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