linux-kernel - Re: [PATCH 1/2] spi: pxa2xx: Prepare for edge-triggered interrupts

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Date:   Mon, 16 Jan 2017 12:18:10 +0100
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        linux-arm-kernel@...ts.infradead.org
Cc:     Daniel Mack <daniel@...que.org>,
        Haojian Zhuang <haojian.zhuang@...il.com>,
        Robert Jarzmik <robert.jarzmik@...e.fr>,
        linux-kernel@...r.kernel.org,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Jarkko Nikula <jarkko.nikula@...mer.com>,
        Sascha Weisenberger <sascha.weisenberger@...mens.com>
Subject: Re: [PATCH 1/2] spi: pxa2xx: Prepare for edge-triggered interrupts

On 2017-01-16 10:24, Andy Shevchenko wrote:
> On Mon, 2017-01-16 at 10:05 +0100, Jan Kiszka wrote:
>> When using the a device with edge-triggered interrupts, such as MSIs,
>> the interrupt handler has to ensure that there is a point in time
>> during
>> its execution where all interrupts sources are silent so that a new
>> event can trigger a new interrupt again.
>>
>> This is achieved here by looping over SSSR evaluation. We need to take
>> into account that SSCR1 may be changed by the transfer handler, thus
>> we
>> need to redo the mask calculation, at least regarding the volatile
>> interrupt enable bit (TIE).
> 
> Could you split this to two patches, one just move the code under
> question to a helper function (no functional change), the other does
> what you state in commit message here?

IMHO, factoring out some helper called from the loop in ssp_int won't be
a natural split due to the large number of local variables being shared
here. But maybe I'm not seeing the design you have in mind, so please
propose a useful helper function signature.

Thanks,
Jan

> 
>>
>> Signed-off-by: Jan Kiszka <jan.kiszka@...mens.com>
>> ---
>>  drivers/spi/spi-pxa2xx.c | 50 +++++++++++++++++++++++++++----------
>> -----------
>>  1 file changed, 28 insertions(+), 22 deletions(-)
>>
>> diff --git a/drivers/spi/spi-pxa2xx.c b/drivers/spi/spi-pxa2xx.c
>> index dd7b5b4..24bf549 100644
>> --- a/drivers/spi/spi-pxa2xx.c
>> +++ b/drivers/spi/spi-pxa2xx.c
>> @@ -737,6 +737,7 @@ static irqreturn_t ssp_int(int irq, void *dev_id)
>>  	struct driver_data *drv_data = dev_id;
>>  	u32 sccr1_reg;
>>  	u32 mask = drv_data->mask_sr;
>> +	irqreturn_t ret = IRQ_NONE;
>>  	u32 status;
>>  
>>  	/*
>> @@ -760,37 +761,42 @@ static irqreturn_t ssp_int(int irq, void
>> *dev_id)
>>  
>>  	sccr1_reg = pxa2xx_spi_read(drv_data, SSCR1);
>>  
>> -	/* Ignore possible writes if we don't need to write */
>> -	if (!(sccr1_reg & SSCR1_TIE))
>> -		mask &= ~SSSR_TFS;
>> -
>>  	/* Ignore RX timeout interrupt if it is disabled */
>>  	if (!(sccr1_reg & SSCR1_TINTE))
>>  		mask &= ~SSSR_TINT;
>>  
>> -	if (!(status & mask))
>> -		return IRQ_NONE;
>> +	while (1) {
>> +		/* Ignore possible writes if we don't need to write
>> */
>> +		if (!(sccr1_reg & SSCR1_TIE))
>> +			mask &= ~SSSR_TFS;
>>  
>> -	if (!drv_data->master->cur_msg) {
>> +		if (!(status & mask))
>> +			return ret;
>>  
>> -		pxa2xx_spi_write(drv_data, SSCR0,
>> -				 pxa2xx_spi_read(drv_data, SSCR0)
>> -				 & ~SSCR0_SSE);
>> -		pxa2xx_spi_write(drv_data, SSCR1,
>> -				 pxa2xx_spi_read(drv_data, SSCR1)
>> -				 & ~drv_data->int_cr1);
>> -		if (!pxa25x_ssp_comp(drv_data))
>> -			pxa2xx_spi_write(drv_data, SSTO, 0);
>> -		write_SSSR_CS(drv_data, drv_data->clear_sr);
>> +		if (!drv_data->master->cur_msg) {
>>  
>> -		dev_err(&drv_data->pdev->dev,
>> -			"bad message state in interrupt handler\n");
>> +			pxa2xx_spi_write(drv_data, SSCR0,
>> +					 pxa2xx_spi_read(drv_data,
>> SSCR0)
>> +					 & ~SSCR0_SSE);
>> +			pxa2xx_spi_write(drv_data, SSCR1,
>> +					 pxa2xx_spi_read(drv_data,
>> SSCR1)
>> +					 & ~drv_data->int_cr1);
>> +			if (!pxa25x_ssp_comp(drv_data))
>> +				pxa2xx_spi_write(drv_data, SSTO, 0);
>> +			write_SSSR_CS(drv_data, drv_data->clear_sr);
>>  
>> -		/* Never fail */
>> -		return IRQ_HANDLED;
>> -	}
>> +			dev_err(&drv_data->pdev->dev,
>> +				"bad message state in interrupt
>> handler\n");
>>  
>> -	return drv_data->transfer_handler(drv_data);
>> +			/* Never fail */
>> +			return IRQ_HANDLED;
>> +		}
>> +
>> +		ret |= drv_data->transfer_handler(drv_data);
>> +
>> +		status = pxa2xx_spi_read(drv_data, SSSR);
>> +		sccr1_reg = pxa2xx_spi_read(drv_data, SSCR1);
>> +	}
>>  }
>>  
>>  /*
> 

-- 
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