Re: [PATCH v2] drivers/fbdev: efifb: allow BAR to be moved instead of claiming it

[Peter Jones <pjones@redhat.com>]

On Mon, Jul 10, 2017 at 10:13:05PM +0100, Ard Biesheuvel wrote:
> On UEFI systems, the firmware may expose a Graphics Output Protocol (GOP)
> instance to which the efifb driver attempts to attach in order to provide
> a minimal, unaccelerated framebuffer. The GOP protocol itself is not very
> sophisticated, and only describes the offset and size of the framebuffer
> in memory, and the pixel format.
> 
> If the GOP framebuffer is provided by a PCI device, it will have been
> configured and enabled by the UEFI firmware, and the GOP protocol will
> simply point into a live BAR region. However, the GOP protocol itself does
> not describe this relation, and so we have to take care not to reconfigure
> the BAR without taking efifb's dependency on it into account.
> 
> Commit 55d728a40d36 ("efi/fb: Avoid reconfiguration of BAR that covers
> the framebuffer") attempted to do so by claiming the BAR resource early
> on, which prevents the PCI resource allocation routines from changing it.
> However, it turns out that this only works if the PCI device is not
> behind any bridges, since the bridge resources need to be claimed first.
> 
> So instead, allow the BAR to be moved, but make the efifb driver deal
> with that gracefully. So record the resource that covers the BAR early
> on, and if it turns out to have moved by the time we probe the efifb
> driver, update the framebuffer address accordingly.
> 
> While this is less likely to occur on x86, given that the firmware's
> PCI resource allocation is more likely to be preserved, this is a
> worthwhile sanity check to have in place, and so let's remove the
> 
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@linaro.org>
> ---
> v2: - use pr_info() not pr_warn() for non-error condition

Well, that settled all of my concerns:

Signed-off-by: Peter Jones <pjones@redhat.com>

> 
>  drivers/video/fbdev/efifb.c | 24 ++++++++++++--------
>  1 file changed, 15 insertions(+), 9 deletions(-)
> 
> diff --git a/drivers/video/fbdev/efifb.c b/drivers/video/fbdev/efifb.c
> index ff01bed7112f..0dd7e5eb051f 100644
> --- a/drivers/video/fbdev/efifb.c
> +++ b/drivers/video/fbdev/efifb.c
> @@ -146,6 +146,9 @@ ATTRIBUTE_GROUPS(efifb);
>  
>  static bool pci_dev_disabled;	/* FB base matches BAR of a disabled device */
>  
> +static struct resource *bar_resource;
> +static u64 bar_offset;
> +
>  static int efifb_probe(struct platform_device *dev)
>  {
>  	struct fb_info *info;
> @@ -200,6 +203,13 @@ static int efifb_probe(struct platform_device *dev)
>  		efifb_fix.smem_start |= ext_lfb_base;
>  	}
>  
> +	if (bar_resource &&
> +	    bar_resource->start + bar_offset != efifb_fix.smem_start) {
> +
> +		pr_info("efifb: PCI BAR has moved, updating fb address\n");
> +		efifb_fix.smem_start = bar_resource->start + bar_offset;
> +	}
> +
>  	efifb_defined.bits_per_pixel = screen_info.lfb_depth;
>  	efifb_defined.xres = screen_info.lfb_width;
>  	efifb_defined.yres = screen_info.lfb_height;
> @@ -364,11 +374,11 @@ static struct platform_driver efifb_driver = {
>  
>  builtin_platform_driver(efifb_driver);
>  
> -#if defined(CONFIG_PCI) && !defined(CONFIG_X86)
> +#if defined(CONFIG_PCI)
>  
>  static bool pci_bar_found;	/* did we find a BAR matching the efifb base? */
>  
> -static void claim_efifb_bar(struct pci_dev *dev, int idx)
> +static void record_efifb_bar_resource(struct pci_dev *dev, int idx, u64 offset)
>  {
>  	u16 word;
>  
> @@ -383,12 +393,8 @@ static void claim_efifb_bar(struct pci_dev *dev, int idx)
>  		return;
>  	}
>  
> -	if (pci_claim_resource(dev, idx)) {
> -		pci_dev_disabled = true;
> -		dev_err(&dev->dev,
> -			"BAR %d: failed to claim resource for efifb!\n", idx);
> -		return;
> -	}
> +	bar_resource = &dev->resource[idx];
> +	bar_offset = offset;
>  
>  	dev_info(&dev->dev, "BAR %d: assigned to efifb\n", idx);
>  }
> @@ -415,7 +421,7 @@ static void efifb_fixup_resources(struct pci_dev *dev)
>  			continue;
>  
>  		if (res->start <= base && res->end >= base + size - 1) {
> -			claim_efifb_bar(dev, i);
> +			record_efifb_bar_resource(dev, i, base - res->start);
>  			break;
>  		}
>  	}
> -- 
> 2.11.0
> 
> --
> To unsubscribe from this list: send the line "unsubscribe linux-fbdev" in
> the body of a message to majordomo@vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html

-- 
        Peter