linux-kernel - RE: [PATCH] dmaengine: xilinx_dma: Reset DMA channel in dma_terminate

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Date:   Wed, 11 Dec 2019 14:46:06 +0000
From:   Radhey Shyam Pandey <radheys@...inx.com>
To:     Vinod Koul <vkoul@...nel.org>
CC:     "dan.j.williams@...el.com" <dan.j.williams@...el.com>,
        Michal Simek <michals@...inx.com>,
        "nick.graumann@...il.com" <nick.graumann@...il.com>,
        "andrea.merello@...il.com" <andrea.merello@...il.com>,
        Appana Durga Kedareswara Rao <appanad@...inx.com>,
        "mcgrof@...nel.org" <mcgrof@...nel.org>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        git <git@...inx.com>
Subject: RE: [PATCH] dmaengine: xilinx_dma: Reset DMA channel in
 dma_terminate_all

> -----Original Message-----
> From: Vinod Koul <vkoul@...nel.org>
> Sent: Tuesday, December 10, 2019 11:31 AM
> To: Radhey Shyam Pandey <radheys@...inx.com>
> Cc: dan.j.williams@...el.com; Michal Simek <michals@...inx.com>;
> nick.graumann@...il.com; andrea.merello@...il.com; Appana Durga
> Kedareswara Rao <appanad@...inx.com>; mcgrof@...nel.org;
> dmaengine@...r.kernel.org; linux-kernel@...r.kernel.org; git
> <git@...inx.com>
> Subject: Re: [PATCH] dmaengine: xilinx_dma: Reset DMA channel in
> dma_terminate_all
> 
> On 25-11-19, 12:12, Radhey Shyam Pandey wrote:
> > Reset DMA channel after stop to ensure that pending transfers and
> > FIFOs in the datapath are flushed or completed. It fixes intermittent
> > data verification failure reported by xilinx dma test client.
> >
> > Signed-off-by: Radhey Shyam Pandey <radhey.shyam.pandey@...inx.com>
> > ---
> >  drivers/dma/xilinx/xilinx_dma.c | 17 +++++++++--------
> >  1 file changed, 9 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/dma/xilinx/xilinx_dma.c
> > b/drivers/dma/xilinx/xilinx_dma.c index a9c5d5c..6f1539c 100644
> > --- a/drivers/dma/xilinx/xilinx_dma.c
> > +++ b/drivers/dma/xilinx/xilinx_dma.c
> > @@ -2404,16 +2404,17 @@ static int xilinx_dma_terminate_all(struct
> dma_chan *dchan)
> >  	u32 reg;
> >  	int err;
> >
> > -	if (chan->cyclic)
> > -		xilinx_dma_chan_reset(chan);
> 
> So reset is required for non cyclic cases as well now?

Yes. In absence of reset in non-cyclic case, when dmatest client
driver is stressed and loaded/unloaded multiple times we see dma 
data comparison failures. Possibly IP is prefetching/holding the
previous state and reset ensures a clean state on each iteration.
> 
> > -
> > -	err = chan->stop_transfer(chan);
> > -	if (err) {
> > -		dev_err(chan->dev, "Cannot stop channel %p: %x\n",
> > -			chan, dma_ctrl_read(chan,
> XILINX_DMA_REG_DMASR));
> > -		chan->err = true;
> > +	if (!chan->cyclic) {
> > +		err = chan->stop_transfer(chan);
> 
> no stop for cyclic now..?
After reset stop is not needed, so for the cyclic mode we only do reset.

> 
> > +		if (err) {
> > +			dev_err(chan->dev, "Cannot stop channel %p: %x\n",
> > +				chan, dma_ctrl_read(chan,
> > +				XILINX_DMA_REG_DMASR));
> > +			chan->err = true;
> > +		}
> >  	}
> >
> > +	xilinx_dma_chan_reset(chan);
> >  	/* Remove and free all of the descriptors in the lists */
> >  	xilinx_dma_free_descriptors(chan);
> >  	chan->idle = true;
> > --
> > 2.7.4
> 
> --
> ~Vinod