linux-kernel - Re: [PATCH] fbdev/omap: fix max fclk divider for omap36xx

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Date:   Mon, 21 Oct 2019 11:44:21 +0300
From:   Tomi Valkeinen <tomi.valkeinen@...com>
To:     Adam Ford <aford173@...il.com>, <linux-fbdev@...r.kernel.org>
CC:     <linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <adam.ford@...icpd.com>, <stable@...r.kernel.org>
Subject: Re: [PATCH] fbdev/omap: fix max fclk divider for omap36xx

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@...il.com>
> Cc: Tomi Valkeinen <tomi.valkeinen@...com>
> Cc: stable@...r.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@...com>

  Tomi

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