From mboxrd@z Thu Jan 1 00:00:00 1970 Return-path: Received: from mx3.redhat.com (mx3.redhat.com [172.16.48.32]) by int-mx1.corp.redhat.com (8.13.1/8.13.1) with ESMTP id mADAPcBU000358 for ; Thu, 13 Nov 2008 05:25:38 -0500 Received: from oceanus.site5.com (oceanus.site5.com [67.43.13.2]) by mx3.redhat.com (8.13.8/8.13.8) with ESMTP id mADANpcT019726 for ; Thu, 13 Nov 2008 05:24:13 -0500 Message-ID: <491C002F.4070804@compulab.co.il> Date: Thu, 13 Nov 2008 12:23:43 +0200 From: Mike Rapoport MIME-Version: 1.0 To: Robert Jarzmik References: <87prl4x28e.fsf@free.fr> In-Reply-To: <87prl4x28e.fsf@free.fr> Content-Type: text/plain; charset=ISO-8859-1 Content-Transfer-Encoding: 7bit Cc: video4linux-list@redhat.com Subject: Re: pxa_camera: DMA alignment requirement List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Sender: video4linux-list-bounces@redhat.com Errors-To: video4linux-list-bounces@redhat.com List-ID: Robert Jarzmik wrote: > Hello, > > In the pxa camera driver, the 3 DMA channels used are MMU page aligned. Does > somebody remember where that constraint comes from ? > > I'm wondering because the planar YUV format generated is something like this for > a 640 * 480 image : > - Y plane => 640 * 480 bytes = 307200 (and this happens to be a multiple of > pagesize : 307200 = 4096 * 75) > - U plane => 640 * 480 / 2 bytes = 153600 (and this is not a multiple of 4096) > - padding to reach next page : 2048 bytes > - V plane => 153600 bytes > - padding to reach next page : 2048 bytes > > This means a user space library should be kernel pagesize aware to transform the > output image. I don't really understand the necessity of page aligned DMA > channels. Would someone tell me please ? As far as I remember, the buffers should be page aligned to allow overlaying of captured data. > -- > Robert > > -- > video4linux-list mailing list > Unsubscribe mailto:video4linux-list-request@redhat.com?subject=unsubscribe > https://www.redhat.com/mailman/listinfo/video4linux-list > -- Sincerely yours, Mike. -- video4linux-list mailing list Unsubscribe mailto:video4linux-list-request@redhat.com?subject=unsubscribe https://www.redhat.com/mailman/listinfo/video4linux-list