From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1755327Ab0LIOu6 (ORCPT ); Thu, 9 Dec 2010 09:50:58 -0500 Received: from metis.ext.pengutronix.de ([92.198.50.35]:53835 "EHLO metis.ext.pengutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751897Ab0LIOu4 (ORCPT ); Thu, 9 Dec 2010 09:50:56 -0500 Date: Thu, 9 Dec 2010 15:50:51 +0100 From: Sascha Hauer To: Dan Williams Cc: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Subject: Re: [PATCH 2/2] dmaengine i.MX SDMA: protect channel0 Message-ID: <20101209145051.GO6017@pengutronix.de> References: <1291630198-9690-1-git-send-email-s.hauer@pengutronix.de> <1291630198-9690-3-git-send-email-s.hauer@pengutronix.de> MIME-Version: 1.0 Content-Type: text/plain; charset=iso-8859-15 Content-Disposition: inline Content-Transfer-Encoding: 8bit In-Reply-To: X-Sent-From: Pengutronix Hildesheim X-URL: http://www.pengutronix.de/ X-IRC: #ptxdist @freenode X-Accept-Language: de,en X-Accept-Content-Type: text/plain X-Uptime: 14:54:22 up 159 days, 5:05, 50 users, load average: 0.16, 0.15, 0.17 User-Agent: Mutt/1.5.18 (2008-05-17) X-SA-Exim-Connect-IP: 2001:6f8:1178:2:215:17ff:fe12:23b0 X-SA-Exim-Mail-From: sha@pengutronix.de X-SA-Exim-Scanned: No (on metis.ext.pengutronix.de); SAEximRunCond expanded to false X-PTX-Original-Recipient: linux-kernel@vger.kernel.org Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Tue, Dec 07, 2010 at 03:50:33PM -0800, Dan Williams wrote: > On Mon, Dec 6, 2010 at 2:09 AM, Sascha Hauer wrote: > > Channel 0 of the SDMA engine is a shared resource used by the > > other channels, thus we have to protect it with a mutex. > > > > Signed-off-by: Sascha Hauer > > --- > > This one is not making sense to me... > > >  drivers/dma/imx-sdma.c |   11 +++++++++++ > >  1 files changed, 11 insertions(+), 0 deletions(-) > > > > diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c > > index 01c4a5f..b1f5947 100644 > > --- a/drivers/dma/imx-sdma.c > > +++ b/drivers/dma/imx-sdma.c > > @@ -355,6 +355,7 @@ struct sdma_engine { > >        struct dma_device               dma_device; > >        struct clk                      *clk; > >        struct sdma_script_start_addrs  *script_addrs; > > +       struct mutex                    channel0_mutex; > >  }; > > > >  #define SDMA_H_CONFIG_DSPDMA   (1 << 12) /* indicates if the DSPDMA is used */ > > @@ -437,6 +438,8 @@ static int sdma_load_script(struct sdma_engine *sdma, void *buf, int size, > >        if (!buf_virt) > >                return -ENOMEM; > > > > +       mutex_lock(&sdma->channel0_mutex); > > + > >        bd0->mode.command = C0_SETPM; > >        bd0->mode.status = BD_DONE | BD_INTR | BD_WRAP | BD_EXTD; > >        bd0->mode.count = size / 2; > > @@ -447,6 +450,8 @@ static int sdma_load_script(struct sdma_engine *sdma, void *buf, int size, > > > >        ret = sdma_run_channel(&sdma->channel[0]); > > > > +       mutex_unlock(&sdma->channel0_mutex); > > + > > In sdma_load_script() what data structure are we protecting at single > threaded init time prior to registering channels? At the moment the lock in sdma_load_script is not needed, but I have a patch in the queue using request_firmware_nowait instead of request_firmware, so the firmware might come in after initialization (The SDMA does not really depend on the firmware, it can just offer more features when it is available) > > >        dma_free_coherent(NULL, size, buf_virt, buf_phys); > > > >        return ret; > > > @@ -684,6 +689,8 @@ static int sdma_load_context(struct sdma_channel *sdmac) > >        context->gReg[6] = sdmac->shp_addr; > >        context->gReg[7] = sdmac->watermark_level; > > > > +       mutex_lock(&sdma->channel0_mutex); > > + > >        bd0->mode.command = C0_SETDM; > >        bd0->mode.status = BD_DONE | BD_INTR | BD_WRAP | BD_EXTD; > >        bd0->mode.count = sizeof(*context) / 4; > > @@ -692,6 +699,8 @@ static int sdma_load_context(struct sdma_channel *sdmac) > > > >        ret = sdma_run_channel(&sdma->channel[0]); > > > > +       mutex_unlock(&sdma->channel0_mutex); > > + > > This sdma_load_context() is called from various ->prep() contexts. > What guarantees are there that we can sleep in these contexts? At > least ->prep_memcpy() might be called in a atomic context. I have > been assuming the same for all prep routines across archs. Currently it is only called from non interrupt context. Fact is that we need some kind of locking because channel 0 is used by the other channels. I just made a check and it shows running channel 0 only takes about 6us, so a spinlock might be a better weapon here. So forget this patch for now and I'll send an updated one using a spinlock (and no completion interrupt for channel 0). Sascha -- Pengutronix e.K. | | Industrial Linux Solutions | http://www.pengutronix.de/ | Peiner Str. 6-8, 31137 Hildesheim, Germany | Phone: +49-5121-206917-0 | Amtsgericht Hildesheim, HRA 2686 | Fax: +49-5121-206917-5555 |