linux-kernel - RE: [PATCH 3/3] dmaengine: ioat: adding missed issue

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Date:   Wed, 22 Apr 2020 16:45:18 +0000
From:   "Ravich, Leonid" <Leonid.Ravich@...l.com>
To:     Dave Jiang <dave.jiang@...el.com>,
        "dmaengine@...r.kernel.org" <dmaengine@...r.kernel.org>
CC:     "lravich@...il.com" <lravich@...il.com>,
        Dan Williams <dan.j.williams@...el.com>,
        Vinod Koul <vkoul@...nel.org>,
        Allison Randal <allison@...utok.net>,
        Alexios Zavras <alexios.zavras@...el.com>,
        Thomas Gleixner <tglx@...utronix.de>,
        "Barabash, Alexander" <Alexander.Barabash@...l.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 3/3] dmaengine: ioat: adding missed issue_pending to
 timeout handler

> From: Dave Jiang <dave.jiang@...el.com>
> 
> On 4/22/2020 4:22 AM, leonid.ravich@...l.com wrote:
> > From: Leonid Ravich <Leonid.Ravich@....com>
> >
> > completion timeout might trigger unnesesery DMA engine hw reboot in
> > case of missed issue_pending() .
> 
> Just curious, are you hitting a use case where this is happening? And what's
> causing the completion timeout?

Unfortunately I did  ,
in my case I missed calling  dma_async_issue_pending() after few dmaengine_prep_dma_memcpy() due to some error handling bug ,  timeout timer  were still armed due to previous requests (probably)  and when finally the timer fired the engine were active (ioat_ring_active()) so it went to reset .

At least this is the theory :).
> 
> >
> > Signed-off-by: Leonid Ravich <Leonid.Ravich@....com>
> > ---
> >   drivers/dma/ioat/dma.c | 7 +++++++
> >   1 file changed, 7 insertions(+)
> >
> > diff --git a/drivers/dma/ioat/dma.c b/drivers/dma/ioat/dma.c index
> > 55a8cf1..2ab07a3 100644
> > --- a/drivers/dma/ioat/dma.c
> > +++ b/drivers/dma/ioat/dma.c
> > @@ -955,6 +955,13 @@ void ioat_timer_event(struct timer_list *t)
> >   		goto unlock_out;
> >   	}
> >
> > +	/* handle missed issue pending case */
> > +	if (ioat_ring_pending(ioat_chan)) {
> > +		spin_lock_bh(&ioat_chan->prep_lock);
> > +		__ioat_issue_pending(ioat_chan);
> > +		spin_unlock_bh(&ioat_chan->prep_lock);
> > +	}
> > +
> >   	set_bit(IOAT_COMPLETION_ACK, &ioat_chan->state);
> >   	mod_timer(&ioat_chan->timer, jiffies + COMPLETION_TIMEOUT);
> >   unlock_out:
> >