linux-kernel - Re: [PATCH] efifb: Add support for 64-bit frame buffer addresses

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Date:	Mon, 31 Aug 2015 11:23:31 -0400
From:	Peter Jones <pjones@...hat.com>
To:	Matt Fleming <matt@...eblueprint.co.uk>
Cc:	linux-efi@...r.kernel.org, linux-kernel@...r.kernel.org,
	linux-fbdev@...r.kernel.org, Matt Fleming <matt.fleming@...el.com>,
	Pete Hawkins <pete.hawkins@...x.com>,
	Matthew Garrett <mjg59@...f.ucam.org>,
	Chad Page <chad.page@...x.com>
Subject: Re: [PATCH] efifb: Add support for 64-bit frame buffer addresses

On Fri, Aug 28, 2015 at 01:12:19PM +0100, Matt Fleming wrote:
> From: Matt Fleming <matt.fleming@...el.com>
> 
> The EFI Graphics Output Protocol uses 64-bit frame buffer addresses
> but these get truncated to 32-bit by the EFI boot stub when storing
> the address in the 'lfb_base' field of 'struct screen_info'.
> 
> Add a 'ext_lfb_base' field for the upper 32-bits of the frame buffer
> address and set VIDEO_TYPE_CAPABILITY_64BIT_BASE when the field is
> useable.
> 
> It turns out that the reason no one has required this support so far
> is that there's actually code in tianocore to "downgrade" PCI
> resources that have option ROMs and 64-bit BARS from 64-bit to 32-bit
> to cope with legacy option ROMs that can't handle 64-bit addresses.
> The upshot is that basically all GOP devices in the wild use a 32-bit
> frame buffer address.
> 
> Still, it is possible to build firmware that uses a full 64-bit GOP
> frame buffer address. Chad did, which led to him reporting this issue.
> 
> Add support in anticipation of GOP devices using 64-bit addresses more
> widely, and so that efifb works out of the box when that happens.
> 
> Reported-by: Chad Page <chad.page@...x.com>
> Cc: Pete Hawkins <pete.hawkins@...x.com>
> Cc: Peter Jones <pjones@...hat.com>
> Cc: Matthew Garrett <mjg59@...f.ucam.org>
> Signed-off-by: Matt Fleming <matt.fleming@...el.com>

Looks good to me.

Acked-by: Peter Jones <pjones@...hat.com>

-- 
        Peter
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