Jetson DSI display burst mode

Robotics & Edge Computing Jetson & Embedded Systems Jetson TX2
1

Hi,
someone has experience with writing device tree and driver for DSI Display in burst mode?
i have problems to set the pixel clock, which is calculated from nvidia driver in base of the DTB file.
The driver needs a max_panel_freq_khz for calculation. but i dont know how to set it via DTB.

i tried nvidia,dsi-max_panel_freq_khz = <50000>; but this is not transfered to dsi.c driver.

kernel log

<\n>[    0.455461] tegradc 15200000.nvdisplay: DSI: max_panel_freq_khzis not set for DSI burst mode.<\r>
<\n>[    0.455541] tegradc 15200000.nvdisplay: Force clock continuous mode<\r>

thanks for help.

2

PeterLustig,

I am not sure where did you come from this “nvidia,dsi-max_panel_freq_khz”.

All compatible items are listed in “kernel-4.4/Documentation/devicetree/bindings/video/nvidia,tegra186-dsi.txt”

3

Hi,
it was just a try…
your nvidia driver needs the max_panel_freq_khz value. could you explain how to set it. cause i cant find it in the documents.
thanks

4

PeterLustig,

In fact, I don’t think we have an existing usecase that enables DSI burst mode on L4T. I’ll help check.

Maybe other forum users can share their experience at this moment.

5

PeterLustig,

I just checked the driver code.

if (!dsi->info.max_panel_freq_khz) {
  		dsi->info.max_panel_freq_khz = DEFAULT_MAX_DSI_PHY_CLK_KHZ;
  
  		if (dsi->info.video_burst_mode >
  				TEGRA_DSI_VIDEO_NONE_BURST_MODE_WITH_SYNC_END){
  			dev_err(&dsi->dc->ndev->dev, "DSI: max_panel_freq_khz"
  					"is not set for DSI burst mode.\n");
  			dsi->info.video_burst_mode =
  				TEGRA_DSI_VIDEO_BURST_MODE_LOWEST_SPEED;
  		}
  	}

Even with the error message you met, there is no error return and the max_panel_freq_khz is initialized.

6

PeterLustig,

Please add below parsing code to of_dc.c

diff --git a/drivers/video/tegra/dc/of_dc.c b/drivers/video/tegra/dc/of_dc.c
index e8301e0..2614b07 100644
--- a/drivers/video/tegra/dc/of_dc.c
+++ b/drivers/video/tegra/dc/of_dc.c
@@ -1332,6 +1332,10 @@ static struct device_node *parse_dsi_settings(struct platform_device *ndev,
                }
        }
        if (!of_property_read_u32(np_dsi_panel,
+                       "nvidia,dsi-max-panel-freq-khz", &temp)) {
+               dsi->max_panel_freq_khz= temp;
+       }
+       if (!of_property_read_u32(np_dsi_panel,
                        "nvidia,dsi-pixel-format", &temp)) {
                dsi->pixel_format = (u8)temp;
                if (temp == TEGRA_DSI_PIXEL_FORMAT_16BIT_P)
7

ok thanks,
seems to work.
Still have issues with initialisation of display - but this is different topic.
regards

8

If you manage to enable panel with burst mode, please share the dts here for other user to refer to.

Thanks.

9

PeterLustig,

How is the burst mode? Do you enable it?

10

still using video mode.
dsi display works - burst mode dont work yet.

11

PeterLustig,

Are you still working on the dsi burst mode?

12

Hi,
no not at this moment.
stil using non burst mode.
bye