linux-kernel - Re: [PATCH v2] soundwire: bus: Don't filter slave alerts

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Date:   Tue, 18 Apr 2023 10:45:53 -0500
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Charles Keepax <ckeepax@...nsource.cirrus.com>, vkoul@...nel.org
Cc:     yung-chuan.liao@...ux.intel.com, sanyog.r.kale@...el.com,
        alsa-devel@...a-project.org, linux-kernel@...r.kernel.org,
        patches@...nsource.cirrus.com
Subject: Re: [PATCH v2] soundwire: bus: Don't filter slave alerts



On 4/18/23 09:06, Charles Keepax wrote:
> It makes sense to have only a single point responsible for ensuring
> that all currently pending IRQs are handled. The current code in
> sdw_handle_slave_alerts confusingly splits this process in two.  This
> code will loop until the asserted IRQs are cleared but it will only
> handle IRQs that were already asserted when it was called. This
> means the caller must also loop (either manually, or through its IRQ
> mechanism) until the IRQs are all handled. It makes sense to either do
> all the looping in sdw_handle_slave_alerts or do no looping there and
> let the host controller repeatedly call it until things are handled.
> 
> There are realistically two sensible host controllers, those that
> will generate an IRQ when the alert status changes and those
> that will generate an IRQ continuously whilst the alert status
> is high. The current code will work fine for the second of those
> systems but not the first with out additional looping in the host
> controller.  Removing the code that filters out new IRQs whilst
> the handler is running enables both types of host controller to be
> supported and simplifies the code. The code will still only loop up to
> SDW_READ_INTR_CLEAR_RETRY times, so it shouldn't be possible for it to
> get completely stuck handling IRQs forever, and if you are generating
> IRQs faster than you can handle them you likely have bigger problems
> anyway.
> 
> This fixes an issue on the Cadence SoundWire IP, which only generates
> IRQs on an alert status change, where an alert which arrives whilst
> another alert is being handled will never be handled and will block
> all future alerts from being handled.
> 
> Signed-off-by: Charles Keepax <ckeepax@...nsource.cirrus.com>

Makes sense to me, thanks for the patch.

Reviewed-by: Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>

> ---
> 
> Changes since v1:
>  - Update commit message
> 
> Thanks,
> Charles
> 
>  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 1ea6a64f8c4a5..338f4f0b5d0cc 100644
> --- a/drivers/soundwire/bus.c
> +++ b/drivers/soundwire/bus.c
> @@ -1588,7 +1588,7 @@ 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;
>  
> @@ -1745,9 +1745,9 @@ 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);
> @@ -1765,12 +1765,8 @@ 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;
>  
>  		/*