| Message ID | 92772fe0-5c3d-b2f0-6ab3-0504f29de7e4@ti.com |
|---|---|
| State | Accepted |
| Commit | b44bbc46a8bbcd9c6bb1d167ca3f78d3aa5ee41d |
| Headers | show |
On Tuesday, September 13, 2016 11:16:03 AM CEST Roger Quadros wrote: > If dma_pfn_offset is not inherited correctly from the host controller, > it might result in sub-optimal configuration as bounce > buffer limit might be set to less than optimal level. > > Consider the mass storage device case. > USB storage driver creates a scsi host for the mass storage interface in > drivers/usb/storage/usb.c > The scsi host parent device is nothing but the the USB interface device. > Now, __scsi_init_queue() calls scsi_calculate_bounce_limit() to find out > and set the block layer bounce limit. > scsi_calculate_bounce_limit() uses dma_max_pfn(host_dev) to get the > bounce_limit. host_dev is nothing but the device representing the > mass storage interface. > If that device doesn't have the right dma_pfn_offset, then dma_max_pfn() > is messed up and the bounce buffer limit is wrong. > > e.g. On Keystone 2 systems, dma_max_pfn() is 0x87FFFF and dma_mask_pfn > is 0xFFFFF. Consider a mass storage use case: Without this patch, > usb scsi host device (usb-storage) will get a dma_pfn_offset of 0 resulting > in a dma_max_pfn() of 0xFFFFF within the scsi layer > (scsi_calculate_bounce_limit()). > This will result in bounce buffers being unnecessarily used. > > Hint: On 32-bit ARM platforms dma_max_pfn() = dma_mask_pfn + dma_pfn_offset > > Signed-off-by: Roger Quadros <rogerq@ti.com> Acked-by: Arnd Bergmann <arnd@arndb.de>
diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c index 0406a59..bb617df 100644 --- a/drivers/usb/core/message.c +++ b/drivers/usb/core/message.c @@ -1862,7 +1862,12 @@ 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); diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c index 5e80697..5921514 100644 --- a/drivers/usb/core/usb.c +++ b/drivers/usb/core/usb.c @@ -440,7 +440,18 @@ 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->controller->dma_mask; + dev->dev.dma_pfn_offset = bus->controller->dma_pfn_offset; set_dev_node(&dev->dev, dev_to_node(bus->controller)); dev->state = USB_STATE_ATTACHED; dev->lpm_disable_count = 1;
If dma_pfn_offset is not inherited correctly from the host controller, it might result in sub-optimal configuration as bounce buffer limit might be set to less than optimal level. Consider the mass storage device case. USB storage driver creates a scsi host for the mass storage interface in drivers/usb/storage/usb.c The scsi host parent device is nothing but the the USB interface device. Now, __scsi_init_queue() calls scsi_calculate_bounce_limit() to find out and set the block layer bounce limit. scsi_calculate_bounce_limit() uses dma_max_pfn(host_dev) to get the bounce_limit. host_dev is nothing but the device representing the mass storage interface. If that device doesn't have the right dma_pfn_offset, then dma_max_pfn() is messed up and the bounce buffer limit is wrong. e.g. On Keystone 2 systems, dma_max_pfn() is 0x87FFFF and dma_mask_pfn is 0xFFFFF. Consider a mass storage use case: Without this patch, usb scsi host device (usb-storage) will get a dma_pfn_offset of 0 resulting in a dma_max_pfn() of 0xFFFFF within the scsi layer (scsi_calculate_bounce_limit()). This will result in bounce buffers being unnecessarily used. Hint: On 32-bit ARM platforms dma_max_pfn() = dma_mask_pfn + dma_pfn_offset Signed-off-by: Roger Quadros <rogerq@ti.com> --- Changelog: v4: - added comment in the code as to why we need to set dma_mask and dma_pfn_offset for usb devices. v3: - removed comments from code as commit log is sufficient. v2: - added more information in commit log and code. drivers/usb/core/message.c | 5 +++++ drivers/usb/core/usb.c | 11 +++++++++++ 2 files changed, 16 insertions(+) -- 2.7.4