Hi, Alan:
Please look at the attached patch. It allows the "new" usbmon to show
the storage data in kernels that could possibly be running on systems
with GART-based IOMMUs, but aren't actually. These #ifdefs always
bothered me.
Greetings,
-- Pete
diff --git a/drivers/usb/core/message.c b/drivers/usb/core/message.c
index b626283..e2ecf36 100644
--- a/drivers/usb/core/message.c
+++ b/drivers/usb/core/message.c
@@ -421,30 +421,21 @@ int usb_sg_init(struct usb_sg_request *io, struct usb_device *dev,
/*
* 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:
+ * 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 the IOMMU coalescing occured, 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;
}
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