[PATCH v3 0/3] drm/sun4i: hdmi: Fix sun4i_tmds_determine_rate

[PATCH v3 0/3] drm/sun4i: hdmi: Fix sun4i_tmds_determine_rate

[Jonathan Liu]

This patchset fixes several issues in sun4i_tmds_determine_rate that I
discovered while trying to get a projector connected to an Olimex
A20-OLinuXino-LIME using HDMI with a native resolution of 1280x800 and
pixel clock of 83.5 MHz to display at its native resolution.

Changes for v3:
- Improve commit message for unset best_parent

Changes for v2:
- Split into separate patches for each issue
- Add details to commit message for reproducing issue

Jonathan Liu (3):
  drm/sun4i: hdmi: Check for unset best_parent in
    sun4i_tmds_determine_rate
  drm/sun4i: hdmi: Fix incorrect assignment in sun4i_tmds_determine_rate
  drm/sun4i: hdmi: Add missing rate halving check in
    sun4i_tmds_determine_rate

 drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c | 9 ++++++---
 1 file changed, 6 insertions(+), 3 deletions(-)

-- 
2.15.1

[PATCH v3 1/3] drm/sun4i: hdmi: Check for unset best_parent in sun4i_tmds_determine_rate

[Jonathan Liu]

It is possible that if there is no exact rate match and
"rounded = clk_hw_round_rate(parent, ideal)" gives high enough values
(e.g. if rounded is 2 * ideal) that the condition
"abs(rate - rounded / i) < abs(rate - best_parent / best_div)" is never
met and best_parent is never set. This results in req->rate and
req->best_parent_rate being assigned 0.

To avoid this, we set best_parent to the first calculated rate if it is
unset. The sun4i_tmds_calc_divider function already has a similar check.

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

diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c
index dc332ea56f6c..4d235e5ea31c 100644
--- a/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c
+++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c
@@ -102,7 +102,7 @@ static int sun4i_tmds_determine_rate(struct clk_hw *hw,
 					goto out;
 				}
 
-				if (abs(rate - rounded / i) <
+				if (!best_parent || abs(rate - rounded / i) <
 				    abs(rate - best_parent / best_div)) {
 					best_parent = rounded;
 					best_div = i;
-- 
2.15.1

[PATCH v3 2/3] drm/sun4i: hdmi: Fix incorrect assignment in sun4i_tmds_determine_rate

[Jonathan Liu]

best_div is set to i which corresponds to rate halving when it should be
set to j which corresponds to the divider.

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

diff --git a/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c b/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c
index 4d235e5ea31c..88eeeaf34638 100644
--- a/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c
+++ b/drivers/gpu/drm/sun4i/sun4i_hdmi_tmds_clk.c
@@ -105,7 +105,7 @@ static int sun4i_tmds_determine_rate(struct clk_hw *hw,
 				if (!best_parent || abs(rate - rounded / i) <
 				    abs(rate - best_parent / best_div)) {
 					best_parent = rounded;
-					best_div = i;
+					best_div = j;
 				}
 			}
 		}
-- 
2.15.1

[PATCH v3 3/3] drm/sun4i: hdmi: Add missing rate halving check in sun4i_tmds_determine_rate

[Jonathan Liu]

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@gmail.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

[PATCH v3 0/3] drm/sun4i: hdmi: Fix sun4i_tmds_determine_rate

[Maxime Ripard]

On Tue, Jan 09, 2018 at 01:03:20PM +1100, Jonathan Liu wrote:
> This patchset fixes several issues in sun4i_tmds_determine_rate that I
> discovered while trying to get a projector connected to an Olimex
> A20-OLinuXino-LIME using HDMI with a native resolution of 1280x800 and
> pixel clock of 83.5 MHz to display at its native resolution.

Queued all three patches as fixes, thanks!
maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com
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