• Roger Quadros's avatar
    usb: core: setup dma_pfn_offset for USB devices and, interfaces · b44bbc46
    Roger Quadros authored
    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: default avatarRoger Quadros <rogerq@ti.com>
    Acked-by: default avatarArnd Bergmann <arnd@arndb.de>
    Acked-by: default avatarAlan Stern <stern@rowland.harvard.edu>
    Signed-off-by: default avatarGreg Kroah-Hartman <gregkh@linuxfoundation.org>
    b44bbc46
usb.c 31.9 KB