Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762404Ab3DCLwr (ORCPT ); Wed, 3 Apr 2013 07:52:47 -0400 Received: from comal.ext.ti.com ([198.47.26.152]:59355 "EHLO comal.ext.ti.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1760206Ab3DCLwp (ORCPT ); Wed, 3 Apr 2013 07:52:45 -0400 Message-ID: <515C17F9.4040300@ti.com> Date: Wed, 3 Apr 2013 13:52:25 +0200 From: Peter Ujfalusi User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:17.0) Gecko/20130328 Thunderbird/17.0.4 MIME-Version: 1.0 To: Santosh Shilimkar CC: Russell King - ARM Linux , Vinod Koul , Dan Williams , Tony Lindgren , Jarkko Nikula , Felipe Balbi , , , , Peter Meerwald Subject: Re: [RFC v2] dmaengine: omap-dma: Start DMA without delay for cyclic channels References: <1364987862-14597-1-git-send-email-peter.ujfalusi@ti.com> <515C117A.6060700@ti.com> In-Reply-To: <515C117A.6060700@ti.com> Content-Type: text/plain; charset="ISO-8859-1" Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 2594 Lines: 75 On 04/03/2013 01:24 PM, Santosh Shilimkar wrote: > On Wednesday 03 April 2013 04:47 PM, Peter Ujfalusi wrote: >> cyclic DMA is only used by audio which needs DMA to be started without a >> delay. >> If the DMA for audio is started using the tasklet we experience random >> channel switch (to be more precise: channel shift). >> >> Reported-by: Peter Meerwald >> Signed-off-by: Peter Ujfalusi >> --- >> Hi Russell, >> >> Instead of removing the tasklet we can identify the DMA channel used by audio >> based on the cyclic flag of the channel. >> I think this can be used as a short term solution to fix the audio channel shift >> issue and later when we have the dynamic DMA channel allocation we can adjust >> the code. >> >> Regards, >> Peter >> >> drivers/dma/omap-dma.c | 20 ++++++++++++++------ >> 1 file changed, 14 insertions(+), 6 deletions(-) >> >> diff --git a/drivers/dma/omap-dma.c b/drivers/dma/omap-dma.c >> index 2ea3d7e..ec3fc4f 100644 >> --- a/drivers/dma/omap-dma.c >> +++ b/drivers/dma/omap-dma.c >> @@ -282,12 +282,20 @@ static void omap_dma_issue_pending(struct dma_chan *chan) >> >> spin_lock_irqsave(&c->vc.lock, flags); >> if (vchan_issue_pending(&c->vc) && !c->desc) { > If you add "!c->cyclic" in above if then you can avoid > indentation change and just have else for cyclic case. It can not be embedded there because of the existing tests. How would we handle the case when c->desc is _not_ NULL and c->cyclic is false? We would need to test again in else, but we can not do this for the vchan_issue_pending(&c->vc). > >> - struct omap_dmadev *d = to_omap_dma_dev(chan->device); >> - spin_lock(&d->lock); >> - if (list_empty(&c->node)) >> - list_add_tail(&c->node, &d->pending); >> - spin_unlock(&d->lock); >> - tasklet_schedule(&d->task); >> + /* >> + * c->cyclic is used only by audio and in this case the DMA need >> + * to be started without delay. >> + */ >> + if (!c->cyclic) { >> + struct omap_dmadev *d = to_omap_dma_dev(chan->device); >> + spin_lock(&d->lock); >> + if (list_empty(&c->node)) >> + list_add_tail(&c->node, &d->pending); >> + spin_unlock(&d->lock); >> + tasklet_schedule(&d->task); >> + } else { >> + omap_dma_start_desc(c); >> + } >> } >> spin_unlock_irqrestore(&c->vc.lock, flags); >> } >> > -- P?ter -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/