AM335x invert LCD clock for fbdev in device tree kernel 3.12

erwel

Other Parts Discussed in Thread: DA8XX

For getting my LCD display to function correctly I'm trying to invert the LCD clock on Linux kernel 3.12 with device tree on the da8xx fbdev, but I can't seem to find the correct option for it. In the da8xx-fb.c driver I have found:

if (panel->sync & FB_SYNC_CLK_INVERT)
		lcdc_write((lcdc_read(LCD_RASTER_TIMING_2_REG) |
			LCD_INVERT_PIXEL_CLOCK), LCD_RASTER_TIMING_2_REG);
	else
		lcdc_write((lcdc_read(LCD_RASTER_TIMING_2_REG) &
			~LCD_INVERT_PIXEL_CLOCK), LCD_RASTER_TIMING_2_REG);

FB_SYNC_CLK_INVERT is defined in da8xx-fb.h as 0x40000000

I tested with the 3.2 kernel by using ".invert_pxl_clk = 1" in the lcd_panels and this worked perfectly, now with 3.12 I can't find the option in the device tree.

Can somebody provide me a push in the right direction please?

over 11 years ago

0 Miroslav Kiradzhiyski XID over 11 years ago

TI__Mastermind 25235 points

Hi Erwel,

Try adding the following to the device tree inside the panel-info structure:

invert-pxl-clk;

Best regards,
Miroslav

invert-pxl-clk;

0 erwel over 11 years ago in reply to Miroslav Kiradzhiyski XID

Intellectual 280 points

Miroslav,

Thank you for the response, adding invert-pxl-clk; to the panel-info works perfectly. But this requires the DRM driver to be used instead of the by default enabled fbdev driver. Is there a way to invert the pixel clock in the fbdev driver?

I'm assuming the fbdev driver is enabled by default because the DRM driver isn't production ready yet?

0 erwel over 11 years ago in reply to erwel

Intellectual 280 points

I just read in http://processors.wiki.ti.com/index.php/Linux_Core_LCD_Controller_User_Guide that there are no downfalls for me to use DRM. I'm marking this question as answered but for future references would still like to know if it is possible with the fbdev driver.

0 Josh Elliott over 11 years ago in reply to erwel

TI__Expert 3010 points

Hello,

The primary reason we use fbdev as the default driver is due to the Graphics SDK's dependence on fbdev. The Graphics SDK provides the drivers for the 3D hardware on AM335x. Otherwise, we would use DRM as the default driver. You can find more information here: http://processors.wiki.ti.com/index.php/Sitara_SDK_Linux_LCDC

Regards,

Josh

0 erwel over 11 years ago in reply to Josh Elliott

Intellectual 280 points

Josh,

Thank you for the clarification. I need to have the 3D acceleration drivers so I guess I'm stuck with fbdev. Is it possible to invert the pixel clock using the fbdev driver in device tree?

0 Josh Elliott over 11 years ago in reply to erwel

TI__Expert 3010 points

Hello,

I haven't tested it personally, but the pixelclk-active field in the display timings might work for you.

http://lxr.free-electrons.com/source/Documentation/devicetree/bindings/video/display-timing.txt

Regards,

Josh

0 erwel over 11 years ago in reply to Josh Elliott

Intellectual 280 points

Josh,

That seems correct , I want to sample data on falling clock instead of rising. But the pixelclk-active field doesn't seem to do anything when set to either <0> or <1>

In the driver I can find

if (panel->sync & FB_SYNC_CLK_INVERT)
		lcdc_write((lcdc_read(LCD_RASTER_TIMING_2_REG) |
			LCD_INVERT_PIXEL_CLOCK), LCD_RASTER_TIMING_2_REG);
	else
		lcdc_write((lcdc_read(LCD_RASTER_TIMING_2_REG) &
			~LCD_INVERT_PIXEL_CLOCK), LCD_RASTER_TIMING_2_REG);

Where FB_SYNC_CLK_INVERT is defined in the header file and never seems to be set in the struct fb_videomode->sync

Processors

Processors forum

AM335x invert LCD clock for fbdev in device tree kernel 3.12