From mboxrd@z Thu Jan 1 00:00:00 1970 From: Tony Lindgren Subject: Re: High CPU usage when video streaming on EHCI, 3.17.8 kernel with DMA enabled Date: Wed, 1 Jul 2015 23:22:35 -0700 Message-ID: <20150702062234.GZ4156@atomide.com> References: <20150518102715.34e29c33@perruche.parrot.biz> <20150518145919.GC10274@atomide.com> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Return-path: Content-Disposition: inline In-Reply-To: Sender: linux-usb-owner-u79uwXL29TY76Z2rM5mHXA@public.gmane.org To: Tom Mises Cc: Ash Charles , Matthieu CASTET , Alan Stern , "linux-omap-u79uwXL29TY76Z2rM5mHXA@public.gmane.org" , linux-usb-u79uwXL29TY76Z2rM5mHXA@public.gmane.org, linux-uvc-devel-5NWGOfrQmneRv+LV9MX5uipxlwaOVQ5f@public.gmane.org List-Id: linux-omap@vger.kernel.org * Tom Mises [150701 11:24]: > On Mon, May 18, 2015 at 8:59 AM, Tony Lindgren wrote: > > For the memcpy part with DMA this patch should help too: > > > > [PATCH] dmaengine: omap-dma: Add support for memcpy > > The patch should help, but not out of the box as far as I understand. > My understanding is that to take advantage of this, it would be > necessary to explicitly call the DMA API either by replacing memcpy() > in uvc_video_decode_data() or by modyfying the memcpy() > implementation. Is that correct? Yes you should be able to configure the DMA to do memory-to-memory copy where both source and destination address is looping over the desired buffer size. Ideally you would move the data from camera directly to the buffer without doing a memcpy inbetween. Regards, Tony -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo-u79uwXL29TY76Z2rM5mHXA@public.gmane.org More majordomo info at http://vger.kernel.org/majordomo-info.html