Hi,
On 02-09-19 07:17, Mantas Mikulėnas wrote:
On Mon, Sep 2, 2019 at 7:34 AM Chris Murphy <lists@xxxxxxxxxxxxxxxxx <mailto:lists@xxxxxxxxxxxxxxxxx>> wrote:
systemd-243~rc2-2.fc31.x86_64
kernel-5.3.0-0.rc6.git1.1.fc32.x86_64
This might be a regression, at least I don't remember this happening
before. I can use the expected keys for built-in display brightness,
and built-in keyboard brightness. But the service unit fails with an
out of the box installation.
[chris@fmac ~]$ sudo systemctl status
systemd-backlight@backlight:acpi_video0.service
● systemd-backlight@backlight:acpi_video0.service - Load/Save Screen
Backlight Brightness of backlight:acpi_video0
Loaded: loaded (/usr/lib/systemd/system/systemd-backlight@.service;
static; vendor preset: disabled)
Active: failed (Result: exit-code) since Sun 2019-09-01 19:57:37
MDT; 8min ago
Docs: man:systemd-backlight@.service(8)
Process: 667 ExecStart=/usr/lib/systemd/systemd-backlight load
backlight:acpi_video0 (code=exited, status=1/FAILURE)
Main PID: 667 (code=exited, status=1/FAILURE)
Sep 01 19:57:37 fmac.local systemd[1]: Starting Load/Save Screen
Backlight Brightness of backlight:acpi_video0...
Sep 01 19:57:37 fmac.local systemd-backlight[667]: Failed to get
backlight or LED device 'backlight:acpi_video0': No such device
Sep 01 19:57:37 fmac.local systemd[1]:
systemd-backlight@backlight:acpi_video0.service: Main process exited,
code=exited, status=1/FAILURE
Sep 01 19:57:37 fmac.local systemd[1]:
systemd-backlight@backlight:acpi_video0.service: Failed with result
'exit-code'.
Sep 01 19:57:37 fmac.local systemd[1]: Failed to start Load/Save
Screen Backlight Brightness of backlight:acpi_video0.
[chris@fmac ~]$
# find /sys -name "*video0*"
/sys/class/video4linux/video0
/sys/devices/pci0000:00/0000:00:1a.7/usb1/1-2/1-2:1.0/video4linux/video0
# ls -l /sys/class/backlight/
total 0
lrwxrwxrwx. 1 root root 0 Sep 1 19:57 gmux_backlight ->
../../devices/pnp0/00:03/backlight/gmux_backlight
lrwxrwxrwx. 1 root root 0 Sep 1 19:57 intel_backlight ->
../../devices/pci0000:00/0000:00:02.0/drm/card0/card0-LVDS-1/intel_backlight
Could it be that acpi_backlight is loaded at first, but gets replaced by intel_backlight before systemd could react?
Maybe, the gmux_backlight suggests that this is a macbook.
On normal machines, what you say will not happen because
linux/drivers/acpi/acpi_video.c has:
static int __init acpi_video_init(void)
{
...
if (intel_opregion_present())
return 0;
And then later the i915 kms driver tells acpi_video it is ok
to actual register by calling acpi_video_register()
But on mac Books there also is the gmux, and I see that the gmux
code also calls acpi_video_register(), possibly before the i915
driver is setup, which would trigger the race you suggest where
acpi_video.c registers it backlight interface, which is only done
if there are no "native" preferred backlight interfaces and then
i915 comes along, registers its "native" backlight interface and
the acpi backlight code removes its acpi_video0 in response to
that.
So yes this seems like a race, which only gets seen on macbooks.
Regards,
Hans
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