Re: [PATCH 00/60] drm: Make all drivers to honour the nomodeset parameter

[Thomas Zimmermann]

Hi

Am 15.12.21 um 09:50 schrieb Javier Martinez Canillas:
> Hello Thomas,
>
> On 12/15/21 09:31, Thomas Zimmermann wrote:
> > Hi Javier,
> >
> > nothing wrong with your patches, but I'd like to propose slightly
> > differnt solution.
> >
> > For many USB drivers, you put the drm_firmware_drivers_only() call into
> > the probe function. For registering, these drivers use
> > module_usb_driver(), which expands to generic device-register functions.
> >
> > I'd like to propose a similar macro for DRM drivers that includes the
> > test for drm_firmware_drivers_only().
> >
> > In drm_drv.h :
> >
> >     #if defined(USB)
> >     static int drm_usb_register(struct usb_driver *usb)
> >     {
> > 	if (drm_firmware_drivers_only())
> > 		return -ENODEV;
> > 	return usb_register_driver(usb);
> >     }
> >     #define drm_module_usb_driver(__usb)
> > 	module_driver(drm_usb_register, usb_deregister)
> >     #endif
> >
> > In each of the USB-based DRM drivers, replace module_usb_driver with
> > drm_module_usb_driver.
> >
> > And then there's PCI [3] and platform drivers, [4] which can be handled
> > similarly. Many PCI drivers open-code the module init and device
>
> Thanks for the suggestion. I actually thought about this approach as well,
> since seems unnecessary to have all that duplicated logic in every driver.
>
> But at the end decided to just do the less intrusive change, because can't
> do any testing for most of the drivers.
>
> > registering with the driver-specific enable parameter. Maybe adding a
> > driver-specific register function would make sense.
>
> If I understood you correctly, suggested something similar in #dri-devel but
> danvet's suggestion [0] was to keep it simple:
>
> 16:32 javierm: danvet: yes, I don't think we would be able to do it at this point. I'll add a function pointer
>                         param to the check function so drivers can also define their own check besides nomodeset
> 16:33 danvet: javierm, uh that sounds a bit like overkill? just keep that part of the check in drivers?
> 16:33 javierm: danvet: Ok. Wanted to get rid of the duplicated code but I'm indeed over engineering this :)

An extra pointer sounds indeed like over-engineering. If we take ast for 
example, I'd just do something like this:

  static ast_pci_register_driver(struct pci_driver *pci)
  {
	if (drm_firmware_drivers_only() && ast_modeset == -1)
		return -ENODEV;
	if (ast_modeset == 0)
		return -ENODEV;

	return pci_register_driver(pci);
  }

  module_driver(&ast_pci_driver, ast_pci_register_driver,
		pci_unregister_driver)

That removes some of the boiler-plate module code without changing the 
driver's behavior.

Best regards
Thomas

> [0]: https://people.freedesktop.org/~cbrill/dri-log/?channel=dri-devel&date=2021-11-02
>
> > Best regards
> > Thomas
> Best regards,

--
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Maxfeldstr. 5, 90409 Nürnberg, Germany
(HRB 36809, AG Nürnberg)
Geschäftsführer: Ivo Totev

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