Garbage UART output on RPI 4 with upstream kernel DTB
Hi,
i tried to run current U-Boot (rpi_4_32b_defconfig) on my RPi 4 with bcm2711-rpi-4-b.dtb from the upstream kernel. Unfortunately i only see garbage on the debug UART (pin 14 & 15). Using the DTB from the downstream kernel has a proper UART output. The config.txt contains debug_uart=1
I compared both and identified an offending Linux commit: ARM: dts: bcm283x: Remove brcm,bcm2835-pl011 compatible
Unfortunately reverting this patch still doesn't fix the issue. Any ideas?
Best regards Stefan
Am 20.12.19 um 14:58 schrieb Stefan Wahren:
Hi,
i tried to run current U-Boot (rpi_4_32b_defconfig) on my RPi 4 with bcm2711-rpi-4-b.dtb from the upstream kernel. Unfortunately i only see garbage on the debug UART (pin 14 & 15). Using the DTB from the downstream kernel has a proper UART output. The config.txt contains debug_uart=1
I compared both and identified an offending Linux commit: ARM: dts: bcm283x: Remove brcm,bcm2835-pl011 compatible
Unfortunately reverting this patch still doesn't fix the issue. Any ideas?
After hours of playing with the DTB, i finally found the reason why the upstream kernel DTB doesn't work with U-Boot on RPI 4. The DTS must be compiled with flag "-@".
It isn't clear to me, why this is necessary but it would be nice to make U-Boot work without this.
Regards Stefan
Best regards Stefan
Hi Stefan,
On 23/12/2019 19:51, Stefan Wahren wrote:
Am 20.12.19 um 14:58 schrieb Stefan Wahren:
Hi,
i tried to run current U-Boot (rpi_4_32b_defconfig) on my RPi 4 with bcm2711-rpi-4-b.dtb from the upstream kernel. Unfortunately i only see garbage on the debug UART (pin 14 & 15). Using the DTB from the downstream kernel has a proper UART output. The config.txt contains debug_uart=1
I compared both and identified an offending Linux commit: ARM: dts: bcm283x: Remove brcm,bcm2835-pl011 compatible
Unfortunately reverting this patch still doesn't fix the issue. Any ideas?
After hours of playing with the DTB, i finally found the reason why the upstream kernel DTB doesn't work with U-Boot on RPI 4. The DTS must be compiled with flag "-@".
It isn't clear to me, why this is necessary but it would be nice to make U-Boot work without this.
Can you provide the exact command you are using?
Regards, Matthias
Hi Matthias,
Am 23.12.19 um 21:20 schrieb Matthias Brugger:
Hi Stefan,
On 23/12/2019 19:51, Stefan Wahren wrote:
Am 20.12.19 um 14:58 schrieb Stefan Wahren:
Hi,
i tried to run current U-Boot (rpi_4_32b_defconfig) on my RPi 4 with bcm2711-rpi-4-b.dtb from the upstream kernel. Unfortunately i only see garbage on the debug UART (pin 14 & 15). Using the DTB from the downstream kernel has a proper UART output. The config.txt contains debug_uart=1
I compared both and identified an offending Linux commit: ARM: dts: bcm283x: Remove brcm,bcm2835-pl011 compatible
Unfortunately reverting this patch still doesn't fix the issue. Any ideas?
After hours of playing with the DTB, i finally found the reason why the upstream kernel DTB doesn't work with U-Boot on RPI 4. The DTS must be compiled with flag "-@".
It isn't clear to me, why this is necessary but it would be nice to make U-Boot work without this.
Can you provide the exact command you are using?
i didn't call dtc directly via command line. I just added this Makefile hack [1] to the Linux upstream tree. This will add a __symbols__ section to the DTB which is required for overlays. You can verify this with dtdiff.
Since the upstream kernel boots without the __symbols__ section, i think this garbage output issue could be fixed in u-boot.
Regards Stefan
[1] - https://github.com/raspberrypi/linux/blob/b85f76a63d5f1b13220c61244469d55487...
Regards, Matthias
On 24/12/2019 12:56, Stefan Wahren wrote:
Hi Matthias,
Am 23.12.19 um 21:20 schrieb Matthias Brugger:
Hi Stefan,
On 23/12/2019 19:51, Stefan Wahren wrote:
Am 20.12.19 um 14:58 schrieb Stefan Wahren:
Hi,
i tried to run current U-Boot (rpi_4_32b_defconfig) on my RPi 4 with bcm2711-rpi-4-b.dtb from the upstream kernel. Unfortunately i only see garbage on the debug UART (pin 14 & 15). Using the DTB from the downstream kernel has a proper UART output. The config.txt contains debug_uart=1
I compared both and identified an offending Linux commit: ARM: dts: bcm283x: Remove brcm,bcm2835-pl011 compatible
Unfortunately reverting this patch still doesn't fix the issue. Any ideas?
After hours of playing with the DTB, i finally found the reason why the upstream kernel DTB doesn't work with U-Boot on RPI 4. The DTS must be compiled with flag "-@".
It isn't clear to me, why this is necessary but it would be nice to make U-Boot work without this.
Can you provide the exact command you are using?
i didn't call dtc directly via command line. I just added this Makefile hack [1] to the Linux upstream tree. This will add a __symbols__ section to the DTB which is required for overlays. You can verify this with dtdiff.
