Re: [PATCH net-next v12 07/14] dpll: zl3073x: Add clock_id field

[Ivan Vecera <ivecera@redhat.com>]

On 02. 07. 25 2:01 odp., Jiri Pirko wrote:
> Wed, Jul 02, 2025 at 01:43:38PM +0200, ivecera@redhat.com wrote:
>>
>> On 02. 07. 25 12:31 odp., Jiri Pirko wrote:
>>> Sun, Jun 29, 2025 at 09:10:42PM +0200, ivecera@redhat.com wrote:
>>>> Add .clock_id to zl3073x_dev structure that will be used by later
>>>> commits introducing DPLL feature. The clock ID is required for DPLL
>>>> device registration.
>>>>
>>>> To generate this ID, use chip ID read during device initialization.
>>>> In case where multiple zl3073x based chips are present, the chip ID
>>>> is shifted and lower bits are filled by an unique value - using
>>>> the I2C device address for I2C connections and the chip-select value
>>>> for SPI connections.
>>>
>>> You say that multiple chips may have the same chip ID? How is that
>>> possible? Isn't it supposed to be unique?
>>> I understand clock ID to be invariant regardless where you plug your
>>> device. When you construct it from i2c address, sounds wrong.
>>
>> The chip id is not like serial number but it is like device id under
>> PCI. So if you will have multiple chips with this chip id you have to
>> distinguish somehow between them, this is the reason why I2C address
>> is added into the final value.
>>
>> Anyway this device does not have any attribute that corresponds to
>> clock id (as per our previous discussion) and it will be better to NOT
>> require clock id from DPLL core side.
> 
> Yes, better not to require it comparing to having it wrong.

It looks that using clock_id==0 is safe from DPLL API point of view.
The problem is if you will have multiple zl3073x based chips because
the driver would call dpll_device_get(0 /* clock_id */, channel, module)

For 1st chip (e.g. 2 channel) the driver will call:
dpll_device_get(0, 0, module);
dpll_device_get(0, 1, module);

and for the second the same that is wrong. The clock_id would help to
distinguish between them.

Wouldn't it be better to use a random number for clock_id from the
driver?

Ivan