2009/4/21 Laurent Pinchart <laurent.pinchart@xxxxxxxxx>: > On Saturday 18 April 2009 06:51:11 leiming wrote: >> On Fri, 17 Apr 2009 19:55:29 -0700 (PDT) >> >> Linus Torvalds <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote: >> > > @@ -742,7 +742,7 @@ static int uvc_alloc_urb_buffers(struct >> > > uvc_video_device *video, >> > > /* Buffers are already allocated, bail out. */ >> > > if (video->urb_size) >> > > - return 0; >> > > + return DIV_ROUND_UP(video->urb_size, psize); >> > >> > I don't think this is right. It should round _down_. >> > >> > It's supposed to return 'npackets', but if you pass it a different >> > packet size than it was passed originally, it can now return a >> > potentially bigger number than the already allocated buffer, no? >> > >> > So I think it should round down (ie use a regular divide). No? >> >> Yes,you are correct, please ignore my last reply, and following is >> the fixed patch. > > psize and video->urb_size shouldn't have changed before and after resume, > otherwise we'll get into trouble anyway. A regular divide and a round-up > divide should then return the same result. I'll take the regular divide, as it > will be more efficient. Yes. > >> Thanks. >> >> From a3b3d72cdd57a0699fb643b41b78eb7beb211ff5 Mon Sep 17 00:00:00 2001 >> From: Ming Lei <tom.leiming@xxxxxxxxx> >> Date: Wed, 15 Apr 2009 22:32:51 +0800 >> Subject: [PATCH] V4L/DVB:usbvideo:fix uvc resume failed(v2) >> >> Now urb buffers is not freed before suspend, so uvc_alloc_urb_buffers >> should return packet counts allocated originally during uvc resume >> , instead of zero. >> >> This version uses round down to return packet counts on Linus's >> suggestions, or else may lead to buffer destructed if packet size >> is changed before calling uvc_alloc_urb_buffers() in this kind of >> case. > > The comment is misleading. If the packet size changes we need to reallocate > the buffers anyway. Have you checked if the packet size (which depends on the > endpoint being selected) can be changed between suspend and resume, either by > the uvcvideo driver (I don't think it can) or the USB core ? The packet size does not change between suspend and resume. I mean uvc_alloc_urb_buffers() still can be used in other cases if buffers was not freed and is reuesed in future. It seems there is no such cases in uvcvideo now, but uvc_alloc_urb_buffers() really __can__ work in such case, isn't it? IMHO It is only used to allocate or reserve UVC_URBS usb buffers, which size is video->urb_size, and npackets can be shortened or enlarged if psize is changed, after all. Thanks! -- Lei Ming -- To unsubscribe from this list: send the line "unsubscribe linux-scsi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
