diff options
| -rw-r--r-- | drivers/usb/core/message.c | 16 |
1 files changed, 15 insertions, 1 deletions
diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c index da4ee07e0094..b7434787db5f 100644 --- a/drivers/usb/core/message.c +++ b/drivers/usb/core/message.c @@ -412,10 +412,24 @@ int usb_sg_init ( io->urbs [i]->status = -EINPROGRESS; io->urbs [i]->actual_length = 0; + /* + * 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 HIGHMEM, since DMA buffers located + * in high memory are not directly addressable by the CPU for + * PIO ... so when HIGHMEM is in use, transfer_buffer is NULL + * to prevent stale pointers and to help spot bugs. + */ if (dma) { - /* hc may use _only_ transfer_dma */ io->urbs [i]->transfer_dma = sg_dma_address (sg + i); len = sg_dma_len (sg + i); +#ifdef CONFIG_HIGHMEM + io->urbs[i]->transfer_buffer = NULL; +#else + io->urbs[i]->transfer_buffer = + page_address(sg[i].page) + sg[i].offset; +#endif } else { /* hc may use _only_ transfer_buffer */ io->urbs [i]->transfer_buffer = |