linux-kernel - Re: [RFC PATCH v3] drivercore: Add driver probe deferral mechanism

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Date:	Wed, 5 Oct 2011 00:05:16 +0530
From:	"G, Manjunath Kondaiah" <manjugk@...com>
To:	Grant Likely <grant.likely@...retlab.ca>
Cc:	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	Greg Kroah-Hartman <greg@...ah.com>,
	Dilan Lee <dilee@...dia.com>,
	Mark Brown <broonie@...nsource.wolfsonmicro.com>,
	Manjunath GKondaiah <manjunath.gkondaiah@...aro.org>,
	Arnd Bergmann <arnd@...db.de>, linux-omap@...r.kernel.org
Subject: Re: [RFC PATCH v3] drivercore: Add driver probe deferral mechanism

On Tue, Oct 04, 2011 at 09:58:10AM -0600, Grant Likely wrote:
> On Tue, Oct 4, 2011 at 8:51 AM, G, Manjunath Kondaiah <manjugk@...com> wrote:
> > On Thu, Sep 22, 2011 at 12:51:23PM -0600, Grant Likely wrote:
> >> Hi Manjunath,
> >>
> >> Here's the current state of the patch.  The major think that needs to
> >> be done is to convert it to use a separate workqueue as described in
> >> the TODO above.  It also needs some users adapted to it.  One of the
> >> gpio drivers would work; preferably one of the newer drivers that
> >> doesn't have a lot of drivers depending on the early_initcall()
> >> behaviour yet.
> >
> > I have tested this patch on omap3 beagle board by making:
> > 1. omap-gpio driver init as late_initcall instead of postcore_initcall
> > 2. mmc driver probe will request gpio through gpio_request and gpio driver
> > returns -EDEFER_PROBE which in turn makes mmc driver to request deferral probe.
> > 3. When deferral probe gets activated, it scans driver entries and it will not
> > find any match for mmc driver probe.
> 
> Looks like drivers/mmc/host/omap.c is using platform_driver_probe()
> instead of platform_driver_register().  Add the probe hook to the
> platform_driver structure and change it to call
> platform_driver_register() and it should work.  Don't forget to change
> mmc_omap_probe from __init to __devinit.

Yes. After changing it into platform_driver_register, I can see mmc probe is
getting completed from deferred probe list. But, MMC upper layer will check 
probe and it waits for ever since probe_count is not getting incremented.

Log:

[    1.807830] platform omap_hsmmc.0: Driver omap_hsmmc requests probe deferral

...

[    1.948760] omap_device: omap_gpio.0: new worst case activate latency 0:30517
[    1.959259] OMAP GPIO hardware version 2.5

...

[    2.000488] platform omap_hsmmc.0: Retrying from deferred list
[    2.008026] omap_device: omap_hsmmc.0: new worst case activate latency 0:244140
[    2.020080] input: gpio-keys as /devices/platform/gpio-keys/input/input1
[    2.035827] omap_hsmmc omap_hsmmc.0: Probe success...
[    2.042083] twl_rtc twl_rtc: setting system clock to 2000-01-01 01:06:35 UTC
(946688795)
[    2.056030] Waiting for root device /dev/mmcblk0p2...
[    2.061492] driver_probe_done: probe_count = 0
[    2.168518] driver_probe_done: probe_count = 0
[    2.277832] driver_probe_done: probe_count = 0
[    2.387207] driver_probe_done: probe_count = 0
[    2.496582] driver_probe_done: probe_count = 0

Waits for ever in init/do_mount.c:
	if ((ROOT_DEV == 0) && root_wait) {
		printk(KERN_INFO "Waiting for root device %s...\n",
			saved_root_name);
		while (driver_probe_done() != 0 ||
			(ROOT_DEV = name_to_dev_t(saved_root_name)) == 0)
			msleep(100);
		async_synchronize_full();
	}

-Manjunath
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