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SubjectRe: [PATCH -next 7/8] dmaengine: xilinx_dma: Check for both idle and halted state in axidma stop_transfer
On Fri, Sep 27, 2019 at 06:48:29AM +0000, Radhey Shyam Pandey wrote:
> > -----Original Message-----
> > From: Vinod Koul <vkoul@kernel.org>
> > Sent: Thursday, September 26, 2019 10:51 PM
> > To: Radhey Shyam Pandey <radheys@xilinx.com>
> > Cc: dan.j.williams@intel.com; Michal Simek <michals@xilinx.com>;
> > nick.graumann@gmail.com; andrea.merello@gmail.com; Appana Durga
> > Kedareswara Rao <appanad@xilinx.com>; mcgrof@kernel.org;
> > dmaengine@vger.kernel.org; linux-kernel@vger.kernel.org
> > Subject: Re: [PATCH -next 7/8] dmaengine: xilinx_dma: Check for both idle
> > and halted state in axidma stop_transfer
> >
> > On 05-09-19, 22:07, Radhey Shyam Pandey wrote:
> > > From: Nicholas Graumann <nick.graumann@gmail.com>
> > >
> > > When polling for a stopped transfer in AXI DMA mode, in some cases the
> > > status of the channel may indicate IDLE instead of HALTED if the
> > > channel was reset due to an error.
> > >
> > > Signed-off-by: Nicholas Graumann <nick.graumann@gmail.com>
> > > Signed-off-by: Radhey Shyam Pandey
> > <radhey.shyam.pandey@xilinx.com>
> > > ---
> > > drivers/dma/xilinx/xilinx_dma.c | 5 +++--
> > > 1 file changed, 3 insertions(+), 2 deletions(-)
> > >
> > > diff --git a/drivers/dma/xilinx/xilinx_dma.c
> > b/drivers/dma/xilinx/xilinx_dma.c
> > > index b5dd62a..0896e07 100644
> > > --- a/drivers/dma/xilinx/xilinx_dma.c
> > > +++ b/drivers/dma/xilinx/xilinx_dma.c
> > > @@ -1092,8 +1092,9 @@ static int xilinx_dma_stop_transfer(struct
> > xilinx_dma_chan *chan)
> > >
> > > /* Wait for the hardware to halt */
> > > return xilinx_dma_poll_timeout(chan, XILINX_DMA_REG_DMASR,
> > val,
> > > - val & XILINX_DMA_DMASR_HALTED, 0,
> > > - XILINX_DMA_LOOP_COUNT);
> > > + val | (XILINX_DMA_DMASR_IDLE |
> > > + XILINX_DMA_DMASR_HALTED),
> >
> > The condition was bitwise AND and now is OR.. ??
>
> Ah, it should be same as before . Only _IDLE mask should be in OR.
>
> Also on second thought to this patch- we need to describe which error
> scenario "in some cases the status of the channel may indicate IDLE
> instead of HALTED" as mentioned in commit description.
>
> @Nick: Can you comment?
>
In regard to the mask question, yes, this looks like a bug.
We should be AND'ing with the mask like before.

As far as the state, usually when we saw the IDLE state when invoking
dmaengine_terminate_all on a channel that had errors. I have not
proved this, but I believe what happened was the following:

New transactions were queued when chan->err was set, causing
xilinx_dma_chan_reset to be invoked which ultimately results in the
hardware being in an IDLE state by the time xilinx_dma_terminate_all
gets around to invoking stop_transfer. At that point, stop_transfer is
going to time out waiting for the hardware to indicate it has HALTED and
ultimately will time out.


In any case, xilinx_dma_stop_transfer should be fine with the hardware
being in an IDLE state to indicate that the active transfer is stopped.
Case in point: The CDMA core also covered by this driver only has an
IDLE bit and no HALTED bit in its DMASR, and it checks for just the IDLE
bit in xilinx_cdma_stop_transfer().
> >
> > > + 0, XILINX_DMA_LOOP_COUNT);
> > > }
> > >
> > > /**
> > > --
> > > 2.7.4
> >
> > --
> > ~Vinod

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