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How to set correct clock-frequency in MIPI DSI Display

Question asked by CS Lin on Feb 24, 2020
Latest reply on Feb 24, 2020 by igorpadykov


now we are porting Tianma TM050JDHC02 panel into imx8mq custom board. with vendor provided panel config as below, 

#define LCM_PCLK 82
#define LCM_HACT 720
#define LCM_HFP 92
#define LCM_HBP 80
#define LCM_HSA 20
#define LCM_VACT 1280
#define LCM_VFP 200
#define LCM_VBP 16
#define LCM_VSA 2
#define LCM_NLANE 4
#define LCM_VDOMODE 0
#define LCM_MIPISPEED 500

Our question is, if we set LCM_PCLK to 82Mhz or 120Mhz to "clock-frequency" in DTS (please refer to DTS.txt), then panel will show nothing, and you will have a of of 

[ 1.474487] [drm] Cannot find any crtc or sizes
[ 1.479995] [drm] Initialized imx-drm 1.0.0 20120507 for display-subsystem on minor 0

you can refer the log of log inilog_82Mhz.log for full logs.

But if we set it to 132MHz, we it can show the display content, but if will have a log of

dcss-core 32e00000.dcss: Pixel clock set to 120000 kHz instead of 132000 kHz, difference is -12000000 Hz (inilog_132Mhz.log)

Can you help figure out what's wrong with clock-frequency setting in DTS? and what should we modify in DTS to have LCM_PCLK as 82Mhz?

thank you!