Re: [PATCH 2/2] drm/i915/dsi: Use a fuzzy check for burst mode clock check

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Hi,

Thank you for the reviews.

On 04-06-19 19:29, Ville Syrjälä wrote:
On Fri, May 24, 2019 at 07:40:28PM +0200, Hans de Goede wrote:
Prior to this commit we fail to init the DSI panel on the GPD MicroPC:
https://www.indiegogo.com/projects/gpd-micropc-6-inch-handheld-industry-laptop#/

The problem is intel_dsi_vbt_init() failing with the following error:
*ERROR* Burst mode freq is less than computed

The pclk in the VBT panel modeline is 70000, together with 24 bpp and
4 lines this results in a bitrate value of 70000 * 24 / 4 = 420000.
But the target_burst_mode_freq in the VBT is 418000.

This commit works around this problem by adding an intel_fuzzy_clock_check
when target_burst_mode_freq < bitrate and setting target_burst_mode_freq to
bitrate when that checks succeeds, fixing the panel not working.

Cc: stable@xxxxxxxxxxxxxxx
Signed-off-by: Hans de Goede <hdegoede@xxxxxxxxxx>
---
  drivers/gpu/drm/i915/intel_dsi_vbt.c | 11 +++++++++++
  1 file changed, 11 insertions(+)

diff --git a/drivers/gpu/drm/i915/intel_dsi_vbt.c b/drivers/gpu/drm/i915/intel_dsi_vbt.c
index 022bf59418df..a2a9b9d0eeaa 100644
--- a/drivers/gpu/drm/i915/intel_dsi_vbt.c
+++ b/drivers/gpu/drm/i915/intel_dsi_vbt.c
@@ -895,6 +895,17 @@ bool intel_dsi_vbt_init(struct intel_dsi *intel_dsi, u16 panel_id)
  		if (mipi_config->target_burst_mode_freq) {
  			u32 bitrate = intel_dsi_bitrate(intel_dsi);
+ /*
+			 * Sometimes the VBT contains a slightly lower clock,
+			 * then the bitrate we have calculated, in this case
+			 * just replace it with the calculated bitrate.
+			 */
+			if (mipi_config->target_burst_mode_freq < bitrate &&
+			    intel_fuzzy_clock_check(
+					mipi_config->target_burst_mode_freq,
+					bitrate))
+				mipi_config->target_burst_mode_freq = bitrate;

Maybe should squash these patches together to make the stable
backport less painful?

Good idea, done.

Anyways, seems OK to me.
Reviewed-by: Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx>

And pushed with your Reviewed-by.

Regards,

Hans
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