** Also affects: linux (Ubuntu Noble)
Importance: Undecided
Assignee: AceLan Kao (acelankao)
Status: In Progress
** Also affects: linux-oem-6.5 (Ubuntu Noble)
Importance: Undecided
Status: Invalid
** Changed in: linux (Ubuntu Noble)
Status: In Progress => Triaged
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https://bugs.launchpad.net/bugs/2035299
Title:
dell-uart-backlight fails to communicate with the scalar IC somtimes.
Status in HWE Next:
New
Status in linux package in Ubuntu:
Triaged
Status in linux-oem-6.5 package in Ubuntu:
Invalid
Status in linux source package in Jammy:
Invalid
Status in linux-oem-6.5 source package in Jammy:
Fix Released
Status in linux source package in Mantic:
In Progress
Status in linux-oem-6.5 source package in Mantic:
Invalid
Status in linux source package in Noble:
Triaged
Status in linux-oem-6.5 source package in Noble:
Invalid
Bug description:
[Impact]
Boots up the system and sometimes we can see below messages and that leads to
backlight driver doesn't get loaded.
[ 86.424880] dell_uart_backlight:dell_uart_get_display_mode:tx: 6a 10 85
[ 86.603936] [7439] dell_uart_backlight:dell_uart_get_display_mode:rx: NULL
[ 87.596047] dell_uart_backlight:dell_uart_get_display_mode:tx: 6a 10 85
[ 87.775209] [7439] dell_uart_backlight:dell_uart_get_display_mode:rx: NULL
[Fix]
After applying the patch below, it seems that the read() command may fail to
receive a response, even when increasing the retry times. It never gets a
response when it fails.
fbf84fb368923 ("UBUNTU: SAUCE: platform/x86: dell-uart-backlight:
replace chars_in_buffer() with flush_chars()")
To fix this, try adding a small delay after the write() function as a
workaround.
[Test case]
1. Add dell_uart_backlight.dyndbg="+pt" to the kernel cmdline
2. Boots up the system and check dmesg
3. Make sure there is no dell_uart_backlight rx NULL message in dmesg
4. Try to unload/reload dell_uart_backlight couple times and check dmesg again
[Where problems could occur]
sleep for 1ms is pretty short that it's not possible to lead to messages loss.
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