linux-kernel - Re: [PATCH] x86/efi: Add EFI framebuffer earlyprintk support

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Date:	Thu, 10 Oct 2013 19:45:21 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Peter Jones <pjones@...hat.com>
Cc:	Matt Fleming <matt@...sole-pimps.org>, linux-efi@...r.kernel.org,
	linux-kernel@...r.kernel.org,
	Matt Fleming <matt.fleming@...el.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH] x86/efi: Add EFI framebuffer earlyprintk support


* Peter Jones <pjones@...hat.com> wrote:

> On Thu, Oct 10, 2013 at 07:28:44PM +0200, Ingo Molnar wrote:
> > 
> > Is a non-32-bit framebuffer a possibility? If yes then it might be nice to 
> > emit an informative printk() here, so that users who try to enable EFI 
> > early-printk can at least see why it's not working. (Assuming they get to 
> > look at regular printk output, on a safe/working kernel.)
> 
> Not really - the spec allows RGBx, BGRx, and for custom bit masks, but
> they're define like:
> 
> typedef struct {
> 	UINT32 RedMask;
> 	UINT32 GreenMask;
> 	UINT32 BlueMask;
> 	UINT32 ReservedMask;
> } EFI_PIXEL_BITMASK;

Hm, that structure does not show up anywhere in the kernel that I can see.

How are those mask values to be interpreted? As regular bitmasks? Are bits 
in the masks set to 1 consecutively, starting from bit 0?

Also, the main question would be, what is the typical value for 
si->lfb_depth. 32 on almost all EFI systems? All around the map? Depends 
on what graphics state the EFI bootloader passes us?

Thanks,

	Ingo
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