From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932287Ab3CUNPo (ORCPT ); Thu, 21 Mar 2013 09:15:44 -0400 Received: from mga01.intel.com ([192.55.52.88]:55233 "EHLO mga01.intel.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755793Ab3CUNPn (ORCPT ); Thu, 21 Mar 2013 09:15:43 -0400 X-ExtLoop1: 1 X-IronPort-AV: E=Sophos;i="4.84,886,1355126400"; d="scan'208";a="309969376" Date: Thu, 21 Mar 2013 18:20:40 +0530 From: Vinod Koul To: Andy Shevchenko Cc: Viresh Kumar , linux-kernel@vger.kernel.org Subject: Re: [PATCH] dw_dmac: don't wait for FIFO_EMPTY endlessly in dwc_chan_pause Message-ID: <20130321125040.GS10326@intel.com> References: <1363859357-31545-1-git-send-email-andriy.shevchenko@linux.intel.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1363859357-31545-1-git-send-email-andriy.shevchenko@linux.intel.com> User-Agent: Mutt/1.5.20 (2009-06-14) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Thu, Mar 21, 2013 at 11:49:17AM +0200, Andy Shevchenko wrote: > When we pause the channel after transfer is completed we might stuck in the > dwc_chan_pause() because the FIFO_EMPTY flag will never be asserted. To avoid > the endless loop we introduce a timeout here (*). The proper solution is to > somehow get the residue in FIFO and avoid busyloop when transfer is done, but > this task is not simple and fast. > > Unfortunately we can't use cpu_relax() in conjunction with jiffies checker, due > to we have interrupts disabled by spin_lock_irqsave() and there is a big chance > that no interrupts will come to update the jiffies.. > > (*) The worst case is > AHB write * FIFO size / hclk = 5.12 us, > where > AHB write = 2 cycles, > hclk = 100 MHz, > burst size = 1 byte, > FIFO size = 256 bytes. > The proposed 40us timeout might be considered as a big one, though we enter > to that state only when we have the transfer already completed. > > Signed-off-by: Andy Shevchenko Applied Thanks > --- > drivers/dma/dw_dmac.c | 5 +++-- > 1 file changed, 3 insertions(+), 2 deletions(-) > > diff --git a/drivers/dma/dw_dmac.c b/drivers/dma/dw_dmac.c > index 43a5329..43e2e89 100644 > --- a/drivers/dma/dw_dmac.c > +++ b/drivers/dma/dw_dmac.c > @@ -1030,10 +1030,11 @@ set_runtime_config(struct dma_chan *chan, struct dma_slave_config *sconfig) > static inline void dwc_chan_pause(struct dw_dma_chan *dwc) > { > u32 cfglo = channel_readl(dwc, CFG_LO); > + unsigned int count = 20; /* timeout iterations */ > > channel_writel(dwc, CFG_LO, cfglo | DWC_CFGL_CH_SUSP); > - while (!(channel_readl(dwc, CFG_LO) & DWC_CFGL_FIFO_EMPTY)) > - cpu_relax(); > + while (!(channel_readl(dwc, CFG_LO) & DWC_CFGL_FIFO_EMPTY) && count--) > + udelay(2); > > dwc->paused = true; > } > -- > 1.8.2.rc0.22.gb3600c3 >