linux-kernel - Re: [PATCH 5/7] soundwire: intel: Don't disable interrupt until children are removed

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Date:   Mon, 12 Sep 2022 16:36:09 +0100
From:   Richard Fitzgerald <rf@...nsource.cirrus.com>
To:     Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>,
        <vkoul@...nel.org>, <yung-chuan.liao@...ux.intel.com>,
        <lgirdwood@...il.com>, <peter.ujfalusi@...ux.intel.com>,
        <ranjani.sridharan@...ux.intel.com>,
        <kai.vehmanen@...ux.intel.com>, <daniel.baluta@....com>,
        <sanyog.r.kale@...el.com>, <broonie@...nel.org>
CC:     <patches@...nsource.cirrus.com>, <alsa-devel@...a-project.org>,
        <linux-kernel@...r.kernel.org>,
        <sound-open-firmware@...a-project.org>
Subject: Re: [PATCH 5/7] soundwire: intel: Don't disable interrupt until
 children are removed

On 12/09/2022 11:53, Pierre-Louis Bossart wrote:
> 
> 
> On 9/7/22 12:14, Richard Fitzgerald wrote:
>> The cadence_master code needs the interrupt to complete message transfers.
>> When the bus driver is being removed child drivers are removed, and their
>> remove actions might need bus transactions.
>>
>> Use the sdw_master_ops.remove callback to disable the interrupt handling
>> only after the child drivers have been removed.
>>
>> Signed-off-by: Richard Fitzgerald <rf@...nsource.cirrus.com>
>> ---
>>   drivers/soundwire/intel.c | 9 ++++++++-
>>   1 file changed, 8 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/soundwire/intel.c b/drivers/soundwire/intel.c
>> index 01be62fa6c83..d5e723a9c80b 100644
>> --- a/drivers/soundwire/intel.c
>> +++ b/drivers/soundwire/intel.c
>> @@ -1255,6 +1255,13 @@ static int intel_prop_read(struct sdw_bus *bus)
>>   	return 0;
>>   }
>>   
>> +static void intel_bus_remove(struct sdw_bus *bus)
>> +{
>> +	struct sdw_cdns *cdns = bus_to_cdns(bus);
>> +
>> +	sdw_cdns_enable_interrupt(cdns, false);
> 
> don't you need to check for any on-going transactions on the bus?
>

As all the child drivers have removed, I think the only other place that
can generate bus transactions is the PING handler but
sdw_cdns_enable_interrupt(false) calls cancel_work_sync() to
cancel the cdns->work and it sets a flag so that it will not be
re-queued.

> I wonder if there could be a corner case where there are no child
> devices but still a device physically attached to the bus. I am not sure
> if the 'no devices left' is a good-enough indication of no activity on
> the bus.
>

As above - yes there could, but sdw_cdns_enable_interrupt(false) will
cancel the work and stop it being re-queued.

>> +}
>> +
>>   static struct sdw_master_ops sdw_intel_ops = {
>>   	.read_prop = sdw_master_read_prop,
>>   	.override_adr = sdw_dmi_override_adr,
>> @@ -1264,6 +1271,7 @@ static struct sdw_master_ops sdw_intel_ops = {
>>   	.set_bus_conf = cdns_bus_conf,
>>   	.pre_bank_switch = intel_pre_bank_switch,
>>   	.post_bank_switch = intel_post_bank_switch,
>> +	.remove = intel_bus_remove,
>>   };
>>   
>>   static int intel_init(struct sdw_intel *sdw)
>> @@ -1502,7 +1510,6 @@ static void intel_link_remove(struct auxiliary_device *auxdev)
>>   	 */
>>   	if (!bus->prop.hw_disabled) {
>>   		intel_debugfs_exit(sdw);
>> -		sdw_cdns_enable_interrupt(cdns, false);
>>   		snd_soc_unregister_component(dev);
>>   	}
>>   	sdw_bus_master_delete(bus);