On Tue, Jun 27, 2017 at 04:19:36PM +0000, 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 the 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
> #ifdef !CONFIG_X86 that surrounds it.
>
> Signed-off-by: Ard Biesheuvel <ard.biesheuvel@xxxxxxxxxx>
> ---
> 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 b827a8113e26..6220de3e25d3 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_warn("efifb: PCI BAR has moved, updating fb address\n");
> + efifb_fix.smem_start = bar_resource->start + bar_offset;
Does this really need a pr_warn()? Seems like it should be dev_info(),
the point of the patch is to make moving it not be a problem.
--
Peter
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