Enable IMX8MP LVDS panel in uboot

[leavs]

We're currently working on enabling an LVDS display in L5.15.52 for an IMX8MP board. We followed a guide on the NXP community website (https://community.nxp.com/t5/i-MX-Processors-Knowledge-Base/Add-i-MX8MP-LVDS-driver-in-uboot/ta-p/14...), but we're using an LVDS panel instead of an LVDS to HDMI bridge. Consequently, we made some modifications to the U-Boot device tree files and added the panel as a simple panel.

The driver works and print the following in uboot, 

[*]-Video Link 0 (1280 x 800)
[0] lcd-controller@32e90000, video
[1] lvds-channel@0, display
[2] lvds-panel, panel

The questions is that there is no data from the LVDS port, I mean there are 4 data lines and 1 clk line on the LVDS cahnnel 0, the clk has 74M, data 0 and data 1 keep high, data 2 and data 3 has some data(I measured the results using an oscilloscope. I attached one picture to show that).

I can confirm that the hardware is ok as the kernel can display LVDS well.

can you help check what happen?

I use simple-panel as panel driver, and the following dts,

backlight: backlight {
compatible = "pwm-backlight";
pwms = <&pwm1 0 50000>; /* period = 5000000 ns => f = 200 Hz */
brightness-levels = <0 100>;
num-interpolated-steps = <100>;
default-brightness-level = <100>;
status = "okay";
};

lvds_panel: lvds-panel {
compatible = "simple-panel";
backlight = <&backlight>;

display-timings {
native-mode = <&timing0>;

timing0: timing0 {
clock-frequency = <71100000>;
hactive = <1280>;
vactive = <800>;
hback-porch = <40>;
hfront-porch = <40>;
vback-porch = <3>;
vfront-porch = <10>;
hsync-len = <80>;
vsync-len = <10>;
};
};

port {
panel_lvds_in: endpoint {
remote-endpoint = <&lvds_out>;
};
};
};

&lcdif2 {
status = "okay";
};

&ldb_phy {
status = "okay";
};

&ldb {
status = "okay";

lvds-channel@0 {
fsl,data-mapping = "spwg";
fsl,data-width = <24>;
status = "okay";

port@1 {
reg = <1>;

lvds_out: endpoint {
remote-endpoint = <&panel_lvds_in>;
};
};

};
};

[Zhiming_Liu]

Hi @leavs 

Please try below PLL settings.

/* Set Video PLL to 995.4Mhz for LVDS, p = 15, m = 622, k = 8192, s = 0 */

[leavs]

Hi @Zhiming_Liu 

I added the new PLL table, the result is same.

I checked the code detail and find that the clock_init() function in arch/arm/mach-imx/imx8m/clock_imx8mm.c is not run, and the function enable_display_clk() is also not run as I added some debug log in arch/arm/mach-imx/imx8m/clock_imx8mm.c.

I don't know why this clock_init() is not called in this BSP.

What do you think about this?

[Zhiming_Liu · Accepted solution]

Hi @leavs 

This is a demo patch about simple_panel.c, i just set timing in code not dts. You can test it and add code to read timing in device tree.

diff --git a/drivers/video/simple_panel.c b/drivers/video/simple_panel.c
index f9281d5e83..692c96dcaa 100644
--- a/drivers/video/simple_panel.c
+++ b/drivers/video/simple_panel.c
@@ -18,12 +18,27 @@ struct simple_panel_priv {
 	struct gpio_desc enable;
 };
 
+/* define your panel timing here and
+ * copy it in simple_panel_get_display_timing */
+static const struct display_timing boe_ev121wxm_n10_1850_timing = {
+	.pixelclock.typ		= 71143000,
+	.hactive.typ		= 1280,
+	.hfront_porch.typ	= 32,
+	.hback_porch.typ	= 80,
+	.hsync_len.typ		= 48,
+	.vactive.typ		= 800,
+	.vfront_porch.typ	= 6,
+	.vback_porch.typ	= 14,
+	.vsync_len.typ		= 3,
+};
+
@@ -100,10 +121,18 @@ static int simple_panel_probe(struct udevice *dev)
 
 	return 0;
 }
+static int simple_panel_get_display_timing(struct udevice *dev,
+					    struct display_timing *timings)
+{
+	memcpy(timings, &boe_ev121wxm_n10_1850_timing, sizeof(*timings));
+
+	return 0;
+}
 
 static const struct panel_ops simple_panel_ops = {
 	.enable_backlight	= simple_panel_enable_backlight,
 	.set_backlight		= simple_panel_set_backlight,
+	.get_display_timing = simple_panel_get_display_timing,
 };
 
 static const struct udevice_id simple_panel_ids[] = {
@@ -115,6 +144,7 @@ static const struct udevice_id simple_panel_ids[] = {
 	{ .compatible = "lg,lb070wv8" },
 	{ .compatible = "sharp,lq123p1jx31" },
 	{ .compatible = "boe,nv101wxmn51" },
+	{ .compatible = "boe,ev121wxm-n10-1850" },
 	{ }
 };

[leavs]

It works, I forget to put one picture/logo in the uboot.