How to set LVDS as default panel

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How to set LVDS as default panel

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xiaochao0131
Contributor III

I installed ubuntu Image in my iMX6 sabre lite board.
I want to use LVDS as default output, so I changed the u-boot environment as below:

setenv bootargs_mmc 'setenv bootargs ${bootargs} root=/dev/mmcblk1p1 rootwait rw video=mxcfb0:dev=ldb,1920x1080M@60,if=RGB666', then saveenv and reset.

I saw the log from concole is "ldb ldb.14: failed to find valid LVDS channel".

The HDMI output can work normally. In the uboot, it shows:

U-Boot 2016.03-20415-ged95621 (Jul 07 2016 - 17:28:42 -0700), Build: jenkins-ub4

CPU:   Freescale i.MX6Q rev1.2 at 792 MHz

Reset cause: POR

Board: SABRE Lite

I2C:   ready

DRAM:  1 GiB

MMC:   FSL_SDHC: 0, FSL_SDHC: 1

SF: Detected SST25VF016B with page size 256 Bytes, erase size 4 KiB, total 2 MiB

auto-detected panel 1280x720M@60

Display: hdmi:1280x720M@60 (1280x720)

In:    serial

Out:   serial                                                                  

Err:   serial                                                                  

Net:   Micrel ksz9021 at 6                                                     

FEC [PRIME]                                                                    

Error: FEC address not set.                                                    

, usb_ether                                                                    

Hit any key to stop autoboot:  0 

How can I change the default panel from HDMI to LVDS?

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gary_bisson
Senior Contributor III

Hi,

Please read our blog posts entirely. The image you are using comes from here:

https://boundarydevices.com/mx-linux-kernel-3-14-52/

At the end of the post it is said:

"

U-Boot is in charge of setting the display parameters in the device tree. So it requires to use U-Boot v2015.07 or higher. Please make sure to read our blog post about this release:

https://boundarydevices.com/compiling-latest-u-boot-for-i-mx6-2015-edition

"

Everything is explained there. Hope this helps.

Regards,

Gary

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durmu_kurtulu_
Contributor IV

Hi,

What you changed is bootargs for Linux kernel and therefore Linux will try to use LVDS port as display. However what you show us is the output of u-boot and it does not have much to do with Linux display configuration.

You mention "ldb ldb.14: failed to find valid LVDS channel".

Are you sure LVDS port is configured correctly? Show us your device tree.

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xiaochao0131
Contributor III

Hi,

The uboot and Ubuntu image is downloaded from official website, I did not change anything yet, Do you mean I need to download the BSP sourcecode and modify the LVDS config file then rebuild BSP?

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durmu_kurtulu_
Contributor IV

Hi,

If you want to change your U-boot default display, you should definitely modify U-boot source.

However, if you just want to change Ubuntu display, what you did seems correct to me. But because you are getting that ldb error, the only reason I can think of is that LVDS is not enabled in device tree.

What does the documentation say? LVDS enabled by default?

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xiaochao0131
Contributor III

I just want to change Ubuntu display, I saw the log in serial console shows that "LVDS disabled", how to enable LVDS? which document can be referenced for the issue?

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durmu_kurtulu_
Contributor IV

You said that U-boot and Ubuntu image are downloaded from official website. Surely, there must be some documentation there?

If LVDS is disabled, you should either find a precompiled .dts file with LVDS enabled for your board or you should do that yourself. Download kernel source, enable LVDS in device tree, compile and deploy.

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xiaochao0131
Contributor III

BTW, I run printenv in u-boot, the log shows as below:

cmd_hdmi=fdt set fb_hdmi status okay;fdt set fb_hdmi mode_str 1280x720M@60;

cmd_lcd=fdt set fb_lcd status disabled

cmd_lvds=fdt set fb_lvds status disabled;fdt set ldb/lvds-channel@0 status disab

led

the lvds status is disabled, can I enable it in u-boot?

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xiaochao0131
Contributor III

When power on the board, I noticed that the backlight of LVDS panel flick some times.

