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

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Message-ID: <CAAObsKBSKvR=1VPU7-E89my76FYbjVp7uDNsD2PGiVDJe89r1g@mail.gmail.com>
Date:	Fri, 31 Jul 2015 12:06:38 +0200
From:	Tomeu Vizoso <tomeu.vizoso@...labora.com>
To:	Rob Herring <robherring2@...il.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 30 July 2015 at 05:20, Rob Herring <robherring2@...il.com> wrote:
> 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.

I see no problem with restricting this to platform devices with an
of_node (or a fwnode if we still want to address machines with ACPI).

> 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.

Yeah, I'm not sure how much that could be a problem. Maybe if a
non-platform device has a match and probes before a platform device
that has been delayed and is a dependency of it. That could be a
problem in platforms that don't do on-demand probing because of the
lack of firmware data.

Thanks,

Tomeu

> Rob
> --
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