As per BSPEC, valid cdclk values for glk are 79.2, 158.4, 316.8 Mhz.
Practically we can achive only 99% of these cdclk values (HW team
checking on this). So cdclk should be calculated for the given pixclk as
per that otherwise it may lead to screen corruption, explained below:
1. For DSI AUO panel(1920x1200 @60) required pixclk is 157100 KHZ
2. glk_calc_cdclk returns 79200 KHZ for this pixclk, For 2PPC it
will be 158400 KHZ
3. Practically 100% of the cdclk can’t be achieved, so 99% of 158400
KHZ = 156816 which is less than the desired pixlclk and causes
panel corruption.
v2: Rebased to new CDLCK code framework
v3: Addressed review comments from Ander/Jani
- Add comment in code about 99% usage of CDCLK
- Calculate max dot clock as well with 99% limit
v4 by Jani:
- drop superfluous whitespace change
- rewrite code comments to clarify
v5: Added details of non-working scenario in commit message
Cc: Ander Conselvan de Oliveira <ander.conselvan.de.oliveira@xxxxxxxxx>
Cc: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>
Signed-off-by: Madhav Chauhan <madhav.chauhan@xxxxxxxxx>
Signed-off-by: Jani Nikula <jani.nikula@xxxxxxxxx>
Reviewed-by: Ander Conselvan de Oliveira <conselvan2@xxxxxxxxx>
---
drivers/gpu/drm/i915/intel_cdclk.c | 16 +++++++++++++---
1 file changed, 13 insertions(+), 3 deletions(-)
diff --git a/drivers/gpu/drm/i915/intel_cdclk.c b/drivers/gpu/drm/i915/intel_cdclk.c
index dd3ad52..763010f 100644
--- a/drivers/gpu/drm/i915/intel_cdclk.c
+++ b/drivers/gpu/drm/i915/intel_cdclk.c
@@ -1071,9 +1071,15 @@ static int bxt_calc_cdclk(int max_pixclk)
static int glk_calc_cdclk(int max_pixclk)
{
- if (max_pixclk > 2 * 158400)
+ /*
+ * FIXME: Avoid using a pixel clock that is more than 99% of the cdclk
+ * as a temporary workaround. Use a higher cdclk instead. (Note that
+ * intel_compute_max_dotclk() limits the max pixel clock to 99% of max
+ * cdclk.)
+ */
+ if (max_pixclk > DIV_ROUND_UP(2 * 158400 * 99, 100))
return 316800;
- else if (max_pixclk > 2 * 79200)
+ else if (max_pixclk > DIV_ROUND_UP(2 * 79200 * 99, 100))
return 158400;
else
return 79200;
@@ -1664,7 +1670,11 @@ static int intel_compute_max_dotclk(struct drm_i915_private *dev_priv)
int max_cdclk_freq = dev_priv->max_cdclk_freq;
if (IS_GEMINILAKE(dev_priv))
- return 2 * max_cdclk_freq;
+ /*
+ * FIXME: Limiting to 99% as a temporary workaround. See
+ * glk_calc_cdclk() for details.
+ */
+ return 2 * max_cdclk_freq * 99 / 100;
else if (INTEL_INFO(dev_priv)->gen >= 9 ||
IS_HASWELL(dev_priv) || IS_BROADWELL(dev_priv))
return max_cdclk_freq;
--
1.9.1
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