.9+ stable. Right?

That is correct.  The patch I did for 4.9+ didn't apply cleanly on
4.4, so I had to do a separate patch for 4.4.

adam
>
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ti.com>
>
>   Tomi
>
> --
> Texas Instruments Finland Oy, Porkkalankatu 22, 00180 Helsinki.
> Y-tunnus/Business ID: 0615521-4. Kotipaikka/Domicile: Helsinki
Adam Ford Nov. 8, 2019, 1:10 p.m. UTC | #3
On Fri, Oct 18, 2019 at 8:05 AM Adam Ford <aford173@gmail.com> 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-4.4.y only

This is basically the same patch as the only Tomi reviewed for 4.9,
but it is based on 4.4.

Is there any way these can be integrated?

thank you,

adam
>
> diff --git a/drivers/video/fbdev/omap2/dss/dss.c b/drivers/video/fbdev/omap2/dss/dss.c
> index 9200a8668b49..a57c3a5f4bf8 100644
> --- a/drivers/video/fbdev/omap2/dss/dss.c
> +++ b/drivers/video/fbdev/omap2/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,
> --
> 2.17.1
>

Patch
diff mbox series

diff --git a/drivers/video/fbdev/omap2/dss/dss.c b/drivers/video/fbdev/omap2/dss/dss.c
index 9200a8668b49..a57c3a5f4bf8 100644
--- a/drivers/video/fbdev/omap2/dss/dss.c
+++ b/drivers/video/fbdev/omap2/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,