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

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Date:   Wed, 18 Dec 2019 13:22:34 +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: Wednesday, December 18, 2019 11:35 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 11-12-19, 14:46, Radhey Shyam Pandey wrote:
> > > -----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.
> 
> Okay makes sense, can you please add these as comments, down the line
> these will be very useful for you & others to debug!

Thanks for the review. I agree, will include the comments in v2.
> 
> --
> ~Vinod