Re: [PATCH 4/5] [SCSI] Do not use platform_bus as a parent

From: Greg Kroah-Hartman
Date: Sat Jul 26 2014 - 16:11:56 EST

On Fri, Jul 25, 2014 at 07:46:56AM -0700, James Bottomley wrote:
> On Fri, 2014-07-25 at 15:23 +0100, Pawel Moll wrote:
> > The host devices without a parent were "forcefully adopted"
> > by platform bus. This patch removes this assignment. In
> > effect the dev_dev may be NULL now, which means ISA.
> >
> > Cc: James E.J. Bottomley <JBottomley@xxxxxxxxxxxxx>
> > Cc: linux-scsi@xxxxxxxxxxxxxxx
> > Signed-off-by: Pawel Moll <pawel.moll@xxxxxxx>
> > ---
> >
> > This patch is a part of effort to remove references to platform_bus
> > and make it static.
> >
> > James, could you please have a look and advice if the change is
> > correct? Would you happen to know the "real reasons" behind
> > using the root platform_bus device a parent?
> Yes, for DMA purposes, the parent cannot now be NULL; we'll get a panic
> in the DMA transfers if it is. A lot of the legacy ISA device on x86
> and I thought some ARM SOC devices don't pass in the parent device, so
> we hang them off a known parent.

The "generic" platform bus device is not a "known parent". I don't
understand the difference between just setting the parent to be NULL,
which will then have a "proper" parent pointer filled in by the driver
core when the device is registered, or faking it out here. What is the

In the end, the device always ends up with a parent pointer, right?


greg k-h
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