Re: [PATCH 1/2] soundwire: bus: Don't filter slave alerts

[Pierre-Louis Bossart]

On 1/19/23 10:51, Charles Keepax wrote:
> Currently the SoundWire core will loop handling slave alerts but it will
> only handle those present when the alert was first raised. This causes
> some issues with the Cadence SoundWire IP, which only generates an IRQ
> when alert changes state. This means that if a new alert arrives whilst
> old alerts are being handled it will not be handled in the currently
> loop and then no further alerts will be processed since alert never
> changes state to trigger a new IRQ.
> 
> Correct this issue by allowing the core to handle all pending alerts in
> the IRQ handling loop. The code will still only loop up to
> SDW_READ_INTR_CLEAR_RETRY times, so it shouldn't be possible for it get
> completely stuck and if you are generating IRQs faster than you can
> handle them you likely have bigger problems anyway.

The change makes sense, but it's a bit odd to change the way the
interrupts are handled because of a specific design. The bus should be
able to deal with various designs, not force a one-size-fits-all policy
that may not be quite right in all cases.

Could we have a new flag at the bus level that says that peripheral
interrupts are not filtered, and set if for the Intel case?

We could similarly make the SDW_READ_INTR_CLEAR_RETRY constant
bus/platform specific. The SoundWire spec mandates that we re-read the
status after clearing the interrupt, but it doesn't say how to deal with
recurring interrupts.

> Signed-off-by: Charles Keepax <ckeepax@xxxxxxxxxxxxxxxxxxxxx>
> ---
>  drivers/soundwire/bus.c | 12 ++++--------
>  1 file changed, 4 insertions(+), 8 deletions(-)
> 
> diff --git a/drivers/soundwire/bus.c b/drivers/soundwire/bus.c
> index 633d411b64f35..daee2cca94a4d 100644
> --- a/drivers/soundwire/bus.c
> +++ b/drivers/soundwire/bus.c
> @@ -1560,7 +1560,7 @@ static int sdw_handle_slave_alerts(struct sdw_slave *slave)
>  	unsigned long port;
>  	bool slave_notify;
>  	u8 sdca_cascade = 0;
> -	u8 buf, buf2[2], _buf, _buf2[2];
> +	u8 buf, buf2[2];
>  	bool parity_check;
>  	bool parity_quirk;
>  
> @@ -1716,9 +1716,9 @@ static int sdw_handle_slave_alerts(struct sdw_slave *slave)
>  				"SDW_SCP_INT1 recheck read failed:%d\n", ret);
>  			goto io_err;
>  		}
> -		_buf = ret;
> +		buf = ret;
>  
> -		ret = sdw_nread_no_pm(slave, SDW_SCP_INTSTAT2, 2, _buf2);
> +		ret = sdw_nread_no_pm(slave, SDW_SCP_INTSTAT2, 2, buf2);
>  		if (ret < 0) {
>  			dev_err(&slave->dev,
>  				"SDW_SCP_INT2/3 recheck read failed:%d\n", ret);
> @@ -1736,12 +1736,8 @@ static int sdw_handle_slave_alerts(struct sdw_slave *slave)
>  		}
>  
>  		/*
> -		 * Make sure no interrupts are pending, but filter to limit loop
> -		 * to interrupts identified in the first status read
> +		 * Make sure no interrupts are pending
>  		 */
> -		buf &= _buf;
> -		buf2[0] &= _buf2[0];
> -		buf2[1] &= _buf2[1];
>  		stat = buf || buf2[0] || buf2[1] || sdca_cascade;
>  
>  		/*