On Thu, Aug 03, 2017 at 12:50:20PM +0100, Robin Murphy wrote: > Hi Johan, > > On 03/08/17 11:05, Johan Hovold wrote: > > USB devices use the DMA mask and offset of the controller, which have > > already been setup when a device is probed. Note that modifying the mask > > of a USB device would change the mask for the controller (and all > > devices on the bus) as the mask is literally shared. > > If I understand the situation correctly, some USB devices have to > pretend to be DMA masters in order to interact properly with subsystems > that make DMA mapping calls directly, because those subsystems don't > have access to the 'real' DMA master sysdev (and shouldn't have to know > anyway). If that is the case, then there's really a much more general > problem, because correct DMA API operation can depend on other things > like IOMMU stuff and archdata which cannot be arbitrarily copied or > shared between devices. Right, take a look at usb_alloc_dev() and commit b44bbc46a8bb ("usb: core: setup dma_pfn_offset for USB devices and, interfaces") for some background. Note that we've been setting dma_mask this way since before git. > What with things like the DWC3 glue layer device mess as well, the > feeling I'm getting is that this probably needs addressing at the driver > core/DMA API level - if we had some flag in struct device to say "I can > effectively do DMA, but proxied through my parent", the DMA API could > pick that up and internally chase down the correct DMA master device, > and we could then probably clean up a lot of the "sysdev"-type gunk in > various driver layers as well. > > For expedience of keeping the existing hack working, though, I think > this patch is OK. Yes, we should fix the immediate regression first. > > Since commit 2bf698671205 ("USB: of: fix root-hub device-tree node > > handling"), of_dma_configure() would be called also for root hubs, which > > use the device node of the controller. A separate bug that makes > > of_dma_configure() generate a 30-bit DMA mask from the RPI3's > > "dma-ranges" would thus set a broken mask also for the controller. This > > in turn leads to USB devices failing to enumerate when control transfers > > fail: > > If we're calling out that (long-standing) bug in particular, it might be > worth clarifying that it's benign for the HCD itself because the dwc2 > driver still sets a 32-bit mask afterwards on probe - the breakage is > specifically from the subsequent of_dma_configure() call with the root > hub resetting the HCD's mask again *after* the HCD driver has configured > it (and started to perform DMA), which is just fundamentally wrong > regardless of what it ends up set to. Good point, I'll amend this paragraph. > > dwc2 3f980000.usb: Cannot do DMA to address 0x000000003a166a00 > > > > Fix this, and similar future problems, by simply skipping USB devices > > when dma_configure() is called during probe. > > > > Fixes: 09515ef5ddad ("of/acpi: Configure dma operations at probe time for platform/amba/pci bus devices") > > Cc: stable <stable@xxxxxxxxxxxxxxx> # 4.12 > > Cc: Robin Murphy <robin.murphy@xxxxxxx> > > Cc: Sricharan R <sricharan@xxxxxxxxxxxxxx> > > Cc: Stefan Wahren <stefan.wahren@xxxxxxxx> > > Reported-by: Hans Verkuil <hverkuil@xxxxxxxxx> > > Signed-off-by: Johan Hovold <johan@xxxxxxxxxx> > > --- > > drivers/base/dma-mapping.c | 8 ++++++++ > > 1 file changed, 8 insertions(+) > > > > diff --git a/drivers/base/dma-mapping.c b/drivers/base/dma-mapping.c > > index b555ff9dd8fc..c6cde7e79599 100644 > > --- a/drivers/base/dma-mapping.c > > +++ b/drivers/base/dma-mapping.c > > @@ -13,6 +13,7 @@ > > #include <linux/gfp.h> > > #include <linux/of_device.h> > > #include <linux/slab.h> > > +#include <linux/usb.h> > > #include <linux/vmalloc.h> > > > > /* > > @@ -345,6 +346,10 @@ int dma_configure(struct device *dev) > > enum dev_dma_attr attr; > > int ret = 0; > > > > + /* USB devices share the controller's mask. */ > > + if (dev->bus == &usb_bus_type) > > Maybe a dev_is_usb() helper to mimic dev_is_pci()? Yeah, I considered that but figured it wasn't essential for a minimal patch marked for stable, but then again, such a macro would be straight-forward enough. I'll respin. > > + return 0; > > + > > if (dev_is_pci(dev)) { > > bridge = pci_get_host_bridge_device(to_pci_dev(dev)); > > dma_dev = bridge; > > @@ -369,6 +374,9 @@ int dma_configure(struct device *dev) > > > > void dma_deconfigure(struct device *dev) > > { > > + if (dev->bus == &usb_bus_type) > > + return; > > + > > of_dma_deconfigure(dev); > > acpi_dma_deconfigure(dev); > > } Thanks, Johan