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Message-ID: <CAAObsKBoBgP_y161qWC_U+yVtbWxudFgBNM7map0jz2WcJws_w@mail.gmail.com>
Date: Tue, 29 Sep 2015 10:05:38 +0200
From: Tomeu Vizoso <tomeu.vizoso@...labora.com>
To: Rob Herring <robh@...nel.org>
Cc: "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
Stephen Warren <swarren@...dotorg.org>,
Javier Martinez Canillas <javier@....samsung.com>,
Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
Mark Brown <broonie@...nel.org>,
Thierry Reding <thierry.reding@...il.com>,
Alan Stern <stern@...land.harvard.edu>,
"Rafael J. Wysocki" <rjw@...ysocki.net>,
"linux-arm-kernel@...ts.infradead.org"
<linux-arm-kernel@...ts.infradead.org>,
Dmitry Torokhov <dmitry.torokhov@...il.com>,
"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
Linus Walleij <linus.walleij@...aro.org>,
linux-acpi@...r.kernel.org, Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH v6 20/22] driver core: Allow deferring probes until late init
On 26 September 2015 at 20:15, Rob Herring <robh@...nel.org> wrote:
> On 09/21/2015 09:03 AM, Tomeu Vizoso wrote:
>> Add a field to struct device that instructs the device-driver core to
>> defer the probe of this device until the late_initcall level.
>
> This is true until the next patch with moves deferred probe processing
> to device_initcall_sync. So disabling this option alone won't totally
> revert to current behaviour. I guess patch 21 could be reverted if
> necessary.
Actually, the goal with that commit was to prevent potential problems
due to the increased pressure on late_initcall, as suggested by
Grygorii Strashko, but I haven't found yet any evidence of it being
needed, and in my testing the series boot all boards in kernelci with
or without this commit. So I would just not commit it for now and only
consider applying it later if someone reports a problem.
>> By letting all built-in drivers to register before starting to probe, we
>> can avoid any deferred probes by probing dependencies on demand.
>>
>> Signed-off-by: Tomeu Vizoso <tomeu.vizoso@...labora.com>
>>
>> ---
>>
>> Changes in v4:
>> - Add Kconfig DELAY_DEVICE_PROBES to allow disabling delayed probing in
>> machines with initcalls that depend on devices probing at a given time.
>>
>> drivers/base/Kconfig | 18 ++++++++++++++++++
>> drivers/base/dd.c | 7 +++++++
>> include/linux/device.h | 2 ++
>> 3 files changed, 27 insertions(+)
>>
>> diff --git a/drivers/base/Kconfig b/drivers/base/Kconfig
>> index 98504ec99c7d..44b5d33b1f49 100644
>> --- a/drivers/base/Kconfig
>> +++ b/drivers/base/Kconfig
>> @@ -324,4 +324,22 @@ config CMA_ALIGNMENT
>>
>> endif
>>
>> +config DELAY_DEVICE_PROBES
>> + bool "Allow delaying the probe of some devices"
>
> I'd like to hide visibility of this behind EXPERT.
Done.
>> + default y
>> + help
>> + Devices can be matched to a driver and probed from the moment they
>> + are registered, but early during boot their probes are likely to be
>> + deferred because some dependency isn't available yet because most
>> + drivers haven't been registered yet.
>> +
>> + Enabling this option allows the device registration code to delay the
>> + probing of a specific device until device_initcall_sync, when all
>> + built-in drivers have been registered already.
>> +
>> + In some platforms there may be implicit assumptions about when some
>> + devices are probed, so enabling this option could cause problems there.
>> +
>> + If unsure, say Y here.
>> +
>> endmenu
>> diff --git a/drivers/base/dd.c b/drivers/base/dd.c
>> index 7dc04ee81c8b..269ea76c1a4f 100644
>> --- a/drivers/base/dd.c
>> +++ b/drivers/base/dd.c
>> @@ -417,6 +417,13 @@ int driver_probe_device(struct device_driver *drv, struct device *dev)
>> if (!device_is_registered(dev))
>> return -ENODEV;
>>
>> +#if IS_ENABLED(CONFIG_DELAY_DEVICE_PROBES)
>
> This can be moved to the if.
Done.
Thanks,
Tomeu
>> + if (!driver_deferred_probe_enable && dev->probe_late) {
>> + driver_deferred_probe_add(dev);
>> + return 0;
>> + }
>> +#endif
>> +
>> pr_debug("bus: '%s': %s: matched device %s with driver %s\n",
>> drv->bus->name, __func__, dev_name(dev), drv->name);
>>
>> diff --git a/include/linux/device.h b/include/linux/device.h
>> index 8e7b806f0744..e64f4c7e243d 100644
>> --- a/include/linux/device.h
>> +++ b/include/linux/device.h
>> @@ -744,6 +744,7 @@ struct device_dma_parameters {
>> *
>> * @offline_disabled: If set, the device is permanently online.
>> * @offline: Set after successful invocation of bus type's .offline().
>> + * @probe_late: If set, device will be probed in the late initcall level.
>> *
>> * At the lowest level, every device in a Linux system is represented by an
>> * instance of struct device. The device structure contains the information
>> @@ -828,6 +829,7 @@ struct device {
>>
>> bool offline_disabled:1;
>> bool offline:1;
>> + bool probe_late:1;
>> };
>>
>> static inline struct device *kobj_to_dev(struct kobject *kobj)
>>
>
> --
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