From: gregkh@linuxfoundation•org (Greg Kroah-Hartman)
To: linux-arm-kernel@lists•infradead.org
Subject: [PATCH 4/5] [SCSI] Do not use platform_bus as a parent
Date: Sun, 27 Jul 2014 08:07:20 -0700 [thread overview]
Message-ID: <20140727150720.GC1723@kroah.com> (raw)
In-Reply-To: <1406433177.11069.3.camel@jarvis>
On Sun, Jul 27, 2014 at 07:52:57AM +0400, James Bottomley wrote:
> On Sat, 2014-07-26 at 13:11 -0700, Greg Kroah-Hartman wrote:
> > 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@parallels•com>
> > > > Cc: linux-scsi at vger.kernel.org
> > > > Signed-off-by: Pawel Moll <pawel.moll@arm•com>
> > > > ---
> > > >
> > > > 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
> > difference?
>
> If you set the parent to NULL, the host template dma_dev will end up
> NULL as well and that will trigger a NULL deref panic in the dma segment
> routines.
>
> If you want to remove platform_bus, we have to have a well known device
> to set dma_dev to at scsi_host_add time.
Why not set the dma_dev after you call device_add()? That way you will
pick up the right parent no matter what.
> > In the end, the device always ends up with a parent pointer, right?
>
> The parent pointer isn't the problem ... assigning the correct dma
> device is.
Ah, ok, it's a scsi core thing, not a driver core thing, that's less
confusing now. For a "fallback" of a platform device, if you switch the
lines around you should be fine, something like this patch perhaps:
diff --git a/drivers/scsi/hosts.c b/drivers/scsi/hosts.c
index 3cbb57a8b846..d8d3b294f5bc 100644
--- a/drivers/scsi/hosts.c
+++ b/drivers/scsi/hosts.c
@@ -218,16 +218,16 @@ int scsi_add_host_with_dma(struct Scsi_Host *shost, struct device *dev,
goto fail;
if (!shost->shost_gendev.parent)
- shost->shost_gendev.parent = dev ? dev : &platform_bus;
- if (!dma_dev)
- dma_dev = shost->shost_gendev.parent;
-
- shost->dma_dev = dma_dev;
+ shost->shost_gendev.parent = dev;
error = device_add(&shost->shost_gendev);
if (error)
goto out;
+ if (!dma_dev)
+ dma_dev = shost->shost_gendev.parent;
+ shost->dma_dev = dma_dev;
+
pm_runtime_set_active(&shost->shost_gendev);
pm_runtime_enable(&shost->shost_gendev);
device_enable_async_suspend(&shost->shost_gendev);
next prev parent reply other threads:[~2014-07-27 15:07 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-07-25 14:23 [PATCH 1/5] ARM: imx: Remove references to platform_bus in mxc code Pawel Moll
2014-07-25 14:23 ` [PATCH 2/5] char: tile-srom: Remove reference to platform_bus Pawel Moll
2014-07-31 20:24 ` Chris Metcalf
2014-07-31 21:32 ` Greg Kroah-Hartman
2014-08-01 17:21 ` Pawel Moll
2014-08-05 20:08 ` Chris Metcalf
2014-08-05 23:06 ` Greg Kroah-Hartman
2014-08-08 16:34 ` Pawel Moll
2014-08-08 16:39 ` Pawel Moll
2014-08-11 2:38 ` Chris Metcalf
2014-08-29 18:43 ` Chris Metcalf
2014-09-01 12:27 ` Pawel Moll
2014-09-01 13:53 ` Chris Metcalf
2014-07-25 14:23 ` [PATCH 3/5] mmc: sdhci-pltfm: Do not use parent as the host's device Pawel Moll
2014-08-08 16:36 ` Pawel Moll
2014-08-11 9:07 ` Ulf Hansson
2014-08-11 9:15 ` Pawel Moll
2014-08-11 9:32 ` Ulf Hansson
2014-08-12 8:58 ` Ulf Hansson
2014-08-11 10:02 ` Russell King - ARM Linux
2014-07-25 14:23 ` [PATCH 4/5] [SCSI] Do not use platform_bus as a parent Pawel Moll
2014-07-25 14:46 ` James Bottomley
2014-07-25 15:40 ` Pawel Moll
2014-07-26 20:11 ` Greg Kroah-Hartman
2014-07-27 3:52 ` James Bottomley
2014-07-27 15:07 ` Greg Kroah-Hartman [this message]
2014-08-01 17:25 ` Pawel Moll
2014-07-25 14:23 ` [PATCH 5/5] platform: Make platform_bus device a platform device Pawel Moll
2014-07-26 20:12 ` Greg Kroah-Hartman
2014-08-01 17:21 ` Pawel Moll
2014-07-26 20:13 ` Greg Kroah-Hartman
2014-08-01 17:21 ` Pawel Moll
2014-07-28 1:45 ` [PATCH 1/5] ARM: imx: Remove references to platform_bus in mxc code Shawn Guo
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