linux-kernel - Re: [PATCH v3 1/3] Documentation: arm: add UEFI support documentation

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Date:	Thu, 05 Dec 2013 10:55:50 +0000
From:	Grant Likely <grant.likely@...aro.org>
To:	Matt Sealey <neko@...uhatsu.net>,
	Leif Lindholm <leif.lindholm@...aro.org>
Cc:	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>, linux-efi@...r.kernel.org,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>, matt.fleming@...el.com,
	roy.franz@...aro.org, msalter@...hat.com,
	Patch Tracking <patches@...aro.org>, linaro-uefi@...aro.org,
	Mark Rutland <mark.rutland@....com>,
	Rob Landley <rob@...dley.net>, linux-doc@...r.kernel.org
Subject: Re: [PATCH v3 1/3] Documentation: arm: add UEFI support documentation

On Mon, 2 Dec 2013 13:51:22 -0600, Matt Sealey <neko@...uhatsu.net> wrote:
> > +UEFI kernel support on ARM
> > +==========================
> > +UEFI kernel support on the ARM architectures (arm and arm64) is only available
> > +when boot is performed through the stub.
> > +
> > +The stub populates the FDT /chosen node with (and the kernel scans for) the
> > +following parameters:
> > +________________________________________________________________________________
> > +Name                      | Size   | Description
> > +================================================================================
> > +linux,uefi-system-table   | 64-bit | Physical address of the UEFI System Table.
> > +--------------------------------------------------------------------------------
> > +linux,uefi-mmap-start     | 64-bit | Physical address of the UEFI memory map,
> > +                          |        | populated by the UEFI GetMemoryMap() call.
> > +--------------------------------------------------------------------------------
> > +linux,uefi-mmap-size      | 32-bit | Size in bytes of the UEFI memory map
> > +                          |        | pointed to in previous entry.
> > +--------------------------------------------------------------------------------
> > +linux,uefi-mmap-desc-size | 32-bit | Size in bytes of each entry in the UEFI
> > +                          |        | memory map.
> > +--------------------------------------------------------------------------------
> > +linux,uefi-mmap-desc-ver  | 32-bit | Version of the mmap descriptor format.
> > +--------------------------------------------------------------------------------
> > +linux,uefi-stub-kern-ver  | string | Copy of linux_banner from build.
> > +--------------------------------------------------------------------------------
> 
> This flies in the face of actually using #address-cells and
> #size-cells to define how big addresses and sizes are. You're limited
> here by the root node definitions... that's the spec.
> 
> Here's where I think this whole thing falls down as being the weirdest
> possible implementation of this. It defies logic to put this
> information in the device tree /chosen node while also attempting to
> boot the kernel using an EFI stub; the stub is going to have this
> information because it is going to have the pointer to the system
> System Table (since it was called by StartImage()). Why not stash the
> System Table pointer somewhere safe in the stub?

Everything here is about getting from the stub to the kernel. We have a
boot interface for the kernel proper. It works, and this patch set works
with it. Also, this is effectively a kernel-internal interface between
the stub and the kernel so there aren't any ABI issues that we need to
deail with.

Go ahead and propose patches for a better interface, but in the mean
time I see no reason not to merge this series.

g.
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