linux-kernel - [PATCH] drm/omap: increase DSS5 max tv pclk to 192MHz

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Message-Id: <20211012133939.2145462-1-narmstrong@baylibre.com>
Date:   Tue, 12 Oct 2021 15:39:39 +0200
From:   Neil Armstrong <narmstrong@...libre.com>
To:     tomba@...nel.org
Cc:     linux-omap@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, khilman@...libre.com,
        Tomi Valkeinen <tomi.valkeinen@...com>,
        Neil Armstrong <narmstrong@...libre.com>
Subject: [PATCH] drm/omap: increase DSS5 max tv pclk to 192MHz

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

DSS5's maximum tv pclk rate (i.e. HDMI) is set to 186MHz, which comes
from the TRM (DPLL_HDMI_CLK1 frequency must be lower than 186 MHz). To
support DRA76's wide screen HDMI feature, we need to increase this
maximum rate.

Testing shows that the PLL seems to work fine even with ~240MHz clocks,
and even the HDMI output at that clock is stable enough for monitors to
show a picture. This holds true for all DRA7 and AM5 SoCs (and probably
also for OMAP5).

However, the highest we can go without big refactoring to the clocking
code is 192MHz, as that is the DSS func clock we get from the PRCM. So,
increase the max HDMI pixel clock to 192MHz for now, to allow some more
2k+ modes to work.

This patch never had a clear confirmation from HW people, but this
change stayed on production trees for multiple years without any report
on an eventual breakage.

Signed-off-by: Tomi Valkeinen <tomi.valkeinen@...com>
Signed-off-by: Neil Armstrong <narmstrong@...libre.com>
---
 drivers/gpu/drm/omapdrm/dss/dispc.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

Tomi,

I slighly changed the commit message to point the fact this patch has been
used in production fort years without any sign of breakage.

Neil

diff --git a/drivers/gpu/drm/omapdrm/dss/dispc.c b/drivers/gpu/drm/omapdrm/dss/dispc.c
index 5619420cc2cc..3c4a4991e45a 100644
--- a/drivers/gpu/drm/omapdrm/dss/dispc.c
+++ b/drivers/gpu/drm/omapdrm/dss/dispc.c
@@ -4458,7 +4458,7 @@ static const struct dispc_features omap54xx_dispc_feats = {
 	.mgr_width_max		=	4096,
 	.mgr_height_max		=	4096,
 	.max_lcd_pclk		=	170000000,
-	.max_tv_pclk		=	186000000,
+	.max_tv_pclk		=	192000000,
 	.max_downscale		=	4,
 	.max_line_width		=	2048,
 	.min_pcd		=	1,

base-commit: e4e737bb5c170df6135a127739a9e6148ee3da82
-- 
2.25.1