linux-kernel - Re: [PATCH 1/4] Documentation: arm: [U]EFI runtime services

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Message-ID: <20130626140459.GB9078@rocoto.smurfnet.nu>
Date:	Wed, 26 Jun 2013 16:04:59 +0200
From:	Leif Lindholm <leif.lindholm@...aro.org>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-efi@...r.kernel.org,
	"linux-doc@...r.kernel.org" <linux-doc@...r.kernel.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	"patches@...aro.org" <patches@...aro.org>,
	"H. Peter Anvin" <hpa@...ux.intel.com>,
	Thomas Gleixner <tglx@...utronix.de>, matt.fleming@...el.com
Subject: Re: [PATCH 1/4] Documentation: arm: [U]EFI runtime services

On Wed, Jun 26, 2013 at 02:13:39PM +0100, Grant Likely wrote:
> > diff --git a/Documentation/arm/uefi.txt b/Documentation/arm/uefi.txt
> > +It (early) parses the FDT for the following parameters:
> 
> Need to state which node these properties can be found in. I recommend /chosen

Will do.
 
> I would also prefix all of the following properties with "linux,"
> since they are very much about what the Linux kernel needs for
> booting. EFI stub will be creating these properties specifically for
> Linux, and the LinuxLoader should do the same (until we eventually
> kill it).
 
And that.

> > +- 'efi-system-table':
> > +  Physical address of the system table. (required)
> 
> Need to mention the size of this address. Is it 64 bit or 32 bit? I
> would follow the lead of 'linux,initrd-start' here and make the size
> of property the size of the address. ie. If it is 8 bytes long, then
> it is a 64 bit address.
 
Currently, it's a 4-byte address.
Although technically possible to be >32-bit in an LPAE system, the 1:1
mappign requirement of the UEFI spec forces it to reside in the lower
4GB on a 32-bit system.

> > +- 'efi-runtime-mmap':
> > +  Physical address of an EFI memory map, containing at least
> > +  the regions to be preserved. (required)
> > +- 'efi-runtime-mmap-size':
> > +  Size in bytes of the provided memory map. (required)
> 
> I would collapse the above two properties into a single property that
> actually contains the memory map instead of pointing to it. You will
> also need to specify the exact format of the data in this property.
 
Ok, that makes sense.

Hmm. The data is an array of struct EFI_MEMORY_DESCRIPTOR entries,
known in Linux as efi_memory_desc_t. Is that a good enough description?

> > +- 'efi-mmap-desc-size':
> > +  Size of each descriptor in the memory map. (override default)
> > +- 'efi-mmap-desc-ver':
> > +  Memory descriptor format version. (override default)
> 
> I don't understand how these properties will actually work. What
> changes in the parsing if these properties are set?
 
I guess the intended use is that these options would permit you to
append new fields to the struct and have old code correctly parse the
array anyway.

/
    Leif
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