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

- From: Bartlomiej Zolnierkiewicz \<hidden\>
- Date: 2017-07-12 10:00:46 
- List: linux-fbdev
- Page: https://ratatoskr.run/linux-fbdev/2017/07/13377613
- Thread: https://ratatoskr.run/linux-pci/2017/07/13377609/t.md

```text
On Monday, July 10, 2017 10:13:05 PM 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

It still cuts the patch description early..

> Signed-off-by: Ard Biesheuvel <redacted>

From fbdev's side:

Acked-by: Bartlomiej Zolnierkiewicz <redacted>

> ---
> v2: - use pr_info() not pr_warn() for non-error condition

Best regards,
--
Bartlomiej Zolnierkiewicz
Samsung R&D Institute Poland
Samsung Electronics

```