On 15.06.2013 10:41, Ming Lei wrote: > Cc: netdev > > On Fri, Jun 14, 2013 at 9:38 PM, Jussi Kivilinna <jussi.kivilinna@xxxxxx> wrote: >> Appearently some out-of-tree USB host drivers do not handle DMA alignment for > > Looks these host drivers have to face the fact that the transfer buffer is often > DMA non-aligned from network device drivers(in fact, the buffer is from > network protocol stack), if you run usbnet, then you will get the added warning > immediately. > Yes, getting warning immediately, but once, and blaming host driver seems ok. >> URB buffers and let core/hcd.c to do the mapping on architectures that have >> minimum DMA alignment requirements. This leads to random memory corruptions >> and crashes when using USB device drivers that use unaligned URB buffers. > > Maybe you should check the dma mapping/unmapping implementation of > the arch, non-aligned buffer should have be covered by the API easily. > > Also USB Host controller should have supported non-aligned DMA buffer. >From what I found, there was some discussion about these issues around 2010: http://lists.infradead.org/pipermail/linux-arm-kernel/2010-August/022983.html To me, it seems that non-aligned buffers cannot be easily handled by all archs at dma mapping/unmapping phase and that HCD driver should do the alignment on archs that set ARCH_DMA_MINALIGN. For example, ehci_tegra does copy unaligned transfer buffers to temporary aligned buffers before letting them to USB core. > >> >> Instead of fixing host drivers, users end up posting bug reports against >> those USB device drivers that use unaligned buffers for URB; such as with >> rtl8192cu (http://thread.gmane.org/gmane.linux.kernel.wireless.general/105631). > > Not only rtl8192cu driver, all USB network device drivers have the problem. > >> >> Patch makes this issue more visible at core level, and hopefully gives hint >> for future hcd driver implementors about this problem. > > So please find the root cause first, and don't add the noise now. I think the root cause is that host driver is letting pass non-aligned buffers to core on archs that have ARCH_DMA_MINALIGN set. The warning given just before such unaligned buffer is passed to dma_map_single, which requires ARCH_DMA_MINALIGN alignment. This seems reasonable to me. -Jussi > > > Thanks, > -- 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
