linux-kernel - Re: [PATCH 2/2] soundwire: bus: Allow SoundWire peripherals to register IRQ handlers

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Message-ID: <881088ad-95d7-2462-20d2-72a6a9d3ba68@linux.intel.com>
Date:   Fri, 20 Jan 2023 10:20:50 -0600
From:   Pierre-Louis Bossart <pierre-louis.bossart@...ux.intel.com>
To:     Charles Keepax <ckeepax@...nsource.cirrus.com>
Cc:     vkoul@...nel.org, 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 2/2] soundwire: bus: Allow SoundWire peripherals to
 register IRQ handlers



On 1/20/23 03:59, Charles Keepax wrote:
> On Thu, Jan 19, 2023 at 11:12:04AM -0600, Pierre-Louis Bossart wrote:
>> No objection on this addition, just a couple of comments to improve it:
>>
>>>  EXPORT_SYMBOL(sdw_bus_master_add);
>>> @@ -158,6 +183,8 @@ static int sdw_delete_slave(struct device *dev, void *data)
>>>  	mutex_lock(&bus->bus_lock);
>>>  
>>>  	if (slave->dev_num) { /* clear dev_num if assigned */
>>> +		irq_dispose_mapping(irq_find_mapping(bus->domain, slave->dev_num));
>>> +
>>
>> could this be done conditionally. e.g.
>>
>> if (slave->prop.irq)
>>     irq_dispose_mapping(irq_find_mapping(bus->domain, slave->dev_num));
>>
>>> +			slave->irq = irq_create_mapping(bus->domain, dev_num);
>>> +			if (!slave->irq) {
>>> +				dev_err(bus->dev, "Failed to map IRQ\n");
>>> +				return -EINVAL;
>>> +			}
>>
>> ...and here....
>>
>> if (slave->prop.irq) {
>> 	slave->irq = irq_create_mapping(bus->domain, dev_num);
>> 	if (!slave->irq) {
>> 		dev_err(bus->dev, "Failed to map IRQ\n");
>> 		return -EINVAL;
>> 	}
>> }
>>
> 
> Yeah I am happy to make those conditional, I guess it is cleaner
> to not map IRQs if they wont be used.

ok

> 
>>> @@ -369,6 +371,7 @@ struct sdw_dpn_prop {
>>>   * @clock_reg_supported: the Peripheral implements the clock base and scale
>>>   * registers introduced with the SoundWire 1.2 specification. SDCA devices
>>>   * do not need to set this boolean property as the registers are required.
>>> + * @irq: call actual IRQ handler on slave, as well as callback
>>>   */
>>>  struct sdw_slave_prop {
>>>  	u32 mipi_revision;
>>> @@ -393,6 +396,7 @@ struct sdw_slave_prop {
>>>  	u8 scp_int1_mask;
>>>  	u32 quirks;
>>>  	bool clock_reg_supported;
>>> +	bool irq;
>>
>> this can be confused with the 'wake_capable' property.
>>
>> maybe 'out_of_band_irq' ?
>>
> 
> Yes I struggle on the name a bit and then just gave up and
> went with plain "irq", hard to know what to call it. Not sure
> out_of_band is quite right since it not really out of band,
> handle_nested_irq pretty much basically boils down to a function
> call really. Maybe something like "map_irq", or "use_domain_irq"?

Naming is hard. I use 'in-band wake' for SoundWire-based notifications,
so I used 'out-of-band' for non-SoundWire stuff.

use_domain_irq sounds goods to me, it's different enough that confusions
are not possible.

>> There should be an explanation and something checking that both are not
>> used concurrently.
> 
> I will try to expand the explanation a litte, but I dont see any
> reason to block calling both handlers, no ill effects would come
> for a driver having both and it is useful if any soundwire
> specific steps are needed that arn't on other control buses.

I think it's problematic if the peripheral tries to wake-up the manager
from clock-stop with both an in-band wake (i.e. drive the data line
high) and a separate GPIO-based interrupt. It's asking for trouble IMHO.
We spent hours in the MIPI team to make sure there were no races between
the manager-initiated restarts and peripheral-initiated restarts, adding
a 3rd mechanism in the mix gives me a migraine already.