linux-kernel - [PATCH v3 3/3] drm/sun4i: hdmi: Add missing rate halving check in sun4i_tmds_determine

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Message-Id: <20180109020323.11852-4-net147@gmail.com>
Date:   Tue,  9 Jan 2018 13:03:23 +1100
From:   Jonathan Liu <net147@...il.com>
To:     Maxime Ripard <maxime.ripard@...e-electrons.com>,
        David Airlie <airlied@...ux.ie>, Chen-Yu Tsai <wens@...e.org>
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...glegroups.com,
        Jonathan Liu <net147@...il.com>
Subject: [PATCH v3 3/3] drm/sun4i: hdmi: Add missing rate halving check in sun4i_tmds_determine_rate

It was only checking the divider when determing the closest match if
it could not match the requested rate exactly.

For a projector connected to an Olimex A20-OLinuXino-LIME using HDMI
with a native resolution of 1280x800 and pixel clock of 83.5 MHz, this
resulted in 1280x800 mode not being available and the following in dmesg
when the kernel is booted with drm.debug=0x3e:
[drm:drm_mode_debug_printmodeline] Modeline 37:"1280x800" 60 83500 1280 1352 1480 1680 800 810 816 831 0x48 0x5
[drm:drm_mode_prune_invalid] Not using 1280x800 mode: NOCLOCK

Fixes: 9c5681011a0c ("drm/sun4i: Add HDMI support")
Signed-off-by: Jonathan Liu <net147@...il.com>
---
 drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c
index 88eeeaf34638..3ecffa52c814 100644
--- a/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c
+++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c
@@ -102,9 +102,12 @@ static int sun4i_tmds_determine_rate(struct clk_hw *hw,
 					goto out;
 				}
 
-				if (!best_parent || abs(rate - rounded / i) <
-				    abs(rate - best_parent / best_div)) {
+				if (!best_parent ||
+				    abs(rate - rounded / i / j) <
+				    abs(rate - best_parent / best_half /
+					best_div)) {
 					best_parent = rounded;
+					best_half = i;
 					best_div = j;
 				}
 			}
-- 
2.15.1