Re: [PATCH v1 1/1] i2c: cht-wc: Use fwnode for the controller and IRQ domain

[Hans de Goede <hdegoede@redhat.com>]

Hi,

On 2/24/21 1:51 PM, Andy Shevchenko wrote:
> On Tue, Feb 23, 2021 at 08:25:35PM +0100, Hans de Goede wrote:
>> On 2/23/21 6:22 PM, Andy Shevchenko wrote:
>>> It's better to describe the I²C controller and associated IRQ domain with
>>> fwnode, so they will find their place in the hierarchy in sysfs and also
>>> make easier to debug.
>>>
>>> Signed-off-by: Andy Shevchenko <andriy.shevchenko@linux.intel.com>
>>> ---
>>>
>>> Hans, unfortunately I have no device at hand with INT34D3. This is only compile
>>> tested in that sense. Also I would like to hear if you like the idea in general.
>>>
>>>  drivers/i2c/busses/i2c-cht-wc.c | 6 ++++--
>>>  1 file changed, 4 insertions(+), 2 deletions(-)
>>>
>>> diff --git a/drivers/i2c/busses/i2c-cht-wc.c b/drivers/i2c/busses/i2c-cht-wc.c
>>> index f80d79e973cd..dbf55842b0dc 100644
>>> --- a/drivers/i2c/busses/i2c-cht-wc.c
>>> +++ b/drivers/i2c/busses/i2c-cht-wc.c
>>> @@ -303,6 +303,7 @@ static struct bq24190_platform_data bq24190_pdata = {
>>>  static int cht_wc_i2c_adap_i2c_probe(struct platform_device *pdev)
>>>  {
>>>  	struct intel_soc_pmic *pmic = dev_get_drvdata(pdev->dev.parent);
>>> +	struct fwnode_handle *fwnode = dev_fwnode(&pdev->dev);
>>
>> So this will point to the ACPi-companion fwnode of the CHT Whiskey Cove PMIC
>> controller.
> 
> Right.
> 
>>>  	struct cht_wc_i2c_adap *adap;
>>>  	struct i2c_board_info board_info = {
>>>  		.type = "bq24190",
>>> @@ -333,6 +334,7 @@ static int cht_wc_i2c_adap_i2c_probe(struct platform_device *pdev)
>>>  	strlcpy(adap->adapter.name, "PMIC I2C Adapter",
>>>  		sizeof(adap->adapter.name));
>>>  	adap->adapter.dev.parent = &pdev->dev;
>>> +	set_primary_fwnode(&adap->adapter.dev, fwnode);
>>
>> So now we have the main PMIC device i2c-client, the platform-device instantiated
>> for the MFD-cell for the PMIC's builtin I2C-controller; and the device instantiated
>> for the adapter-device all 3 share the same ACPI-companion fwnode.
> 
> Okay, this step in this patch maybe not needed (or should be a separate change,
> but I don't see clearly what would be the benefit out of it).
> 
>>>  	/* Clear and activate i2c-adapter interrupts, disable client IRQ */
>>>  	adap->old_irq_mask = adap->irq_mask = ~CHT_WC_EXTCHGRIRQ_ADAP_IRQMASK;
>>> @@ -350,8 +352,8 @@ static int cht_wc_i2c_adap_i2c_probe(struct platform_device *pdev)
>>>  		return ret;
>>>  
>>>  	/* Alloc and register client IRQ */
>>> -	adap->irq_domain = irq_domain_add_linear(pdev->dev.of_node, 1,
>>> -						 &irq_domain_simple_ops, NULL);
>>> +	adap->irq_domain = irq_domain_create_linear(fwnode, 1,
>>> +						    &irq_domain_simple_ops, NULL);
>>
>> Hmm, not sure this is right, admittedly the old code looks weird too, but now we
>> are creating a second irq_domain at the same level as the irq_domain created for
>> the IRQ-chip part of the PMIC. But this is really more of a child-domain of just
>> the I2C-controller MFD-cell. The IRQ-CHIP part of the PMIC has a single IRQ for the
>> I2C controller which gets raised both on i2c-transfer completions and when the
>> pin on the PMIC which is reserved as input for the IRQ coming out of the charger-chip
>> gets triggered.
>>
>> IOW we have this:
>>
>>
>>                PMIC
>>                  |
>>     ------------------------------
>>     |       |        |           |
>>    IRQ1   IRQ2      IRQ3       I2C-IRQ
>>                                  |
>>                    ----------------------------------
>>                    |        |         |             |
>>                  READIRQ   WRIRQ    NACKIRQ     CLIENT-IRQ
>>
>> Where READIRQ, WRIRQ and NACKIRQ are directly consumed
>> and the CLIENT-IRQ is being represented as a single IRQ on
>> a new irqchip so that we can pass it along to the i2c-driver
>> for the charger-chip which is connected to the Whiskey Cove's
>> builtin I2C controller.
>>
>> But doing as you suggest would model the IRQs as:
>>
>>                PMIC
>>                  |
>>     --------------------------------------------------
>>     |       |        |           |                    |
>>    IRQ1   IRQ2      IRQ3       I2C-IRQ           CLIENT-IRQ
>>
>> Which is not the same really. I guess it is better then what we
>> have though ?
> 
> Hmm... There should not be difference in the hierarchy. add_linear ==
> create_linear. The propagation of *device* (not an IRQ) fwnode is just
> convenient way to have IRQ domain be named (instead of 'unknown-N' or so).
> Maybe I have read __irq_domain_add() code wrongly.

Sorry, this is probably my bad. The first ASCII-art which I posted is
how things actually work in HW. The second one is how I assumed that
things would look like in some nested representation of the IRQ-domains
given that all the IRQs mentioned in the ASCII-art now use the same fwnode
as parent for their domain. But poking around in sysfs I don't see any
hierarchical representation of the domains at all. Actually I cannot
find any representation of the IRQ domains inside sysfs (I've never
looked at / into this before) ?

If what you say is right and the fwnode is only used to set a name (where can
I see those names ?) then your patch is probably correct.

> Nevertheless, thinking more about it, why we don't add an IRQ chip via regmap
> IRQ API?

There already is a regmap IRQ chip associated with the MFD device and the
IRQ handling required here is somewhat tricky (see the comments in the driver)
so I would prefer to keep this as is.

>> Note I can test any changes made here, but I'm not 100% convinced that
>> the current version of this patch is correct.
> 
> If we settle on the idea first. I'm (slowly) looking forward to check another
> CherryTrail device we have at the lab, but we lack of some (power) equipment
> right now to setup it properly. I hope it may have the Whiskey Cove PMIC there.

More testing is always welcome :)   With that said, testing these changes really
is not a lot of work for me.

Regards,

Hans