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

[Hans de Goede]

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 at vger.kernel.org
>> Signed-off-by: Hans de Goede <hdegoede at redhat.com>
>> ---
>>   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 at linux.intel.com>

And pushed with your Reviewed-by.

Regards,

Hans