linux-kernel - Re: [PATCH v5 1/8] i2c: core: let adapters be notified of client attach/detach

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Message-ID: <Y6nRzXGm6ccvE6VM@pendragon.ideasonboard.com>
Date:   Mon, 26 Dec 2022 18:54:37 +0200
From:   Laurent Pinchart <laurent.pinchart@...asonboard.com>
To:     Andy Shevchenko <andriy.shevchenko@...el.com>
Cc:     Luca Ceresoli <luca.ceresoli@...tlin.com>,
        Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
        linux-media@...r.kernel.org, devicetree@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-i2c@...r.kernel.org,
        Rob Herring <robh+dt@...nel.org>,
        Krzysztof Kozlowski <krzysztof.kozlowski+dt@...aro.org>,
        Wolfram Sang <wsa@...nel.org>,
        Matti Vaittinen <Matti.Vaittinen@...rohmeurope.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Peter Rosin <peda@...ntia.se>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Michael Tretter <m.tretter@...gutronix.de>,
        Shawn Tu <shawnx.tu@...el.com>,
        Hans Verkuil <hverkuil@...all.nl>,
        Mike Pagano <mpagano@...too.org>,
        Krzysztof Hałasa <khalasa@...p.pl>,
        Marek Vasut <marex@...x.de>,
        Luca Ceresoli <luca@...aceresoli.net>
Subject: Re: [PATCH v5 1/8] i2c: core: let adapters be notified of client
 attach/detach

On Mon, Dec 19, 2022 at 11:48:51AM +0200, Andy Shevchenko wrote:
> On Mon, Dec 19, 2022 at 09:51:43AM +0100, Luca Ceresoli wrote:
> > On Sun, 11 Dec 2022 18:55:39 +0200 Laurent Pinchart wrote:
> > > On Thu, Dec 08, 2022 at 12:39:59PM +0200, Tomi Valkeinen wrote:
> 
> ...
> 
> > > This may be a stupid question, but couldn't you instead use the
> > > BUS_NOTIFY_ADD_DEVICE and BUS_NOTIFY_DEL_DEVICE bus notifiers ?
> > 
> > I'm not sure they would be the correct tool for this task. Bus
> > notifiers inform about new events on the 'struct bus_type, i.e. any
> > event on the global i2c bus type. In the i2c world this means being
> > notified about new _adapters_, which is exactly what
> > drivers/i2c/i2c-dev.c does.
> > 
> > Here, however, we need to be informed about new _clients_ being added
> > under a specific adapter.
> 
> This is for example exactly what ACPI integration in I2C framework does. But...
> 
> > I'm not sure whether the bus notifiers can
> > inform about new clients in addition of new adapters, but they at least
> > seem unable to provide per-adapter notification.
> 
> ...personally I don't like notifiers, they looks like overkill for this task.

But isn't this patch essentially implementing a custom notification
system ? If we need notifiers, why would it be better to add an ad-hoc
API for I2C instead of using bus notifiers ?

> > Does that seem correct?

-- 
Regards,

Laurent Pinchart