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

From: Richard Fitzgerald <rf@opensource.cirrus.com>
To: Pierre-Louis Bossart <pierre-louis.bossart@linux.intel.com>,
	<vkoul@kernel.org>, <yung-chuan.liao@linux.intel.com>,
	<lgirdwood@gmail.com>, <peter.ujfalusi@linux.intel.com>,
	<ranjani.sridharan@linux.intel.com>,
	<kai.vehmanen@linux.intel.com>, <daniel.baluta@nxp.com>,
	<sanyog.r.kale@intel.com>, <broonie@kernel.org>
Cc: <patches@opensource.cirrus.com>, <alsa-devel@alsa-project.org>,
	<linux-kernel@vger.kernel.org>,
	<sound-open-firmware@alsa-project.org>
Subject: Re: [PATCH 5/7] soundwire: intel: Don't disable interrupt until children are removed
Date: Tue, 13 Sep 2022 10:29:38 +0100	[thread overview]
Message-ID: <d0f32ac9-1de3-5047-b01a-04a68934a8a2@opensource.cirrus.com> (raw)
In-Reply-To: <9055c565-8616-8480-ea49-8db1b8707b34@linux.intel.com>

On 12/09/2022 18:12, Pierre-Louis Bossart wrote:
> 
> 
> On 9/12/22 17:36, Richard Fitzgerald wrote:
>> 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@opensource.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.
> 
> Ah yes, I forgot that part, thanks!
> 

... but I have noticed that there is a bug in
sdw_cdns_enable_interrupt(). It doesn't ensure that the
IRQ thread has seen the cdns->interrupt_enabled = false.
I'll add a patch to fix that when I re-push this chain.