linux-kernel - Re: [PATCH v4 11/11] platform/x86: int3472: Deal with probe ordering issues

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Date:   Mon, 25 Oct 2021 14:40:39 +0300
From:   Andy Shevchenko <andy.shevchenko@...il.com>
To:     Hans de Goede <hdegoede@...hat.com>
Cc:     "Rafael J . Wysocki" <rjw@...ysocki.net>,
        Mark Gross <markgross@...nel.org>,
        Andy Shevchenko <andy@...radead.org>,
        Wolfram Sang <wsa@...-dreams.de>,
        Mika Westerberg <mika.westerberg@...ux.intel.com>,
        Daniel Scally <djrscally@...il.com>,
        Laurent Pinchart <laurent.pinchart@...asonboard.com>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        Liam Girdwood <lgirdwood@...il.com>,
        Mark Brown <broonie@...nel.org>,
        Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...nel.org>, Len Brown <lenb@...nel.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Platform Driver <platform-driver-x86@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linux-i2c <linux-i2c@...r.kernel.org>,
        Sakari Ailus <sakari.ailus@...ux.intel.com>,
        Kate Hsuan <hpa@...hat.com>,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        linux-clk <linux-clk@...r.kernel.org>
Subject: Re: [PATCH v4 11/11] platform/x86: int3472: Deal with probe ordering issues

On Mon, Oct 25, 2021 at 12:42 PM Hans de Goede <hdegoede@...hat.com> wrote:
>
> The clk and regulator frameworks expect clk/regulator consumer-devices
> to have info about the consumed clks/regulators described in the device's
> fw_node.
>
> To work around this info missing from the ACPI tables on devices where
> the int3472 driver is used, the int3472 MFD-cell drivers attach info about
> consumers to the clks/regulators when registering these.
>
> This causes problems with the probe ordering wrt drivers for consumers
> of these clks/regulators. Since the lookups are only registered when the
> provider-driver binds, trying to get these clks/regulators before then
> results in a -ENOENT error for clks and a dummy regulator for regulators.
>
> All the sensor ACPI fw-nodes have a _DEP dependency on the INT3472 ACPI
> fw-node, so to work around these probe ordering issues the ACPI core /
> i2c-code does not instantiate the I2C-clients for any ACPI devices
> which have a _DEP dependency on an INT3472 ACPI device until all
> _DEP-s are met.
>
> This relies on acpi_dev_clear_dependencies() getting called by the driver
> for the _DEP-s when they are ready, add a acpi_dev_clear_dependencies()
> call to the discrete.c probe code.
>
> In the tps68470 case calling acpi_dev_clear_dependencies() is already done
> by the acpi_gpiochip_add() call done by the driver for the GPIO MFD cell
> (The GPIO cell is deliberately the last cell created to make sure the
> clk + regulator cells are already instantiated when this happens).
>
> However for proper probe ordering, the clk/regulator cells must not just
> be instantiated the must be fully ready (the clks + regulators must be
> registered with their subsystems).
>
> Add MODULE_SOFTDEP dependencies for the clk and regulator drivers for
> the instantiated MFD-cells so that these are loaded before us and so
> that they bind immediately when the platform-devs are instantiated.

Just a side note: MODULE_SOFTDEP() won't work in some (special?) cases
when module tools are limited in functionality (e.g. busybox
implementation as of today).

-- 
With Best Regards,
Andy Shevchenko