linux-kernel - Re: [PATCH v2 2/3] spi: pxa2xx: Prepare for edge-triggered interrupts

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Date:   Mon, 16 Jan 2017 20:46:05 +0100
From:   Jan Kiszka <jan.kiszka@...mens.com>
To:     Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Mark Brown <broonie@...nel.org>
Cc:     linux-spi@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        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@...ux.intel.com>
Subject: Re: [PATCH v2 2/3] spi: pxa2xx: Prepare for edge-triggered interrupts

On 2017-01-16 20:07, Andy Shevchenko wrote:
> On Mon, 2017-01-16 at 19:44 +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).
>>
> 
> So, more comments/questions below.
> 
>>  
>>  	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) {
> 
> Can we switch to do-while and move previous block here?

Don't see how this would help (without duplicating more code).

> Btw, can TINTE
> bit be set again during a loop?

Nope, it's statically set, at least so far.

What we could do is simply restarting ssp_int

> 
>> +		/* Ignore possible writes if we don't need to write
>> */
>> +		if (!(sccr1_reg & SSCR1_TIE))
>> +			mask &= ~SSSR_TFS;
>>  
>> -	if (!drv_data->master->cur_msg) {
>> -		handle_bad_msg(drv_data);
>> -		/* Never fail */
>> -		return IRQ_HANDLED;
>> -	}
>> +		if (!(status & mask))
>> +			return ret;
>> +
>> +		if (!drv_data->master->cur_msg) {
>> +			handle_bad_msg(drv_data);
>> +			/* Never fail */
>> +			return IRQ_HANDLED;
>> +		}
>> +
> 
>> +		ret |= drv_data->transfer_handler(drv_data);
> 
> So, we might call handler several times. This needs to be commented in
> the code why you do so.

I can move the commit log into the code.

> 
>>  
>> -	return drv_data->transfer_handler(drv_data);
>> +		status = pxa2xx_spi_read(drv_data, SSSR);
> 
> Would it be possible to get all 1:s from the register
> (something/autosuspend just powered off it by timeout?) ?
> 

Not sure if that can happen, but I guess it would be simpler and more
readable to simply do this instead:

	while (1) {
		/*
		 * If the device is not yet in RPM suspended state and we get an
		 * interrupt that is meant for another device, check if status
		 * bits are all set to one. That means that the device is
		 * already powered off.
		 */
		status = pxa2xx_spi_read(drv_data, SSSR);
		if (status == ~0)
			return ret;

		sccr1_reg = pxa2xx_spi_read(drv_data, SSCR1);

		/* Ignore RX timeout interrupt if it is disabled */
		if (!(sccr1_reg & SSCR1_TINTE))
			mask &= ~SSSR_TINT;

		/* Ignore possible writes if we don't need to write */
		if (!(sccr1_reg & SSCR1_TIE))
			mask &= ~SSSR_TFS;

		if (!(status & mask))
			return ret;

		if (!drv_data->master->cur_msg) {
			handle_bad_msg(drv_data);
			/* Never fail */
			return IRQ_HANDLED;
		}

		ret |= drv_data->transfer_handler(drv_data);
	}


i.e. preserve the current structure, just add the loop.

Jan

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