usb: don't inherity DMA properties for USB devices (6eb0233e) · Commits · 戴 / test

As the comment in usb_alloc_dev correctly states, drivers can't use the DMA API on usb device, and at least calling dma_set_mask on them is highly dangerous. Unlike what the comment states upper level drivers also can't really use the presence of a dma mask to check for DMA support, as the dma_mask is set by default for most busses. Setting the dma_mask comes from "[PATCH] usbcore dma updates (and doc)" in BitKeeper times, as it seems like it was primarily for setting the NETIF_F_HIGHDMA flag in USB drivers, something that has long been fixed up since. Setting the dma_pfn_offset comes from commit ("usb: core: setup dma_pfn_offset for USB devices and, interfaces"), which worked around the fact that the scsi_calculate_bounce_limits functions wasn't going through the proper driver interface to query DMA information, but that function was removed in commit ("scsi: reduce use of block bounce buffers") years ago. Signed-off-by:

Christoph Hellwig <hch@lst.de> Reviewed-by:

Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/core/message.c

+0 −6

Original line number	Diff line number	Diff line
		@@ -1954,12 +1954,6 @@ free_interfaces:
		intf->dev.bus = &usb_bus_type;
		intf->dev.type = &usb_if_device_type;
		intf->dev.groups = usb_interface_groups;
		/*
		* Please refer to usb_alloc_dev() to see why we set
		* dma_mask and dma_pfn_offset.
		*/
		intf->dev.dma_mask = dev->dev.dma_mask;
		intf->dev.dma_pfn_offset = dev->dev.dma_pfn_offset;
		INIT_WORK(&intf->reset_ws, __usb_queue_reset_device);
		intf->minor = -1;
		device_initialize(&intf->dev);

drivers/usb/core/usb.c

+0 −12

Original line number	Diff line number	Diff line
		@@ -599,18 +599,6 @@ struct usb_device usb_alloc_dev(struct usb_device parent,
		dev->dev.bus = &usb_bus_type;
		dev->dev.type = &usb_device_type;
		dev->dev.groups = usb_device_groups;
		/*
		* Fake a dma_mask/offset for the USB device:
		* We cannot really use the dma-mapping API (dma_alloc_* and
		* dma_map_*) for USB devices but instead need to use
		* usb_alloc_coherent and pass data in 'urb's, but some subsystems
		* manually look into the mask/offset pair to determine whether
		* they need bounce buffers.
		* Note: calling dma_set_mask() on a USB device would set the
		* mask for the entire HCD, so don't do that.
		*/
		dev->dev.dma_mask = bus->sysdev->dma_mask;
		dev->dev.dma_pfn_offset = bus->sysdev->dma_pfn_offset;
		set_dev_node(&dev->dev, dev_to_node(bus->sysdev));
		dev->state = USB_STATE_ATTACHED;
		dev->lpm_disable_count = 1;

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