Re: [PATCH net-next v7 8/8] mfd: zl3073x: Register DPLL sub-device during init

[Ivan Vecera <ivecera@redhat.com>]

On 13. 05. 25 12:47 odp., Ivan Vecera wrote:
> On 13. 05. 25 11:41 dop., Lee Jones wrote:
>> On Mon, 12 May 2025, Ivan Vecera wrote:
>>
>>> On 07. 05. 25 5:26 odp., Lee Jones wrote:
>>>> On Wed, 07 May 2025, Andy Shevchenko wrote:
>>>>
>>>>> On Wed, May 07, 2025 at 03:56:37PM +0200, Ivan Vecera wrote:
>>>>>> On 07. 05. 25 3:41 odp., Andy Shevchenko wrote:
>>>>>>> On Wed, May 7, 2025 at 3:45 PM Ivan Vecera <ivecera@redhat.com> 
>>>>>>> wrote:
>>>>>
>>>>> ...
>>>>>
>>>>>>>> +static const struct zl3073x_pdata 
>>>>>>>> zl3073x_pdata[ZL3073X_MAX_CHANNELS] = {
>>>>>>>> +       { .channel = 0, },
>>>>>>>> +       { .channel = 1, },
>>>>>>>> +       { .channel = 2, },
>>>>>>>> +       { .channel = 3, },
>>>>>>>> +       { .channel = 4, },
>>>>>>>> +};
>>>>>>>
>>>>>>>> +static const struct mfd_cell zl3073x_devs[] = {
>>>>>>>> +       ZL3073X_CELL("zl3073x-dpll", 0),
>>>>>>>> +       ZL3073X_CELL("zl3073x-dpll", 1),
>>>>>>>> +       ZL3073X_CELL("zl3073x-dpll", 2),
>>>>>>>> +       ZL3073X_CELL("zl3073x-dpll", 3),
>>>>>>>> +       ZL3073X_CELL("zl3073x-dpll", 4),
>>>>>>>> +};
>>>>>>>
>>>>>>>> +#define ZL3073X_MAX_CHANNELS   5
>>>>>>>
>>>>>>> Btw, wouldn't be better to keep the above lists synchronised like
>>>>>>>
>>>>>>> 1. Make ZL3073X_CELL() to use indexed variant
>>>>>>>
>>>>>>> [idx] = ...
>>>>>>>
>>>>>>> 2. Define the channel numbers
>>>>>>>
>>>>>>> and use them in both data structures.
>>>>>>>
>>>>>>> ...
>>>>>>
>>>>>> WDYM?
>>>>>>
>>>>>>> OTOH, I'm not sure why we even need this. If this is going to be
>>>>>>> sequential, can't we make a core to decide which cell will be given
>>>>>>> which id?
>>>>>>
>>>>>> Just a note that after introduction of PHC sub-driver the array 
>>>>>> will look
>>>>>> like:
>>>>>> static const struct mfd_cell zl3073x_devs[] = {
>>>>>>          ZL3073X_CELL("zl3073x-dpll", 0),  // DPLL sub-dev for chan 0
>>>>>>          ZL3073X_CELL("zl3073x-phc", 0),   // PHC sub-dev for chan 0
>>>>>>          ZL3073X_CELL("zl3073x-dpll", 1),  // ...
>>>>>>          ZL3073X_CELL("zl3073x-phc", 1),
>>>>>>          ZL3073X_CELL("zl3073x-dpll", 2),
>>>>>>          ZL3073X_CELL("zl3073x-phc", 2),
>>>>>>          ZL3073X_CELL("zl3073x-dpll", 3),
>>>>>>          ZL3073X_CELL("zl3073x-phc", 3),
>>>>>>          ZL3073X_CELL("zl3073x-dpll", 4),
>>>>>>          ZL3073X_CELL("zl3073x-phc", 4),   // PHC sub-dev for chan 4
>>>>>> };
>>>>>
>>>>> Ah, this is very important piece. Then I mean only this kind of change
>>>>>
>>>>> enum {
>>>>>     // this or whatever meaningful names
>>>>>     ..._CH_0    0
>>>>>     ..._CH_1    1
>>>>>     ...
>>>>> };
>>>>>
>>>>> static const struct zl3073x_pdata 
>>>>> zl3073x_pdata[ZL3073X_MAX_CHANNELS] = {
>>>>>          { .channel = ..._CH_0, },
>>>>>          ...
>>>>> };
>>>>>
>>>>> static const struct mfd_cell zl3073x_devs[] = {
>>>>>          ZL3073X_CELL("zl3073x-dpll", ..._CH_0),
>>>>>          ZL3073X_CELL("zl3073x-phc", ..._CH_0),
>>>>>          ...
>>>>> };
>>>>
>>>> This is getting hectic.  All for a sequential enumeration.  Seeing as
>>>> there are no other differentiations, why not use IDA in the child
>>>> instead?
>>>
>>> For that, there have to be two IDAs, one for DPLLs and one for PHCs...
>>
>> Sorry, can you explain a bit more.  Why is this a problem?
>>
>> The IDA API is very simple.
>>
>> Much better than building your own bespoke MACROs.
> 
> I will try to explain this in more detail... This MFD driver handles
> chip family ZL3073x where the x == number of DPLL channels and can
> be from <1, 5>.
> 
> The driver creates 'x' DPLL sub-devices during probe and has to pass
> channel number that should this sub-device use. Here can be used IDA
> in DPLL sub-driver:
> e.g. ida_alloc_max(zldev->channels, zldev->max_channels, GFP_KERNEL);
> 
> This way the DPLL sub-device get its own unique channel ID to use.
> 
> The situation is getting more complicated with PHC sub-devices because
> the chip can provide UP TO 'x' PHC sub-devices depending on HW
> configuration. To handle this the MFD driver has to check this HW config
> for particular channel if it is capable to provide PHC functionality.
> 
> E.g. ZL30735 chip has 5 channels, in this case the MFD driver should
> create 5 DPLL sub-devices. And then lets say channel 0, 2 and 4 are
> PHC capable. Then the MFD driver should create 3 PHC sub-devices and
> pass 0, 2 resp. 4 for them.
> 
> In that case IDA cannot be simply used as the allocation is not
> sequential.
> 
> So yes, for DPLL sub-devices IDA could be used but for the PHCs another
> approach (platform data) has to be used.
> 
> There could be a hacky way to use IDA for PHCs: MFD would create PHC
> sub-devices for all channels and PHC sub-driver would check the channel
> config during probe and if the channel is not capable then returns
> -ENODEV. But I don't think this is good idea to create MFD cells this
> way.
> 
> Thanks for advices.
> 
> Ivan

Lee, any comment? What about my proposal in v8?

Thanks,
Ivan