Re: [PATCH v7 0/7] i2c-atr and FPDLink

[Luca Ceresoli]

Hi Andy,

On Wed, 18 Jan 2023 19:43:23 +0200
Andy Shevchenko <andriy.shevchenko@xxxxxxxxx> wrote:

> On Wed, Jan 18, 2023 at 07:28:20PM +0200, Tomi Valkeinen wrote:
> > On 18/01/2023 18:01, Andy Shevchenko wrote:  
> > > On Wed, Jan 18, 2023 at 02:40:24PM +0200, Tomi Valkeinen wrote:  
> > > > Hi,
> > > > 
> > > > You can find the v6 from:
> > > > 
> > > > https://lore.kernel.org/all/20230105140307.272052-1-tomi.valkeinen@xxxxxxxxxxxxxxxx/
> > > > 
> > > > Main changes:
> > > > 
> > > > * i2c-atr: Use bus notifier. This allows us to drop the patch that adds
> > > >    the attach_client/detach_client callbacks. On the downside, it removes
> > > >    the option for error handling if the translation setup fails, and also
> > > >    doesn't provide us the pointer to the i2c_board_info. I belive both
> > > >    are acceptable downsides.
> > > > 
> > > > * Use fwnode in the fpdlink drivers instead of OF
> > > > 
> > > > * Addressed all the review comments (I hope)
> > > > 
> > > > * Lots of cosmetic or minor fixes which I came up while doing the fwnode
> > > >    change  
> > > 
> > > I believe my comments to the first driver applies to the next two, so please
> > > address them whenever you are agree / it's possible / it makes sense.
> > > 
> > > About ATR implementation. We have the i2c bus (Linux representation of
> > > the driver model) and i2c_adapter and i2c_client objects there. Can't we
> > > have an i2c_client_aliased in similar way and be transparent with users?  
> 
> > Can you clarify what you mean here?
> > 
> > The i2c_clients are not aware of the i2c-atr. They are normal i2c clients.
> > The FPD-Link drivers are aware of the ATR, as the FPD-Link hardware contains
> > the ATR support.  
> 
> Can't that hardware be represented as I2C adapter? In such case the ATR specifics
> can be hidden from the client (drivers).
> 
> I'm worrying about code duplication and other things that leak into drivers as
> ATR callbacks.

Which callbacks do you refer to? i2c_atr_ops? I don't think we can do
without the attach/detach_client ones, it's where the driver-specific
implementation is hooked for the generic ATR infra to call it.

However now I noticed the select/deselect ops are still there. IIRC
they are not used by any driver and in the past the plan was to just
remove them. Tomi, do you think there is a good reason to keep them?

> It might be that I didn't get how hw exactly functioning on this
> level and why we need those callbacks.

As far as "how hw exactly works", in case you haven't seen that, the
best explanation I was able to give is in my ELCE 2019 talk, at minute
~22. It's a 2-3 minute watch. The slides have pointers to other talks
and discussion.

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com