linux-kernel - Re: [PATCH] spi: fsl-espi: Only process interrupts for expected events

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Message-ID: <baac170f-4729-0519-2dca-fd8e90eba5fb@alliedtelesis.co.nz>
Date:   Wed, 23 Sep 2020 21:01:18 +0000
From:   Chris Packham <Chris.Packham@...iedtelesis.co.nz>
To:     Heiner Kallweit <hkallweit1@...il.com>,
        "broonie@...nel.org" <broonie@...nel.org>,
        "npiggin@...il.com" <npiggin@...il.com>
CC:     "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] spi: fsl-espi: Only process interrupts for expected
 events


On 24/09/20 8:27 am, Heiner Kallweit wrote:
> On 04.09.2020 02:28, Chris Packham wrote:
>> The SPIE register contains counts for the TX FIFO so any time the irq
>> handler was invoked we would attempt to process the RX/TX fifos. Use the
>> SPIM value to mask the events so that we only process interrupts that
>> were expected.
>>
>> This was a latent issue exposed by commit 3282a3da25bd ("powerpc/64:
>> Implement soft interrupt replay in C").
>>
>> Signed-off-by: Chris Packham <chris.packham@...iedtelesis.co.nz>
>> Cc: stable@...r.kernel.org
>> ---
>>
>> Notes:
>>      I've tested this on a T2080RDB and a custom board using the T2081 SoC. With
>>      this change I don't see any spurious instances of the "Transfer done but
>>      SPIE_DON isn't set!" or "Transfer done but rx/tx fifo's aren't empty!" messages
>>      and the updates to spi flash are successful.
>>      
>>      I think this should go into the stable trees that contain 3282a3da25bd but I
>>      haven't added a Fixes: tag because I think 3282a3da25bd exposed the issue as
>>      opposed to causing it.
>>
>>   drivers/spi/spi-fsl-espi.c | 5 +++--
>>   1 file changed, 3 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/spi/spi-fsl-espi.c b/drivers/spi/spi-fsl-espi.c
>> index 7e7c92cafdbb..cb120b68c0e2 100644
>> --- a/drivers/spi/spi-fsl-espi.c
>> +++ b/drivers/spi/spi-fsl-espi.c
>> @@ -574,13 +574,14 @@ static void fsl_espi_cpu_irq(struct fsl_espi *espi, u32 events)
>>   static irqreturn_t fsl_espi_irq(s32 irq, void *context_data)
>>   {
>>   	struct fsl_espi *espi = context_data;
>> -	u32 events;
>> +	u32 events, mask;
>>   
>>   	spin_lock(&espi->lock);
>>   
>>   	/* Get interrupt events(tx/rx) */
>>   	events = fsl_espi_read_reg(espi, ESPI_SPIE);
>> -	if (!events) {
>> +	mask = fsl_espi_read_reg(espi, ESPI_SPIM);
>> +	if (!(events & mask)) {
>>   		spin_unlock(&espi->lock);
>>   		return IRQ_NONE;
> Sorry, I was on vacation and therefore couldn't comment earlier.
> I'm fine with the change, just one thing could be improved IMO.
> If we skip an unneeded interrupt now, then returning IRQ_NONE
> causes reporting this interrupt as spurious. This isn't too nice
> as spurious interrupts typically are seen as a problem indicator.
> Therefore returning IRQ_HANDLED should be more appropriate.
> This would just require a comment in the code explaining why we
> do this, and why it can happen that we receive interrupts
> we're not interested in.
I'd be happy to send a follow-up to change IRQ_NONE to IRQ_HANDLED. I 
don't think the old code could have ever hit the IRQ_NONE (because event 
will always be non-zero) so it won't really be a change in behaviour. 
With the patch (that is now in spi/for-next) so far I do see a low 
number of spurious interrupts on the test setup where previously I would 
have seen failure to talk to the spi-flash.