return -ENOMEM;
offset = (void *)&desc->buffer - (void *)desc;
- desc->buffer_size = PAGE_SIZE - offset;
+ /*
+ * Some controllers, like JMicron ones, always issue 0x20-byte DMA reads
+ * for descriptors, even 0x10-byte ones. This can cause page faults when
+ * an IOMMU is in use and the oversized read crosses a page boundary.
+ * Work around this by always leaving at least 0x10 bytes of padding.
+ */
+ desc->buffer_size = PAGE_SIZE - offset - 0x10;
desc->buffer_bus = bus_addr + offset;
desc->used = 0;