On 17-02-06 09:28:22, Greg KH wrote: > On Mon, Feb 06, 2017 at 10:14:44AM +0200, Petko Manolov wrote: > > On 17-02-05 01:30:39, Greg KH wrote: > > > On Sat, Feb 04, 2017 at 04:56:03PM +0000, Ben Hutchings wrote: > > > > Allocating USB buffers on the stack is not portable, and no longer works > > > > on x86_64 (with VMAP_STACK enabled as per default). > > > > > > It's never worked on other platforms, so these should go to the stable > > > releases please. > > > > As far as i know both drivers works fine on other platforms, though I only > > tested it on arm and mipsel. ;) > > It all depends on the arm and mips platforms, the ones that can not DMA from > stack memory are the ones that would always fail here (since the 2.2 kernel > days). Seems like most modern SOCs have decent DMA controllers. > > Random thought: isn't it better to add the alloc/free code in > > usb_control_msg() and avoid code duplication all over the driver space? > > A very long time ago we considered it, but realized that the majority of > drivers already had the memory dynamically allocated, so we just went with > this. Perhaps we could revisit that if it turns out we were wrong, and would > simplify things. A quick glance at usb_control_msg() users (looked only at .../net/usb and .../usb/serial) shows that most of them have the buffer allocated in stack. These transfers are relatively infrequent and quite small the performance hit caused by memcpy() should also be negligible. I suspect getting the buffer allocation in usb_control_msg() will help with two things in the same time: - allocate in DMA-able memory; - code reduction; On the bad side i've no idea who'll volunteer to go through all usb_control_msg() sites and perform the fix. Seems like the right job for an intern to me. :D cheers, Petko -- 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
