linux-kernel - Re: [PATCH v1 06/15] i2c: acpi: Assign fwnode for devices created via i2c_acpi_new

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Date:   Wed, 21 Nov 2018 15:35:49 +0200
From:   Andy Shevchenko <andriy.shevchenko@...ux.intel.com>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     Darren Hart <dvhart@...radead.org>,
        platform-driver-x86@...r.kernel.org,
        "Rafael J. Wysocki" <rjw@...ysocki.net>,
        linux-acpi@...r.kernel.org, Jonathan Cameron <jic23@...nel.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        linux-i2c@...r.kernel.org,
        Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v1 06/15] i2c: acpi: Assign fwnode for devices created
 via i2c_acpi_new_device()

On Wed, Nov 21, 2018 at 12:44:27PM +0100, Hans de Goede wrote:
> On 20-11-18 16:59, Andy Shevchenko wrote:
> > i2c_acpi_new_device() doesn't assign fwnode like it's done, for example,
> > in i2c_acpi_register_devices() path.
> > 
> > Assign fwnode in i2c_acpi_new_device() as it's done elsewhere.

> As already mentioned in my reply to the cover letter, a NACK from me for
> this one.
> 
> The problem is that this causes the fwnode to be shared by all the
> "struct device"-s (embedded in the i2c-clients created).
> 
> This in itself is not necessarily a problem, but it does become a
> problem when combined with using device_add_properties as
> intel_cht_int33fe.c does.
> 
> Since the info in the ACPI tables for devices which use this
> driver is pretty terrible, we add a bunch of properties to notify
> the drivers about how the different parts which make up the Type-C
> functionality are tied together.
> 
> device_add_properties creates a new fwnode and then calls
> set_secondary_fwnode. For devices which already have a fwnode
> assigned (which the i2c-clients will have after this patch)
> set_secondary_fwnode sets dev->fwnode->secondary to the fwnode
> which has been newly created to hold the added properties.
> 
> Since all i2c-clients instantiated now share dev->fwnode,
> the result of this is that all i2c-clients created now will
> have the properties of the last i2c-client instantiated for
> an acpi-node which describes multiple clients in a single
> node.
> 
> Also the fwnodes created  for the properties of earlier
> instantiated i2c-clients will be leaked.

Thanks for this very detailed problem report.

> 
> I see 2 possible solutions here:
> 
> 1) Changing this patch so that i2c_acpi_new_device() does:
> 
>         /*
>          * The fwnode can not be shared between instantiated clients when
>          * adding device-properties to the instantiated client.
>          */
> 	if (!info->properties)
> 		info->fwnode = acpi_fwnode_handle(adev);
> 
> 2) Leave whether info->fwnode should be set or not up to the
> caller of i2c_acpi_new_device() (info is already passed in as
> a param). E.g. i2c-multi-instantiate.c could do this (for now,
> maybe in the future we will also want to add properties for
> some HIDs).
> 
> I think that 1. is the best solution and this is all kernel internal,
> so we can always revisit this if necessary.

Heikki told me he has some ideas, but for now I will drop this patch.


-- 
With Best Regards,
Andy Shevchenko