| Message ID | 20200914073343.1579578-6-hch@lst.de (mailing list archive) |
|---|---|
| State | Not Applicable, archived |
| Headers | show |
| Series | [1/6] ARM/dma-mapping: remove a __arch_page_to_dma #error | expand |
On Mon, Sep 14, 2020 at 09:33:42AM +0200, Christoph Hellwig wrote: > 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 b44bbc46a8bb > ("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 21e07dba9fb1 > ("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>
diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c index 6197938dcc2d8f..9e45732dc1d1d1 100644 --- a/drivers/usb/core/message.c +++ b/drivers/usb/core/message.c @@ -1954,12 +1954,6 @@ int usb_set_configuration(struct usb_device *dev, int configuration) 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); diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c index bafc113f2b3ef3..9b4ac4415f1a47 100644 --- a/drivers/usb/core/usb.c +++ b/drivers/usb/core/usb.c @@ -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;
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 b44bbc46a8bb ("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 21e07dba9fb1 ("scsi: reduce use of block bounce buffers") years ago. Signed-off-by: Christoph Hellwig <hch@lst.de> --- drivers/usb/core/message.c | 6 ------ drivers/usb/core/usb.c | 12 ------------ 2 files changed, 18 deletions(-)