linux-kernel - Re: EFI Boot Stub Early Console

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Date:	Mon, 19 Mar 2012 08:47:14 +0000
From:	Matt Fleming <matt.fleming@...el.com>
To:	Shea Levy <shea@...alevy.com>
Cc:	"H. Peter Anvin" <hpa@...or.com>, linux-kernel@...r.kernel.org
Subject: Re: EFI Boot Stub Early Console

On Sun, 2012-03-18 at 08:10 -0400, Shea Levy wrote:
> Hi Matt,
> 
> On 3/18/12 7:21 AM, Matt Fleming wrote:
> > I don't think you'll need to use the graphics protocols, you should 
> > just be able to put something together using the 'output_string' 
> > function from the EFI simple text output protocol, e.g. something like 
> > this, https://lkml.org/lkml/2012/3/16/193 
> 
>  From the UEFI 2.3.1 spec:
> 
> > Prior to a call to ExitBootServices(), all of the fields of the EFI 
> > System Table are valid. After an operating system has taken control of 
> > the platform with a call to ExitBootServices(), only the Hdr, 
> > FirmwareVendor, FirmwareRevision, RuntimeServices, 
> > NumberOfTableEntries, and ConfigurationTable fields are valid.
> 
> Doesn't this mean that ConOut can't be used for the earlyprintk, since 
> any bootloader (including the bootstub) will call ExitBootServices() 
> before any printk'ing actually happens?? Or am I misunderstanding the 
> spec somehow? I suppose I could just try it and see what happens...

Oops. Good point, that isn't going to work.

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