linux-kernel - Re: [PATCH 11/18] spi: qup: properly detect extra interrupts

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Date:   Wed, 14 Jun 2017 15:59:53 -0400
From:   Andy Gross <andy.gross@...aro.org>
To:     Sricharan R <sricharan@...eaurora.org>
Cc:     Varadarajan Narayanan <varada@...eaurora.org>, broonie@...nel.org,
        robh+dt@...nel.org, mark.rutland@....com, david.brown@...aro.org,
        linux-spi@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org,
        linux-soc@...r.kernel.org,
        Matthew McClintock <mmcclint@...eaurora.org>
Subject: Re: [PATCH 11/18] spi: qup: properly detect extra interrupts

On Wed, Jun 14, 2017 at 12:57:25PM +0530, Sricharan R wrote:
> Hi Varada,
> 
> On 6/14/2017 11:22 AM, Varadarajan Narayanan wrote:
> > It's possible for a SPI transaction to complete and get another
> > interrupt and have it processed on the same spi_transfer before the
> > transfer_one can set it to NULL.
> > 
> > This masks unexpected interrupts, so let's set the spi_transfer to
> > NULL in the interrupt once the transaction is done. So we can
> > properly detect these bad interrupts and print warning messages.
> > 
> > Signed-off-by: Matthew McClintock <mmcclint@...eaurora.org>
> > Signed-off-by: Varadarajan Narayanan <varada@...eaurora.org>
> > ---
> >  drivers/spi/spi-qup.c | 20 +++++++++++---------
> >  1 file changed, 11 insertions(+), 9 deletions(-)
> > 
> > diff --git a/drivers/spi/spi-qup.c b/drivers/spi/spi-qup.c
> > index bd53e82..1a2a9d9 100644
> > --- a/drivers/spi/spi-qup.c
> > +++ b/drivers/spi/spi-qup.c
> > @@ -496,13 +496,13 @@ static irqreturn_t spi_qup_qup_irq(int irq, void *dev_id)
> >  	struct spi_qup *controller = dev_id;
> >  	struct spi_transfer *xfer;
> >  	u32 opflags, qup_err, spi_err;
> > -	unsigned long flags;
> >  	int error = 0;
> > +	bool done = 0;
> >  
> > -	spin_lock_irqsave(&controller->lock, flags);
> > +	spin_lock(&controller->lock);
> >  	xfer = controller->xfer;
> >  	controller->xfer = NULL;
> > -	spin_unlock_irqrestore(&controller->lock, flags);
> > +	spin_unlock(&controller->lock);
> 
>  Why change the locking here ?
> 
> >  
> >  	qup_err = readl_relaxed(controller->base + QUP_ERROR_FLAGS);
> >  	spi_err = readl_relaxed(controller->base + SPI_ERROR_FLAGS);
> > @@ -556,16 +556,19 @@ static irqreturn_t spi_qup_qup_irq(int irq, void *dev_id)
> >  			spi_qup_write(controller, xfer);
> >  	}
> >  
> > -	spin_lock_irqsave(&controller->lock, flags);
> > -	controller->error = error;
> > -	controller->xfer = xfer;
> > -	spin_unlock_irqrestore(&controller->lock, flags);
> > -
> >  	/* re-read opflags as flags may have changed due to actions above */
> >  	opflags = readl_relaxed(controller->base + QUP_OPERATIONAL);
> >  
> >  	if ((controller->rx_bytes == xfer->len &&
> >  		(opflags & QUP_OP_MAX_INPUT_DONE_FLAG)) ||  error)
> > +		done = true;
> > +
> > +	spin_lock(&controller->lock);
> > +	controller->error = error;
> > +	controller->xfer = done ? NULL : xfer;
> > +	spin_unlock(&controller->lock);
> > +
> > +	if (done)
> >  		complete(&controller->done);
> >  
>   Its not clear, why the driver is setting the controller->xfer = NULL
>   and restoring it inside the irq. This patch seems to fix things on
>   top of that.

I think the original intent was to make sure that the irqhandler knew that there
was no outstanding transaction.  This begs the question of why that would ever
be necessary.  I think it would suffice to rework all of that to remove that
behavior and perhaps enable/disable the irq as we need to during transactions.

I've never been a fan of the controller->xfer being set to NULL.


Regards,

Andy