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

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Message-ID: <20150422154620.GA32576@kroah.com>
Date:	Wed, 22 Apr 2015 17:46:20 +0200
From:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>
To:	James Bottomley <James.Bottomley@...senPartnership.com>
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 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.

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()).

thanks,

greg k-h
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