On Fri, Mar 17, 2017 at 04:25:21PM -0700, Michael Zoran wrote: > On Fri, 2017-03-17 at 10:24 +0900, Greg Kroah-Hartman wrote: > > On Thu, Mar 16, 2017 at 09:08:40PM -0300, Mauro Carvalho Chehab > > wrote: > > > The dwc2 hardware doesn't like to do DMA transfers without > > > aligning data in DWORD. The driver also assumes that, even > > > when there's no DMA, at dwc2_read_packet(). > > > > > > That cause buffer overflows, preventing some drivers to work. > > > > Why aren't the drivers being fixed? This is a well-known (hopefully) > > restriction on USB data buffers, can't the uvc_driver be fixed? > > > > > In the specific case of uvc_driver, it uses an array where > > > it caches the content of video controls, passing it to the > > > USB stack via usb_control_msg(). Typical controls use 1 or 2 > > > bytes. The net result is that other values of the buffer > > > gets overriden when this function is called. > > > > Not good, it should be fixed, otherwise you are going to have to try > > to > > Silly question this being an RFC an all. > > But I wonder if this would be best to fix in the core usb subsystem > rather then making an attempt to fix each and every driver and host > controller. > > Since usb_control_msg is a wrapper that can sleep, it's safe to > allocate some memory in the case the destinate buffer isn't aligned. > Essentially have the usb core handle the copy to a temp buffer and copy > it back after the transaction is over. It's come up every-so-often to do this, an additional memory allocation/copy/free isn't that big of a deal for a normal control message, but I think what prevents this from actually being changed is that there might be devices that this would affect throughput. No one has really tried, and I don't think I've ever seen a patch to make this change. That combined with the fact that all other USB transfers have this requirement, would make this one type of transfer an oddity. thanks, greg k-h -- 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
