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

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Date:   Mon, 14 Sep 2020 12:28:34 +1000
From:   Nicholas Piggin <npiggin@...il.com>
To:     "broonie@...nel.org" <broonie@...nel.org>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linuxppc-dev@...ts.ozlabs.org" <linuxppc-dev@...ts.ozlabs.org>,
        "linux-spi@...r.kernel.org" <linux-spi@...r.kernel.org>,
        "stable@...r.kernel.org" <stable@...r.kernel.org>
Subject: Re: [PATCH] spi: fsl-espi: Only process interrupts for expected
 events

Excerpts from Chris Packham's message of September 14, 2020 8:03 am:
> Hi All,
> 
> On 4/09/20 12:28 pm, 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
>> ---
> ping?

I don't know the code/hardware but thanks for tracking this down.

Was there anything more to be done with Jocke's observations, or would 
that be a follow-up patch if anything?

If this patch fixes your problem it should probably go in, unless there 
are any objections.

Thanks,
Nick

>>
>> 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;
>>   	}