Re: [PATCH] drm/xe: Support 'nomodeset' kernel command-line option

[Thomas Zimmermann <tzimmermann@suse.de>]

Hi

Am 21.08.24 um 16:29 schrieb Jani Nikula:
> On Wed, 21 Aug 2024, Gustavo Sousa <gustavo.sousa@intel.com> wrote:
>> Quoting Thomas Zimmermann (2024-08-21 10:56:59-03:00)
>>> Setting 'nomodeset' on the kernel command line disables all graphics
>>> drivers with modesetting capabilities; leaving only firmware drivers,
>>> such as simpledrm or efifb.
>>>
>>> Most DRM drivers automatically support 'nomodeset' via DRM's module
>>> helper macros. In xe, which uses regular module_init(), manually call
>>> drm_firmware_drivers_only() to test for 'nomodeset'. Do not register
>>> the driver if set.
>>>
>>> Signed-off-by: Thomas Zimmermann <tzimmermann@suse.de>
>>> ---
>>> drivers/gpu/drm/xe/xe_module.c | 5 +++++
>>> 1 file changed, 5 insertions(+)
>>>
>>> diff --git a/drivers/gpu/drm/xe/xe_module.c b/drivers/gpu/drm/xe/xe_module.c
>>> index 923460119cec..60fb7dd26903 100644
>>> --- a/drivers/gpu/drm/xe/xe_module.c
>>> +++ b/drivers/gpu/drm/xe/xe_module.c
>>> @@ -8,6 +8,8 @@
>>> #include <linux/init.h>
>>> #include <linux/module.h>
>>>
>>> +#include <drm/drm_module.h>
>>> +
>>> #include "xe_drv.h"
>>> #include "xe_hw_fence.h"
>>> #include "xe_pci.h"
>>> @@ -92,6 +94,9 @@ static int __init xe_init(void)
>>> {
>>>          int err, i;
>>>
>>> +        if (drm_firmware_drivers_only())
>>> +                return -ENODEV;
>>> +
>> Hm... But what if xe is to be used only for compute or render? Shouldn't
>> we handle this somewhere else?
> The question becomes, what does "nomodeset" really mean here?

That function's name 'firmware drivers only' says it better than the 
option's name. We used 'nomodeset', because it was there already and had 
the correct semantics.

>
> See what i915 does in i915_module.c.

i915 and the other drivers for PCI-based hardware don't load at all. 
Drivers for external displays (e.g., SPI, USB) ignore nomodeset, as 
these displays are not initialized by firmware.

Best regards
Thomas

>
> Cc: Sima.
>
> BR,
> Jani.
>
>
>
>> Taking a quick look, xe_display_probe() might be a good candidate?
>>
>> --
>> Gustavo Sousa
>>
>>>          for (i = 0; i < ARRAY_SIZE(init_funcs); i++) {
>>>                  err = init_funcs[i].init();
>>>                  if (err) {
>>> -- 
>>> 2.46.0
>>>

-- 
--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)