linux-kernel - Re: [PATCH v2 01/22] platform: delay device-driver matches until late

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Date:	Wed, 29 Jul 2015 22:20:05 -0500
From:	Rob Herring <robherring2@...il.com>
To:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
Cc:	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-acpi@...r.kernel.org" <linux-acpi@...r.kernel.org>,
	Arnd Bergmann <arnd@...db.de>,
	Stephen Warren <swarren@...dotorg.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Linus Walleij <linus.walleij@...aro.org>,
	Dmitry Torokhov <dmitry.torokhov@...il.com>,
	"Rafael J. Wysocki" <rjw@...ysocki.net>,
	Javier Martinez Canillas <javier@....samsung.com>,
	Mark Brown <broonie@...nel.org>,
	Thierry Reding <thierry.reding@...il.com>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 01/22] platform: delay device-driver matches until late_initcall

On Tue, Jul 28, 2015 at 8:19 AM, Tomeu Vizoso
<tomeu.vizoso@...labora.com> wrote:
> Delay matches of platform devices until late_initcall, when we are sure
> that all built-in drivers have been registered already.  This is needed
> to prevent deferred probes because of some drivers not having registered
> yet.
>
> The reason why only platform devices are delayed is that some other
> devices are expected to be probed earlier than late_initcall, for
> example, the system PNP driver needs to probe its devices in
> fs_initcall.
>
> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
> ---
>
> Changes in v2:
> - Move delay to platform.c
>
>  drivers/base/platform.c | 28 ++++++++++++++++++++++++++++
>  1 file changed, 28 insertions(+)
>
> diff --git a/drivers/base/platform.c b/drivers/base/platform.c
> index 063f0ab15259..fcf654678e27 100644
> --- a/drivers/base/platform.c
> +++ b/drivers/base/platform.c
> @@ -33,6 +33,8 @@
>  /* For automatically allocated device IDs */
>  static DEFINE_IDA(platform_devid_ida);
>
> +static bool enable_matches;
> +
>  struct device platform_bus = {
>         .init_name      = "platform",
>  };
> @@ -839,6 +841,15 @@ static int platform_match(struct device *dev, struct device_driver *drv)
>         struct platform_device *pdev = to_platform_device(dev);
>         struct platform_driver *pdrv = to_platform_driver(drv);
>
> +       /*
> +        * Delay matches of platform devices until late_initcall, when we are
> +        * sure that all built-in drivers have been registered already. This
> +        * is needed to prevent deferred probes because of some drivers
> +        * not having registered yet.
> +        */
> +       if (!enable_matches)
> +               return false;
> +

Having this as a global makes me nervous. I think it would be better
to be DT specific or per device some how. Perhaps use OF_POPULATED_BUS
flag as an additional test.

There could be non-DT platforms that rely on the initcall ordering and
moving all probes to late_initcall could change the ordering. I'm not
sure though.

Rob
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