Hi
Am 07.11.22 um 14:57 schrieb Helge Deller:
On 11/7/22 11:49, Thomas Zimmermann wrote:
quoted
Support the kernel's nomodeset parameter for all PCI-based fbdev
drivers that use aperture helpers to remove other, hardware-agnostic
graphics drivers.
The parameter is a simple way of using the firmware-provided scanout
buffer if the hardware's native driver is broken.
Nah... it's probably not broken, but you want it disabled in order
to use the DRM driver instead?
No, it's really for broken native drivers or any kind of problematic modesetting. Most DRM drivers already respect the nomodeset option and won't load when given. All you'd get are the generic drivers, such as simpledrm, efifb or simplefb.
There are better options of configuring video output on the kernel command line. But as graphics output is such a fundamental feature to using a computer, we found that a simple and easy option to workaround erroneous systems would benefit DRM users; hence the nomodeset parameter.
As fbdev drivers also do modesetting, supporting the parameter simply unifies the behavior.
quoted
The same effect
could be achieved with per-driver options, but the importance of the
graphics output for many users makes a single, unified approach
worthwhile.
With nomodeset specified, the fbdev driver module will not load. This
unifies behavior with similar DRM drivers. In DRM helpers, modules
first check the nomodeset parameter before registering the PCI
driver. As fbdev has no such module helpers, we have to modify each
driver individually.
Ok.
quoted
The name 'nomodeset' is slightly misleading, but has been chosen for
historical reasons. Several drivers implemented it before it became a
general option for DRM. So keeping the existing name was preferred over
introducing a new one.
quoted
diff --git a/drivers/video/fbdev/aty/aty128fb.c b/drivers/video/fbdev/aty/aty128fb.c
index 57e398fe7a81c..1a26ac2865d65 100644
--- a/drivers/video/fbdev/aty/aty128fb.c
+++ b/drivers/video/fbdev/aty/aty128fb.c
@@ -2503,7 +2504,12 @@ static int aty128fb_init(void)
{
#ifndef MODULE
char *option = NULL;
+#endif
+
+ if (video_firmware_drivers_only())
+ return -ENODEV;
I think it makes sense to give at least some info, why a specific
driver wasn't loaded, e.g. something like this kernel message:
aty128fb: Driver disabled due to "nomodeset" kernel parameter.
If you e.g. change the function video_firmware_drivers_only()
to become video_firmware_drivers_only(const char *drivername)
then you could print such a message in video_firmware_drivers_only()
Well, we do have such a message in disable_modeset() already. [1]
[1] https://elixir.bootlin.com/linux/latest/source/drivers/gpu/drm/drm_nomodeset.c#L18
And I don't like very much the name of function video_firmware_drivers_only(),
but don't have any other better idea right now either...
It's part of the 'video' module, hence the prefix. The 'nomodeset' option used to be implemented in several DRM drivers. It's an awful name, but we didn't want to remove it or introduce a new one for the same feature. So we kept nomodeset for all of DRM. Then we started bikeshedding the function name that returns the setting. And firmware-drivers-only is the best description of what is happening here. So that's how the name happend.
Best regards
Thomas
Helge
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev