Re: [PATCH 6/6] efi/earlycon: Remap entire framebuffer after page initialization

From: Arvind Sankar
Date: Mon Dec 09 2019 - 14:12:47 EST

On Fri, Dec 06, 2019 at 04:55:42PM +0000, Ard Biesheuvel wrote:
> From: Andy Shevchenko <andriy.shevchenko@xxxxxxxxxxxxxxx>
> When commit 69c1f396f25b
> "efi/x86: Convert x86 EFI earlyprintk into generic earlycon implementation"
> moved the x86 specific EFI earlyprintk implementation to a shared location,
> it also tweaked the behaviour. In particular, it dropped a trick with full
> framebuffer remapping after page initialization, leading to two regressions:
> 1) very slow scrolling after page initialization,
> 2) kernel hang when the 'keep_bootcon' command line argument is passed.
> Putting the tweak back fixes #2 and mitigates #1, i.e., it limits the slow
> behavior to the early boot stages, presumably due to eliminating heavy
> map()/unmap() operations per each pixel line on the screen.

Could the efi earlycon have an interaction with PCI resource allocation,
similar to what commit dcf8f5ce3165 ("drivers/fbdev/efifb: Allow BAR to
be moved instead of claiming it") fixed for efifb?