[PATCH] drm/omap: fix max fclk divider for omap36xx

Tomi Valkeinen tomi.valkeinen at ti.com
Wed Oct 2 12:25:42 UTC 2019

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

Signed-off-by: Tomi Valkeinen <tomi.valkeinen at ti.com>
Cc: Adam Ford <aford173 at gmail.com>
Cc: stable at vger.kernel.org
 drivers/gpu/drm/omapdrm/dss/dss.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/omapdrm/dss/dss.c b/drivers/gpu/drm/omapdrm/dss/dss.c
index e226324adb69..4bdd63b57100 100644
--- a/drivers/gpu/drm/omapdrm/dss/dss.c
+++ b/drivers/gpu/drm/omapdrm/dss/dss.c
@@ -1083,7 +1083,7 @@ static const struct dss_features omap34xx_dss_feats = {
 static const struct dss_features omap3630_dss_feats = {
 	.model			=	DSS_MODEL_OMAP3,
-	.fck_div_max		=	32,
+	.fck_div_max		=	31,
 	.fck_freq_max		=	173000000,
 	.dss_fck_multiplier	=	1,
 	.parent_clk_name	=	"dpll4_ck",
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