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@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 > 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. > 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. James -- To unsubscribe from this list: send the line "unsubscribe linux-tegra" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
