diff options
Diffstat (limited to 'drivers/usb/core/message.c')
| -rw-r--r-- | drivers/usb/core/message.c | 32 |
1 files changed, 10 insertions, 22 deletions
diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c index 9720e699f47..da718e84d58 100644 --- a/drivers/usb/core/message.c +++ b/drivers/usb/core/message.c @@ -459,35 +459,23 @@ int usb_sg_init(struct usb_sg_request *io, struct usb_device *dev, io->urbs[i]->context = io; /* - * Some systems need to revert to PIO when DMA is - * temporarily unavailable. For their sakes, both - * transfer_buffer and transfer_dma are set when - * possible. However this can only work on systems - * without: + * Some systems need to revert to PIO when DMA is temporarily + * unavailable. For their sakes, both transfer_buffer and + * transfer_dma are set when possible. * - * - HIGHMEM, since DMA buffers located in high memory - * are not directly addressable by the CPU for PIO; - * - * - IOMMU, since dma_map_sg() is allowed to use an - * IOMMU to make virtually discontiguous buffers be - * "dma-contiguous" so that PIO and DMA need diferent - * numbers of URBs. - * - * So when HIGHMEM or IOMMU are in use, transfer_buffer - * is NULL to prevent stale pointers and to help spot - * bugs. + * Note that if IOMMU coalescing occurred, we cannot + * trust sg_page anymore, so check if S/G list shrunk. */ + if (io->nents == io->entries && !PageHighMem(sg_page(sg))) + io->urbs[i]->transfer_buffer = sg_virt(sg); + else + io->urbs[i]->transfer_buffer = NULL; + if (dma) { io->urbs[i]->transfer_dma = sg_dma_address(sg); len = sg_dma_len(sg); -#if defined(CONFIG_HIGHMEM) || defined(CONFIG_GART_IOMMU) - io->urbs[i]->transfer_buffer = NULL; -#else - io->urbs[i]->transfer_buffer = sg_virt(sg); -#endif } else { /* hc may use _only_ transfer_buffer */ - io->urbs[i]->transfer_buffer = sg_virt(sg); len = sg->length; } |