linux-kernel - Re: [PATCH v4 2/2] efi: an sysfs interface for user to update efi firmware

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Date:	Thu, 23 Apr 2015 09:14:18 -0700
From:	James Bottomley <James.Bottomley@...senPartnership.com>
To:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:	"Kweh, Hock Leong" <hock.leong.kweh@...el.com>,
	Ming Lei <ming.lei@...onical.com>,
	Matt Fleming <matt@...sole-pimps.org>,
	"Ong, Boon Leong" <boon.leong.ong@...el.com>,
	LKML <linux-kernel@...r.kernel.org>,
	"linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
	Sam Protsenko <semen.protsenko@...aro.org>,
	Peter Jones <pjones@...hat.com>,
	Andy Lutomirski <luto@...capital.net>,
	Roy Franz <roy.franz@...aro.org>,
	Borislav Petkov <bp@...en8.de>
Subject: Re: [PATCH v4 2/2] efi: an sysfs interface for user to update efi
 firmware

On Thu, 2015-04-23 at 11:50 +0200, Greg Kroah-Hartman wrote:
> On Wed, Apr 22, 2015 at 09:11:17AM -0700, James Bottomley wrote:
> > On Wed, 2015-04-22 at 17:46 +0200, Greg Kroah-Hartman wrote:
> > > On Wed, Apr 22, 2015 at 08:35:54AM -0700, James Bottomley wrote:
> > > > On Wed, 2015-04-15 at 15:19 +0200, Greg Kroah-Hartman wrote:
> > > > > On Wed, Apr 15, 2015 at 11:32:29AM +0000, Kweh, Hock Leong wrote:
> > > > > > > -----Original Message-----
> > > > > > > From: Greg Kroah-Hartman [mailto:gregkh@...uxfoundation.org]
> > > > > > > Sent: Tuesday, April 14, 2015 10:09 PM
> > > > > > > 
> > > > > > > On Tue, Apr 14, 2015 at 05:44:56PM +0800, Kweh, Hock Leong wrote:
> > > > > > > > + */
> > > > > > > > +static void __exit efi_capsule_loader_exit(void)
> > > > > > > > +{
> > > > > > > > +	platform_device_unregister(efi_capsule_pdev);
> > > > > > > 
> > > > > > > This is not a platform device, don't abuse that interface please.
> > > > > > > 
> > > > > > > greg k-h
> > > > > > 
> > > > > > Okay, so you would recommend to use device_register() for this case?
> > > > > > Or you would think that this is more suitable to use class_register()?
> > > > > 
> > > > > A class isn't needed, you just want a device right?  So just use a
> > > > > device, but not a platform device, as that isn't what you have here.
> > > > 
> > > > Coming back to this, am I the only one confused here?  What is a
> > > > 'platform device' then?  Because if it doesn't fit a direct channel to
> > > > the platform firmware, which seems to be one of the definitions covered
> > > > in driver-model/platform.txt under devices with minimal infrastructure
> > > > then perhaps the documentation needs updating.
> > > 
> > > I don't remember the original code here at all, sorry.  I'm guessing
> > > that they were using a class, and a platform device together, which is
> > > not a good idea.  Just make a "virtual" device, as you don't need/want
> > > any of the platform device infrastructure here, you just wanted a device
> > > node and/or a way to show up in sysfs somewhere.
> > 
> > It was a platform device called efi_platform_loader and a single
> > attribute file in that device called  capsule_load.  I agree that if
> > we're going to use this for other things, we should probably have a uefi
> > directory somewhere (under firmware?) to collect everything together
> > rather than spraying random devices around.
> > 
> > > If you have some kind of "platform resource", then you can be a platform
> > > device, otherwise please don't use that api just because it seems simple
> > > to use.  Use the ones the driver core provides for you that really are
> > > just as simple (i.e. device_create()).
> > 
> > OK, so this is what I'm trying to understand.  Why isn't a pipe to
> > firmware for something a "platform resource"?  I think UEFI is in the
> > same class as ACPI which uses platform devices all over.
> 
> And I hate the fact that ACPI did that, but that ship has sailed a long
> time ago.  It "should" have been it's own bus and device type, but oh
> well.
> 
> For a "simple" bus-less device, that has no platform resources needed
> (i.e from acpi or device tree), so you don't need the infrastructure
> from the platform core, just use a simple device_create() call, that's
> what it is there for.

That's not confusing: ACPI shouldn't be a platform device, but something
that is should have a platform resource provided by ACPI (or device tree).

So I think the problem is that the documentation is wrong?  Platform
device isn't for "platform resources" like you said initially?

Or do we have a more fundamental problem: You don't use the word
"platform" the same way we do?  A "platform" to most people on this
thread is something designed to be delivered with the box that's not
amenable to user modification.  That's why we think of UEFI (and ACPI)
as platform technologies: they come with the box (often they were
specially crafted for it) and we use their services to discover stuff
and correctly configure the OS.  In this definition, almost everything
we do via UEFI manipulates "platform resources".

James


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