linux-kernel - Re: [PATCH v2 3/3] platform/chrome: cros_ec

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Date: Fri, 29 Mar 2024 17:13:08 +0200
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Pavan Holla <pholla@...omium.org>
Cc: Greg Kroah-Hartman <gregkh@...uxfoundation.org>, 
	Heikki Krogerus <heikki.krogerus@...ux.intel.com>, Benson Leung <bleung@...omium.org>, 
	Tzung-Bi Shih <tzungbi@...nel.org>, Guenter Roeck <groeck@...omium.org>, linux-kernel@...r.kernel.org, 
	linux-usb@...r.kernel.org, 
	Abhishek Pandit-Subedi <abhishekpandit@...omium.org>, chrome-platform@...ts.linux.dev
Subject: Re: [PATCH v2 3/3] platform/chrome: cros_ec_ucsi: Implement UCSI PDC driver

On Fri, 29 Mar 2024 at 17:09, Pavan Holla <pholla@...omium.org> wrote:
>
> Hi Dmitry,
>
> Thanks for the review.
>
> On Thu, Mar 28, 2024 at 8:32 AM Dmitry Baryshkov
> <dmitry.baryshkov@...aro.org> wrote:
> > While it's fine to use platform/chrome for platform drivers, please
> > place drivers which have a subsystem into the subsystem dir. I think we
> > don't want to hunt UCSI implementations all over the codebase. Please
> > use drivers/usb/typec/ucsi/ location for your driver. This also removes
> > a need for a global header.
>
> I agree with your assessment that drivers/usb/typec/ucsi/ is a good
> location for the driver currently. However, the driver is still in
> early stages of development. We may have to account for PDC/ EC quirks
> (we have multiple vendors), add FW update functionality outside the
> UCSI spec, or add PDC logging functionality. While I'd like to write
> separate drivers for those, some of this functionality will need to
> acquire a lock over communication to the PDC. Even if I were to write
> separate drivers for new functionality related to the PDC, maybe it's
> better for all ChromeOS PDC related drivers to reside in the same
> location. I am not sure what form this driver will take in the near
> future, thus I would prefer to keep it in platform/chrome. Maybe
> cros_ec_ucsi isn't the best name here, cros_ec_pdc probably conveys
> the intention better.

In such a case please consider using auxilliary device bus or MFD
cells to describe pdc / ucsi relationship. See how this is handled for
pmic-glink / ucsi_glink.
The drivers/platform should really be limited to simple drivers, which
don't have a better place. Otherwise it becomes a nightmare to handle
driver changes (this applies not only to the UCSI but also to other
drivers which have their own subsystem tree).

-- 
With best wishes
Dmitry