Since the upstream kernel boots without the __symbols__ section, i think this garbage output issue could be fixed in u-boot.
Little by little I grasp what you are doing. So you compile the DTB in the kernel, then pass the blob to u-boot and add it with OF_EMBED? Is that correct?
Regards, Matthias
Am 24.12.19 um 13:38 schrieb Matthias Brugger:
On 24/12/2019 12:56, Stefan Wahren wrote:
Hi Matthias,
Am 23.12.19 um 21:20 schrieb Matthias Brugger:
Hi Stefan,
On 23/12/2019 19:51, Stefan Wahren wrote:
Am 20.12.19 um 14:58 schrieb Stefan Wahren:
Hi,
i tried to run current U-Boot (rpi_4_32b_defconfig) on my RPi 4 with bcm2711-rpi-4-b.dtb from the upstream kernel. Unfortunately i only see garbage on the debug UART (pin 14 & 15). Using the DTB from the downstream kernel has a proper UART output. The config.txt contains debug_uart=1
I compared both and identified an offending Linux commit: ARM: dts: bcm283x: Remove brcm,bcm2835-pl011 compatible
Unfortunately reverting this patch still doesn't fix the issue. Any ideas?
After hours of playing with the DTB, i finally found the reason why the upstream kernel DTB doesn't work with U-Boot on RPI 4. The DTS must be compiled with flag "-@".
It isn't clear to me, why this is necessary but it would be nice to make U-Boot work without this.
Can you provide the exact command you are using?
i didn't call dtc directly via command line. I just added this Makefile hack [1] to the Linux upstream tree. This will add a __symbols__ section to the DTB which is required for overlays. You can verify this with dtdiff.
Since the upstream kernel boots without the __symbols__ section, i think this garbage output issue could be fixed in u-boot.
Little by little I grasp what you are doing. So you compile the DTB in the kernel, then pass the blob to u-boot and add it with OF_EMBED? Is that correct?
I use a recent Raspbian image, replace the bcm2711 DTB with the upstream kernel ones (yes build with make dtbs) and kernel7.img with u-boot.bin (renamed all the other kernel binaries to make sure kernel7.img is really used). Also use a boot.scr from here, but not sure this have an influence [1]. I used the rpi_4_32b_defconfig without any modifications like OF_EMBED. I assume u-boot uses the FDT image passed by the Raspberry Pi bootloader.
[1] - https://andrei.gherzan.ro/linux/uboot-on-rpi/
Regards, Matthias
Hi Stefan,
sorry for the delay, answers inside.
On 25/12/2019 14:55, Stefan Wahren wrote:
Am 24.12.19 um 13:38 schrieb Matthias Brugger:
On 24/12/2019 12:56, Stefan Wahren wrote:
Hi Matthias,
Am 23.12.19 um 21:20 schrieb Matthias Brugger:
Hi Stefan,
On 23/12/2019 19:51, Stefan Wahren wrote:
Am 20.12.19 um 14:58 schrieb Stefan Wahren:
Hi,
i tried to run current U-Boot (rpi_4_32b_defconfig) on my RPi 4 with bcm2711-rpi-4-b.dtb from the upstream kernel. Unfortunately i only see garbage on the debug UART (pin 14 & 15). Using the DTB from the downstream kernel has a proper UART output. The config.txt contains debug_uart=1
I compared both and identified an offending Linux commit: ARM: dts: bcm283x: Remove brcm,bcm2835-pl011 compatible
Unfortunately reverting this patch still doesn't fix the issue. Any ideas?
After hours of playing with the DTB, i finally found the reason why the upstream kernel DTB doesn't work with U-Boot on RPI 4. The DTS must be compiled with flag "-@".
It isn't clear to me, why this is necessary but it would be nice to make U-Boot work without this.
Can you provide the exact command you are using?
i didn't call dtc directly via command line. I just added this Makefile hack [1] to the Linux upstream tree. This will add a __symbols__ section to the DTB which is required for overlays. You can verify this with dtdiff.
Since the upstream kernel boots without the __symbols__ section, i think this garbage output issue could be fixed in u-boot.
Little by little I grasp what you are doing. So you compile the DTB in the kernel, then pass the blob to u-boot and add it with OF_EMBED? Is that correct?
I use a recent Raspbian image, replace the bcm2711 DTB with the upstream kernel ones (yes build with make dtbs) and kernel7.img with u-boot.bin (renamed all the other kernel binaries to make sure kernel7.img is really used). Also use a boot.scr from here, but not sure this have an influence [1]. I used the rpi_4_32b_defconfig without any modifications like OF_EMBED. I assume u-boot uses the FDT image passed by the Raspberry Pi bootloader.
Yes exactly, FDT image is taken from the bootloader.
Can you please double check your config.txt especially the force_turbo and initial_trubo options.
I can see garbage on the serial console when the initial_turbo time is over (when setting force_turbo=0). If I set force_turbo=1 I don't observe this behavior.
Regards, Matthias
[1] - https://andrei.gherzan.ro/linux/uboot-on-rpi/
Regards, Matthias
participants (2)
-
Matthias Brugger -
Stefan Wahren