Hi Matthew, I've been trying for some time to use a rootfs (ext2) on a USB memory stick on ARM platforms but without any success. The USB HCD driver is ISP1760 which doesn't use DMA. ARM has a Harvard cache architecture and what I get is incoherency between the I and D caches. The CPU I'm using (ARM11MPCore) has PIPT caches with D-cache lines allocation on write. Basically, when user space tries to execute from a new page, it faults and the data is requested via the VFS layer, SCSI block device and USB mass storage from the ISP1760 driver. The page is then mapped into user space and update_mmu_cache() called. However, since the driver is PIO, the data copied from the USB device into RAM gets stuck in the D-cache. On the above page requesting path there is no call to flush_dcache_page() to handle D-cache maintenance (for DMA drivers, that's handled by the DMA API). Since the USB mass storage code has the information about the USB driver capabilities (DMA or PIO), it looks like the best place to call flush_dcache_page(). But I got lost in the SCSI emulation and all my attempts failed to get a working rootfs. Adding flush_dcache_page() higher up in mpage_end_io_read() solves the problem but that's not the correct fix as it has wider implications and it's not needed for DMA-capable devices. Thanks. -- Catalin -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
