Public bug reported:
[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 this patch, it appears that the read() command sometimes fails
to receive a response, even when increasing the retry times. This could be due
to our use of a spin lock to lock the UART port in the read() function,
preventing us from calling read() immediately after a write() function.
fbf84fb368923 ("UBUNTU: SAUCE: platform/x86: dell-uart-backlight:
replace chars_in_buffer() with flush_chars()")
To fix this we only need a small delay after the write() function to
make it has time to clear its buffer.
[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.
** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: AceLan Kao (acelankao)
Status: In Progress
** Affects: linux-oem-6.5 (Ubuntu)
Importance: Undecided
Status: Invalid
** Affects: linux (Ubuntu Jammy)
Importance: Undecided
Status: Invalid
** Affects: linux-oem-6.5 (Ubuntu Jammy)
Importance: Undecided
Assignee: AceLan Kao (acelankao)
Status: In Progress
** Affects: linux (Ubuntu Mantic)
Importance: Undecided
Assignee: AceLan Kao (acelankao)
Status: In Progress
** Affects: linux-oem-6.5 (Ubuntu Mantic)
Importance: Undecided
Status: Invalid
** Also affects: linux-oem-6.5 (Ubuntu)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Jammy)
Importance: Undecided
Status: New
** Also affects: linux-oem-6.5 (Ubuntu Jammy)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Mantic)
Importance: Undecided
Status: New
** Also affects: linux-oem-6.5 (Ubuntu Mantic)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Jammy)
Status: New => Invalid
** Changed in: linux-oem-6.5 (Ubuntu Mantic)
Status: New => Invalid
** Changed in: linux (Ubuntu Mantic)
Assignee: (unassigned) => AceLan Kao (acelankao)
** Changed in: linux-oem-6.5 (Ubuntu Jammy)
Assignee: (unassigned) => AceLan Kao (acelankao)
** Changed in: linux (Ubuntu Mantic)
Status: New => In Progress
** Changed in: linux-oem-6.5 (Ubuntu Jammy)
Status: New => In Progress
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https://bugs.launchpad.net/bugs/2035299
Title:
dell-uart-backlight fails to communicate with the scalar IC somtimes.
Status in linux package in Ubuntu:
In Progress
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:
In Progress
Status in linux source package in Mantic:
In Progress
Status in linux-oem-6.5 source package in Mantic:
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 this patch, it appears that the read() command sometimes fails
to receive a response, even when increasing the retry times. This could be due
to our use of a spin lock to lock the UART port in the read() function,
preventing us from calling read() immediately after a write() function.
fbf84fb368923 ("UBUNTU: SAUCE: platform/x86: dell-uart-backlight:
replace chars_in_buffer() with flush_chars()")
To fix this we only need a small delay after the write() function to
make it has time to clear its buffer.
[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.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/2035299/+subscriptions
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