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

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Date:   Mon, 9 Dec 2019 14:12:42 -0500
From:   Arvind Sankar <nivedita@...m.mit.edu>
To:     Ard Biesheuvel <ardb@...nel.org>
Cc:     linux-efi@...r.kernel.org, Ingo Molnar <mingo@...nel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linux-kernel@...r.kernel.org,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Arvind Sankar <nivedita@...m.mit.edu>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        Masayoshi Mizuma <m.mizuma@...fujitsu.com>
Subject: Re: [PATCH 6/6] efi/earlycon: Remap entire framebuffer after page
 initialization

On Fri, Dec 06, 2019 at 04:55:42PM +0000, Ard Biesheuvel wrote:
> From: Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
> 
> 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?