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xiaochao0131
Contributor III

Below is the log:

U-Boot 2016.03-20415-ged95621 (Jul 07 2016 - 17:28:42 -0700), Build: jenkins-ub4

CPU:   Freescale i.MX6Q rev1.2 at 792 MHz

Reset cause: POR

Board: SABRE Lite

I2C:   ready

DRAM:  1 GiB

MMC:   FSL_SDHC: 0, FSL_SDHC: 1

SF: Detected SST25VF016B with page size 256 Bytes, erase size 4 KiB, total 2 MiB

Display: hdmi:1280x720M@60 (1280x720)

In:    serial

Out:   serial

Err:   serial                                                                  

Net:   Micrel ksz9021 at 6                                                     

FEC [PRIME]                                                                    

Error: FEC address not set.                                                    

, usb_ether                                                                    

Hit any key to stop autoboot:  0                                               

AHCI 0001.0300 32 slots 1 ports 3 Gbps 0x1 impl SATA mode                      

flags: ncq stag pm led clo only pmp pio slum part                              

No port device detected!                                                       

** Bad device size - sata 0 **                                                 

                                                                               

SATA device 1: unknown device                                                  

** Bad device sata 1 **                                                        

MMC: no card present                                                           

MMC: no card present                                                           

** Bad device mmc 0 **                                                         

switch to partitions #0, OK                                                    

mmc1 is current device                                                         

4437 bytes read in 29 ms (149.4 KiB/s)                                         

## Executing script at 10008000                                                

** File not found uEnv.txt **                                                  

42869 bytes read in 1207 ms (34.2 KiB/s)                                       

only CEA modes allowed on HDMI port                                            

----------- trying to load /initrd.img                                         

2317536 bytes read in 280 ms (7.9 MiB/s)                                       

5499904 bytes read in 499 ms (10.5 MiB/s)                                      

Kernel image @ 0x10800000 [ 0x000000 - 0x53ec00 ]                              

## Flattened Device Tree blob at 13000000                                      

   Booting using the fdt blob at 0x13000000                                    

   reserving fdt memory region: addr=13000000 size=b000                        

   Using Device Tree in place at 13000000, end 1300dfff                        

                                                                               

Starting kernel ...                                                            

                                                                               

ldb ldb.14: failed to find valid LVDS channel                                  

fec 2188000.ethernet (unregistered net_device): Invalid MAC address: 00:00:00:00

snvs_rtc 20cc034.snvs-rtc-lp: can't get snvs-rtc clock                         

imx6q-pcie 1ffc000.pcie: phy link never came up                                

imx6q-pcie 1ffc000.pcie: Failed to bring link up!                              

imx6q-pcie 1ffc000.pcie: failed to initialize host                             

ili210x_i2c 2-0041: i2c transfer failed                                        

ili210x_i2c 2-0041: Failed to get firmware version, err: -5                    

tsc2004_reset: write_cmd -5                                                    

tsc2004 2-0048: Failed to reset TSC -5                                         

adv7180 2-0020: adv7180_read:read reg error: reg=11 ret=-5                     

egalax_ts 2-0004: Failed to read firmware version                              

ft5x06-ts 2-0038: ft5x06: Could not detect touch screen -19.                   

tc358743_read_reg:reg=0 ret=-5                                                 

tc358743_probe:cannot find camera                                              

tc358743_probe: failed, error=-19                                              

ov5640_read_reg:write reg error:reg=300a                                       

mxc_v4l_open: Mxc Camera no sensor ipu0/csi0                                   

mxc_v4l_open: Mxc Camera no sensor ipu1/csi0                                   

mxc_v4l_open: Mxc Camera no sensor ipu0/csi0                                   

mxc_v4l_open: Mxc Camera no sensor ipu1/csi1                                   

update_device_addr: ov5640_mipi ret=-5                                         

ov5640_read_reg(mipi):reg=300a ret=-5                                          

update_device_addr: ov5642 ret=-5                                              

ov5642_read_reg:write reg error:reg=300a                                       

[ OK ]                                                                         

saned disabled; edit /etc/default/saned                                        

                                                                               

Ubuntu 14.04.4 LTS nitrogen ttymxc1

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