Re: [PATCH] drm/meson: vclk: fix calculation of 59.94 fractional rates

[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index]

 



Hi,

On 10/01/2024 00:07, Christian Hewitt wrote:
Playing 4K media with 59.94 fractional rate (typically VP9) causes the screen to lose
sync with the following error reported in the system log:

[   89.610280] Fatal Error, invalid HDMI vclk freq 593406

Modetest shows the following:

3840x2160 59.94 3840 4016 4104 4400 2160 2168 2178 2250 593407 flags: xxxx, xxxx,
drm calculated value -------------------------------------^

Change the fractional rate calculation to stop DIV_ROUND_CLOSEST rounding down which
results in vclk freq failing to match correctly.

Thanks for the patch, it may need to closely look what's would be the consequence
here, since /1000)*1000 would reduce comparison to less digits, but why ?

A good thing would be to find the offending commit of when this broke, or redo
the entire math because it looks super fishy a few years later...

What puzzles me is that the same calculation is done on both side:
- meson_vclk_vic_supported_freq() called from meson_encoder_hdmi_mode_valid()
- meson_vclk_setup() called from meson_encoder_hdmi_set_vclk() and meson_encoder_hdmi_atomic_enable()

so when a mode freq is selected from meson_encoder_hdmi_mode_valid(), it should match the
mode freq in meson_vclk_setup(), but no.
So why reducing precision makes this work ???

Neil


Fixes: e5fab2ec9ca4 ("drm/meson: vclk: add support for YUV420 setup")
Signed-off-by: Christian Hewitt <christianshewitt@xxxxxxxxx>
---
I'm unable to give a better mathematical description of the fix as I can barely read
code. The change was inspired by [0] which I chanced upon while looking at how other
dw-hdmi drivers handle fractional rates.

[0] https://github.com/torvalds/linux/commit/4f510aa10468954b1da4e94689c38ac6ea8d3627

  drivers/gpu/drm/meson/meson_vclk.c | 6 +++---
  1 file changed, 3 insertions(+), 3 deletions(-)

diff --git a/drivers/gpu/drm/meson/meson_vclk.c b/drivers/gpu/drm/meson/meson_vclk.c
index 2a82119eb58e..2a942dc6a6dc 100644
--- a/drivers/gpu/drm/meson/meson_vclk.c
+++ b/drivers/gpu/drm/meson/meson_vclk.c
@@ -790,13 +790,13 @@ meson_vclk_vic_supported_freq(struct meson_drm *priv, unsigned int phy_freq,
  				 FREQ_1000_1001(params[i].pixel_freq));
  		DRM_DEBUG_DRIVER("i = %d phy_freq = %d alt = %d\n",
  				 i, params[i].phy_freq,
-				 FREQ_1000_1001(params[i].phy_freq/10)*10);
+				 FREQ_1000_1001(params[i].phy_freq/1000)*1000);
  		/* Match strict frequency */
  		if (phy_freq == params[i].phy_freq &&
  		    vclk_freq == params[i].vclk_freq)
  			return MODE_OK;
  		/* Match 1000/1001 variant */
-		if (phy_freq == (FREQ_1000_1001(params[i].phy_freq/10)*10) &&
+		if (phy_freq == (FREQ_1000_1001(params[i].phy_freq/1000)*1000) &&
  		    vclk_freq == FREQ_1000_1001(params[i].vclk_freq))
  			return MODE_OK;
  	}
@@ -1070,7 +1070,7 @@ void meson_vclk_setup(struct meson_drm *priv, unsigned int target,
for (freq = 0 ; params[freq].pixel_freq ; ++freq) {
  		if ((phy_freq == params[freq].phy_freq ||
-		     phy_freq == FREQ_1000_1001(params[freq].phy_freq/10)*10) &&
+		     phy_freq == FREQ_1000_1001(params[freq].phy_freq/1000)*1000) &&
  		    (vclk_freq == params[freq].vclk_freq ||
  		     vclk_freq == FREQ_1000_1001(params[freq].vclk_freq))) {
  			if (vclk_freq != params[freq].vclk_freq)




[Index of Archives]     [Linux DRI Users]     [Linux Intel Graphics]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Yosemite News]     [Linux Kernel]     [Linux SCSI]     [XFree86]     [Linux USB Devel]     [Video for Linux]     [Linux Audio Users]     [Linux Kernel]     [Linux SCSI]     [XFree86]
  Powered by Linux