linux-kernel - Re: [Intel-gfx] [PATCH v3 3/9] PCI/VGA: Switch to aperture_contain_firmware_fb

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Message-ID: <20230719204314.GA512532@bhelgaas>
Date:   Wed, 19 Jul 2023 15:43:14 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Sui Jingfeng <sui.jingfeng@...ux.dev>
Cc:     David Airlie <airlied@...il.com>, linux-fbdev@...r.kernel.org,
        Sui Jingfeng <suijingfeng@...ngson.cn>, kvm@...r.kernel.org,
        intel-gfx@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
        dri-devel@...ts.freedesktop.org, amd-gfx@...ts.freedesktop.org,
        linux-pci@...r.kernel.org
Subject: Re: [Intel-gfx] [PATCH v3 3/9] PCI/VGA: Switch to
 aperture_contain_firmware_fb_nonreloc()

[+cc linux-pci; I don't apply or ack PCI patches unless they appear there]

On Wed, Jul 12, 2023 at 12:43:04AM +0800, Sui Jingfeng wrote:
> From: Sui Jingfeng <suijingfeng@...ngson.cn>
> 
> The observation behind this is that we should avoid accessing the global
> screen_info directly. Call the aperture_contain_firmware_fb_nonreloc()
> function to implement the detection of whether an aperture contains the
> firmware FB.

Because it's better to access the global screen_info from
aperture_contain_firmware_fb_nonreloc()?  The reasoning here is not
super clear to me.

> This patch helps to decouple the determination from the implementation.
> Or, in other words, we intend to make the determination opaque to the
> caller. The determination may choose to be arch-dependent or
> arch-independent. But vgaarb, as a consumer of the determination,
> shouldn't care how the does determination is implemented.

"how the determination ..."  (drop the "does")

Are you saying that aperture_contain_firmware_fb_nonreloc() might be
arch-dependent?  Are there multiple callers?  Or does this just move
code from one place to a more appropriate place?

> Signed-off-by: Sui Jingfeng <suijingfeng@...ngson.cn>
> ---
>  drivers/pci/vgaarb.c | 19 ++++---------------
>  1 file changed, 4 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/pci/vgaarb.c b/drivers/pci/vgaarb.c
> index bf96e085751d..953daf731b2c 100644
> --- a/drivers/pci/vgaarb.c
> +++ b/drivers/pci/vgaarb.c
> @@ -14,6 +14,7 @@
>  #define vgaarb_info(dev, fmt, arg...)	dev_info(dev, "vgaarb: " fmt, ##arg)
>  #define vgaarb_err(dev, fmt, arg...)	dev_err(dev, "vgaarb: " fmt, ##arg)
>  
> +#include <linux/aperture.h>
>  #include <linux/module.h>
>  #include <linux/kernel.h>
>  #include <linux/pci.h>
> @@ -26,7 +27,6 @@
>  #include <linux/poll.h>
>  #include <linux/miscdevice.h>
>  #include <linux/slab.h>
> -#include <linux/screen_info.h>
>  #include <linux/vt.h>
>  #include <linux/console.h>
>  #include <linux/acpi.h>
> @@ -558,20 +558,11 @@ void vga_put(struct pci_dev *pdev, unsigned int rsrc)
>  }
>  EXPORT_SYMBOL(vga_put);
>  
> +/* Select the device owning the boot framebuffer if there is one */
>  static bool vga_is_firmware_default(struct pci_dev *pdev)
>  {
>  #if defined(CONFIG_X86) || defined(CONFIG_IA64)
> -	u64 base = screen_info.lfb_base;
> -	u64 size = screen_info.lfb_size;
>  	struct resource *r;
> -	u64 limit;
> -
> -	/* Select the device owning the boot framebuffer if there is one */
> -
> -	if (screen_info.capabilities & VIDEO_CAPABILITY_64BIT_BASE)
> -		base |= (u64)screen_info.ext_lfb_base << 32;
> -
> -	limit = base + size;
>  
>  	/* Does firmware framebuffer belong to us? */
>  	pci_dev_for_each_resource(pdev, r) {
> @@ -581,10 +572,8 @@ static bool vga_is_firmware_default(struct pci_dev *pdev)
>  		if (!r->start || !r->end)
>  			continue;
>  
> -		if (base < r->start || limit >= r->end)
> -			continue;
> -
> -		return true;
> +		if (aperture_contain_firmware_fb_nonreloc(r->start, r->end))
> +			return true;
>  	}
>  #endif
>  	return false;
> -- 
> 2.25.1
>