linux-kernel - Re: [PATCH 07/18] spi: qup: Fix transaction done signaling

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Message-ID: <83e60e35-747f-4427-b77c-5dda653432ae@codeaurora.org>
Date:   Thu, 15 Jun 2017 10:44:43 +0530
From:   Sricharan R <sricharan@...eaurora.org>
To:     Andy Gross <andy.gross@...aro.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
Subject: Re: [PATCH 07/18] spi: qup: Fix transaction done signaling

Hi Andy,

On 6/15/2017 1:21 AM, Andy Gross wrote:
> On Wed, Jun 14, 2017 at 12:43:43PM +0530, Sricharan R wrote:
>> Hi Varada,
>>
>> On 6/14/2017 11:22 AM, Varadarajan Narayanan wrote:
>>> Wait to signal done until we get all of the interrupts we are expecting
>>> to get for a transaction.  If we don't wait for the input done flag, we
>>> can be inbetween transactions when the done flag comes in and this can
>>> mess up the next transaction.
>>>
>>> Signed-off-by: Andy Gross <andy.gross@...aro.org>
>>> Signed-off-by: Varadarajan Narayanan <varada@...eaurora.org>
>>> ---
>>>  drivers/spi/spi-qup.c | 3 ++-
>>>  1 file changed, 2 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/spi/spi-qup.c b/drivers/spi/spi-qup.c
>>> index 2124815..7c22ee4 100644
>>> --- a/drivers/spi/spi-qup.c
>>> +++ b/drivers/spi/spi-qup.c
>>> @@ -465,7 +465,8 @@ static irqreturn_t spi_qup_qup_irq(int irq, void *dev_id)
>>>  	controller->xfer = xfer;
>>>  	spin_unlock_irqrestore(&controller->lock, flags);
>>>  
>>> -	if (controller->rx_bytes == xfer->len || error)
>>> +	if ((controller->rx_bytes == xfer->len &&
>>> +		(opflags & QUP_OP_MAX_INPUT_DONE_FLAG)) ||  error)
>>
>>  Not sure why we need this additional check, because having read all the
>>  bytes implies transfer complete (or) why not just check only for
>>  QUP_OP_MAX_INPUT_DONE_FLAG ?
> 
> So you can receive an interrupt for the last data without it having also
> signalled the INPUT_DONE.  That means you'd have one more IRQ come in and if you
> don't wait for that, you could start up the next transaction and have an irq
> come in that screws up that transaction.
> 
> It might be sufficient to just wait for the INPUT_DONE_FLAG.  That cannot be
> signalled unless the rx_bytes == xfer->len.
> 

 Right, that should simply it little bit.

Regards,
 Sricharan

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