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

[Ivan Vecera]

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@xxxxxxxxxx> 
> > > > > > > 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