linux-kernel - [PATCH 3.16 013/136] drm/omap: fix max fclk divider for omap36xx

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Date:   Tue, 17 Dec 2019 00:45:47 +0000
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, Denis Kirjanov <kda@...ux-powerpc.org>,
        "Jyri Sarha" <jsarha@...com>,
        "Tomi Valkeinen" <tomi.valkeinen@...com>,
        "Adam Ford" <aford173@...il.com>
Subject: [PATCH 3.16 013/136] drm/omap: fix max fclk divider for omap36xx

3.16.80-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Tomi Valkeinen <tomi.valkeinen@...com>

commit e2c4ed148cf3ec8669a1d90dc66966028e5fad70 upstream.

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: Tomi Valkeinen <tomi.valkeinen@...com>
Cc: Adam Ford <aford173@...il.com>
Link: https://patchwork.freedesktop.org/patch/msgid/20191002122542.8449-1-tomi.valkeinen@ti.com
Tested-by: Adam Ford <aford173@...il.com>
Reviewed-by: Jyri Sarha <jsarha@...com>
[bwh: Backported to 3.16: adjust filename, context]
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/video/fbdev/omap2/dss/dss.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

--- a/drivers/video/fbdev/omap2/dss/dss.c
+++ b/drivers/video/fbdev/omap2/dss/dss.c
@@ -708,7 +708,7 @@ static const struct dss_features omap34x
 };
 
 static const struct dss_features omap3630_dss_feats __initconst = {
-	.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,