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| author | Roger Quadros <rogerq@ti.com> | 2016-09-13 11:16:03 +0300 |
|---|---|---|
| committer | Greg Kroah-Hartman <gregkh@linuxfoundation.org> | 2016-09-13 17:25:35 +0200 |
| commit | b44bbc46a8bbcd9c6bb1d167ca3f78d3aa5ee41d (patch) | |
| tree | 9aaf9cc2763417f3a79527a9422bc93648b3cbec /drivers/usb/core/usb.c | |
| parent | 9cdd8e11c2a2f4b7553823240dc16a35ffa243e9 (diff) | |
| download | linux-b44bbc46a8bbcd9c6bb1d167ca3f78d3aa5ee41d.tar.bz2 | |
usb: core: setup dma_pfn_offset for USB devices and, interfaces
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>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>
Diffstat (limited to 'drivers/usb/core/usb.c')
| -rw-r--r-- | drivers/usb/core/usb.c | 11 |
1 files changed, 11 insertions, 0 deletions
diff --git a/drivers/usb/core/usb.c b/drivers/usb/core/usb.c index 5e80697ef952..592151461017 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; |