[PATCH 2/8] video/aperture: use generic code to figure out the vga default device

[PATCH 2/8] video/aperture: use generic code to figure out the vga default device

[Daniel Vetter]

Since vgaarb has been promoted to be a core piece of the pci subsystem
we don't have to open code random guesses anymore, we actually know
this in a platform agnostic way, and there's no need for an x86
specific hack. See also 1d38fe6ee6a8 ("PCI/VGA: Move vgaarb to
drivers/pci")

This should not result in any functional change, and the non-x86
multi-gpu pci systems are probably rare enough to not matter (I don't
know of any tbh). But it's a nice cleanup, so let's do it.

There's been a few questions on previous iterations on dri-devel and
irc:

- fb_is_primary_device() seems to be yet another implementation of
  this theme, and at least on x86 it checks for both
  vga_default_device OR rom shadowing. There shouldn't ever be a case
  where rom shadowing gives any additional hints about the boot vga
  device, but if there is then the default vga selection in vgaarb
  should probably be fixed. And not special-case checks replicated all
  over.

- Thomas also brought up that on most !x86 systems
  fb_is_primary_device() returns 0, except on sparc/parisc. But these
  2 special cases are about platform specific devices and not pci, so
  shouldn't have any interactions.

- Furthermore fb_is_primary_device() is a bit a red herring since it's
  only used to select the right fbdev driver for fbcon, and not for
  the fw handover dance which the aperture helpers handle. At least
  for x86 we might want to look into unifying them, but that's a
  separate thing.

v2: Extend commit message trying to summarize various discussions.

Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
Cc: Thomas Zimmermann <tzimmermann@suse.de>
Cc: Javier Martinez Canillas <javierm@redhat.com>
Cc: Helge Deller <deller@gmx.de>
Cc: linux-fbdev@vger.kernel.org
Cc: Bjorn Helgaas <bhelgaas@google.com>
Cc: linux-pci@vger.kernel.org
---
 drivers/video/aperture.c | 6 ++----
 1 file changed, 2 insertions(+), 4 deletions(-)

diff --git a/drivers/video/aperture.c b/drivers/video/aperture.c
index b009468ffdff..8835d3bc39bf 100644
--- a/drivers/video/aperture.c
+++ b/drivers/video/aperture.c
@@ -324,13 +324,11 @@ EXPORT_SYMBOL(aperture_remove_conflicting_devices);
  */
 int aperture_remove_conflicting_pci_devices(struct pci_dev *pdev, const char *name)
 {
-	bool primary = false;
+	bool primary;
 	resource_size_t base, size;
 	int bar, ret;
 
-#ifdef CONFIG_X86
-	primary = pdev->resource[PCI_ROM_RESOURCE].flags & IORESOURCE_ROM_SHADOW;
-#endif
+	primary = pdev == vga_default_device();
 
 	for (bar = 0; bar < PCI_STD_NUM_BARS; ++bar) {
 		if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))
-- 
2.40.0

Re: [PATCH 2/8] video/aperture: use generic code to figure out the vga default device

[Javier Martinez Canillas]

Daniel Vetter <daniel.vetter@ffwll.ch> writes:

> Since vgaarb has been promoted to be a core piece of the pci subsystem
> we don't have to open code random guesses anymore, we actually know
> this in a platform agnostic way, and there's no need for an x86
> specific hack. See also 1d38fe6ee6a8 ("PCI/VGA: Move vgaarb to
> drivers/pci")
>
> This should not result in any functional change, and the non-x86
> multi-gpu pci systems are probably rare enough to not matter (I don't
> know of any tbh). But it's a nice cleanup, so let's do it.
>
> There's been a few questions on previous iterations on dri-devel and
> irc:
>
> - fb_is_primary_device() seems to be yet another implementation of
>   this theme, and at least on x86 it checks for both
>   vga_default_device OR rom shadowing. There shouldn't ever be a case
>   where rom shadowing gives any additional hints about the boot vga
>   device, but if there is then the default vga selection in vgaarb
>   should probably be fixed. And not special-case checks replicated all
>   over.
>

Agreed and if there are regressions reported then could be added there.

> - Thomas also brought up that on most !x86 systems
>   fb_is_primary_device() returns 0, except on sparc/parisc. But these
>   2 special cases are about platform specific devices and not pci, so
>   shouldn't have any interactions.
>
> - Furthermore fb_is_primary_device() is a bit a red herring since it's
>   only used to select the right fbdev driver for fbcon, and not for
>   the fw handover dance which the aperture helpers handle. At least
>   for x86 we might want to look into unifying them, but that's a
>   separate thing.
>
> v2: Extend commit message trying to summarize various discussions.
>
> Signed-off-by: Daniel Vetter <daniel.vetter@intel.com>
> Cc: Thomas Zimmermann <tzimmermann@suse.de>
> Cc: Javier Martinez Canillas <javierm@redhat.com>
> Cc: Helge Deller <deller@gmx.de>
> Cc: linux-fbdev@vger.kernel.org
> Cc: Bjorn Helgaas <bhelgaas@google.com>
> Cc: linux-pci@vger.kernel.org
> ---
>  drivers/video/aperture.c | 6 ++----
>  1 file changed, 2 insertions(+), 4 deletions(-)
>
> diff --git a/drivers/video/aperture.c b/drivers/video/aperture.c
> index b009468ffdff..8835d3bc39bf 100644
> --- a/drivers/video/aperture.c
> +++ b/drivers/video/aperture.c
> @@ -324,13 +324,11 @@ EXPORT_SYMBOL(aperture_remove_conflicting_devices);
>   */
>  int aperture_remove_conflicting_pci_devices(struct pci_dev *pdev, const char *name)
>  {
> -	bool primary = false;
> +	bool primary;
>  	resource_size_t base, size;
>  	int bar, ret;
>  
> -#ifdef CONFIG_X86
> -	primary = pdev->resource[PCI_ROM_RESOURCE].flags & IORESOURCE_ROM_SHADOW;
> -#endif
> +	primary = pdev == vga_default_device();
>

Maybe enclose the check in parenthesis to make it easier to read ?

Reviewed-by: Javier Martinez Canillas <javierm@redhat.com>

-- 
Best regards,

Javier Martinez Canillas
Core Platforms
Red Hat