Re: [PATCH v3 net-next 5/8] mfd: zl3073x: Add functions to work with register mailboxes

Lee Jones
2025-04-24T15:49:10Z

On Thu, 17 Apr 2025, Ivan Vecera wrote:

>
>
> On 17. 04. 25 3:27 odp., Andrew Lunn wrote:
> > > Anyway, I have a different idea... completely abstract mailboxes from the
> > > caller. The mailbox content can be large and the caller is barely interested
> > > in all registers from the mailbox but this could be resolved this way:
> > >
> > > The proposed API e.g for Ref mailbox:
> > >
> > > int zl3073x_mb_ref_read(struct zl3073x_dev *zldev, u8 index,
> > > struct zl3073x_mb_ref *mb);
> > > int zl3073x_mb_ref_write(struct zl3073x_dev *zldev, u8 index,
> > > struct zl3073x_mb_ref *mb);
> > >
> > > struct zl3073x_mb_ref {
> > > u32 flags;
> > > u16 freq_base;
> > > u16 freq_mult;
> > > u16 ratio_m;
> > > u16 ratio_n;
> > > u8 config;
> > > u64 phase_offset_compensation;
> > > u8 sync_ctrl;
> > > u32 esync_div;
> > > }
> > >
> > > #define ZL3073X_MB_REF_FREQ_BASE BIT(0)
> > > #define ZL3073X_MB_REF_FREQ_MULT BIT(1)
> > > #define ZL3073X_MB_REF_RATIO_M BIT(2)
> > > #define ZL3073X_MB_REF_RATIO_N BIT(3)
> > > #define ZL3073X_MB_REF_CONFIG BIT(4)
> > > #define ZL3073X_MB_REF_PHASE_OFFSET_COMPENSATION BIT(5)
> > > #define ZL3073X_MB_REF_SYNC_CTRL BIT(6)
> > > #define ZL3073X_MB_REF_ESYNC_DIV BIT(7)
> > >
> > > Then a reader can read this way (read freq and ratio of 3rd ref):
> > > {
> > > struct zl3073x_mb_ref mb;
> > > ...
> > > mb.flags = ZL3073X_MB_REF_FREQ_BASE |
> > > ZL3073X_MB_REF_FREQ_MULT |
> > > ZL3073X_MB_REF_RATIO_M |
> > > ZL3073X_MB_REF_RATIO_N;
> > > rc = zl3073x_mb_ref_read(zldev, 3, &mb);
> > > if (rc)
> > > return rc;
> > > /* at this point mb fields requested via flags are filled */
> > > }
> > > A writer similarly (write config of 5th ref):
> > > {
> > > struct zl3073x_mb_ref mb;
> > > ...
> > > mb.flags = ZL3073X_MB_REF_CONFIG;
> > > mb.config = FIELD_PREP(SOME_MASK, SOME_VALUE);
> > > rc = zl3073x_mb_ref_write(zldev, 5, &mb);
> > > ...
> > > /* config of 5th ref was commited */
> > > }
> > >
> > > The advantages:
> > > * no explicit locking required from the callers
> > > * locking is done inside mailbox API
> > > * each mailbox type can have different mutex so multiple calls for
> > > different mailbox types (e.g ref & output) can be done in parallel
> > >
> > > WDYT about this approach?
> >
> > I would say this is actually your next layer on top of the basic
> > mailbox API. This makes it more friendly to your sub driver and puts
> > all the locking in one place where it can easily be reviewed.
> >
> > One question would be, where does this code belong. Is it in the MFD,
> > or in the subdrivers? I guess it is in the subdrivers.
>
> No, it should be part of MFD because it does not make sense to implement API
> above in each sub-driver separately.
>
> Sub-driver would use this MB ABI for MB access and
> zl3073x_{read,write}_u{8,16,32,48} for non-MB registers.

Regardless of whether you decide to place the API in the sub-drivers or
not, it doesn't belong in MFD. 600 lines of any API is too heavyweight
to live here. If you can't justify placing it in Mailbox, my next
suggestion would be drivers/platform.

--
Lee Jones [李琼斯]