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SubjectRe: [PATCH v3 02/13] mfd: wcd9335: add support to wcd9335 core

On 12/09/18 11:59, Lee Jones wrote:
>> On 12/09/18 09:58, Lee Jones wrote:
>>>>>> +static const struct mfd_cell wcd9335_devices[] = {
>>>>>> + { .name = "wcd9335-codec", },
>>>>>> +};
>>>>> Are there more devices to come?
>>>> Yes, that is the plan, we are kind of limited in hardware setup to test few
>>>> things like soundwire controller. We are exploring other ways to test these.
>>> I normally don't accept MFDs with just one device enabled. Since it's
>>> not really an MFD (M == Multi) until it has more than one function.
>> WCD9335 Codec hw itself has multiple hw blocks.
>> If the issue is about adding more entries to mfd cells then we should be
>> able to add below entry:
>> { .name = "wcd9335-soundwire-controller", },
>> Actual driver for soundwire controller is not something We can test with
>> regular dragon boards, it needs special hw for smart speakers. Once we have
>> that we can test and post the drivers for that.
>> Otherwise
>> Are you suggesting that I move everything to sound/soc/codecs and then back
>> to mfd once soundwire controller driver is added?
> My preference would be for you to add at least one other (tested)
> device. However, in your case I know where you live, so I can throw
> tomatoes at your house if you don't upstream more device support
> promptly!;)
> When will you be enabling more devices? If the answer is 'never',
> then creating an MFD is a waste of time.

Vinod Koul is exploring this and ATM we are trying to sort out the hw
setup. Hopefully we should be sorted with Qcom help!

>>> [...]
>>>>>> + struct device_node *ifc_dev_np;
>>>>> ifc isn't very forthcoming. Any way you can improve the name?
>>>> ifc was suggested in dt bindings by Rob, I can proably rename to
>>>> interface_node.
>>> ifc is a horrible variable name - just sayin'.
>>> [...]
>>>>>> + ret = wcd9335_bring_up(wcd);
>>>>> So the device_status call-back brings up the hardware?
>>>> device status reports the device status at runtime. We can not communicate
>>>> with the device until it is up, enumerated by slimbus and a logical address
>>>> is assigned to it. So the best place to initialize it is in status callback
>>>> where all the above are expected to be done.
>>> Right, I understand what's happening. I just think the semantics are
>>> wrong. The Subsystem (I'm assuming it's a Subsystem) requests for
>>> status and it ends up initiating a start-up sequence. Just from a
>>> purist's point of view (I understand that it "works"), it's not good
>>> practice.
>>>> Probe is expected to setup the external configurations like regulators/pins
>>>> and so on which gets the device out of reset and ready to be enumerated by
>>>> the slimbus controller.
>>> I suggest fully starting the device in probe() is a better approach.
>> Its catch-22 situation, without device being powered up and reset correctly
>> there is no way to enumerate it.
> Isn't power-up and reset also done in probe()?
> What am I missing?

There are two parts for device to be ready to talk at bus level:
1> power up and reset,
2> enumerate and assign a logical address by the slimbus controller.

First part as you said is already done in probe.
When second part happens when status callback is invoked, that is when
the slimdevice is ready for any kind of communication at bus level.


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