linux-kernel - Re: [PATCH 04/11] video/aperture: use generic code to figure out the vga default device

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Message-ID: <e0c0e249-30bc-c310-0175-92ea379ef0d6@suse.de>
Date:   Wed, 11 Jan 2023 16:59:30 +0100
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Daniel Vetter <daniel.vetter@...ll.ch>,
        DRI Development <dri-devel@...ts.freedesktop.org>
Cc:     Intel Graphics Development <intel-gfx@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Daniel Vetter <daniel.vetter@...el.com>,
        Javier Martinez Canillas <javierm@...hat.com>,
        Helge Deller <deller@....de>, linux-fbdev@...r.kernel.org,
        Bjorn Helgaas <bhelgaas@...gle.com>, linux-pci@...r.kernel.org
Subject: Re: [PATCH 04/11] video/aperture: use generic code to figure out the
 vga default device

Hi

Am 11.01.23 um 16:41 schrieb 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.
> 
> Signed-off-by: Daniel Vetter <daniel.vetter@...el.com>
> Cc: Thomas Zimmermann <tzimmermann@...e.de>
> Cc: Javier Martinez Canillas <javierm@...hat.com>
> Cc: Helge Deller <deller@....de>
> Cc: linux-fbdev@...r.kernel.org
> Cc: Bjorn Helgaas <bhelgaas@...gle.com>
> Cc: linux-pci@...r.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 41e77de1ea82..3d8c925c7365 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();

vga_default_device() is part of vgaarb and can return NULL. [1] That new 
test is likely to be incorrect on many systems.

I suggest to implement a helper like fb_is_primary_device() on x86: it 
uses the default VGA if set, or falls back to the original test. [2]

It's noteworthy that on most architectures, fb_is_primary_device() 
returns 0. But at least on Sparc [3] and some Parisc [4] machines, it 
does not.

I've long wanted to rework this helper anyway. So this is a good 
opportunity.

Best regards
Thomas

[1] 
https://elixir.bootlin.com/linux/latest/source/include/linux/vgaarb.h#L69
[2] 
https://elixir.bootlin.com/linux/latest/source/arch/x86/video/fbdev.c#L14
[3] 
https://elixir.bootlin.com/linux/latest/source/arch/sparc/include/asm/fb.h#L18
[4] 
https://elixir.bootlin.com/linux/latest/source/drivers/video/console/sticore.c#L1153


>   
>   	for (bar = 0; bar < PCI_STD_NUM_BARS; ++bar) {
>   		if (!(pci_resource_flags(pdev, bar) & IORESOURCE_MEM))

-- 
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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