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From: Boris Brezillon <boris.brezillon@free-electrons.com>
To: Mark Brown <broonie@kernel.org>
Cc: Thierry Reding <thierry.reding@gmail.com>,
	linux-pwm@vger.kernel.org,
	Mike Turquette <mturquette@baylibre.com>,
	Stephen Boyd <sboyd@codeaurora.org>,
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	Stephen Barber <smbarber@chromium.org>
Subject: Re: [PATCH v5 30/46] regulator: pwm: retrieve correct voltage
Date: Thu, 7 Apr 2016 23:54:31 +0200	[thread overview]
Message-ID: <20160407235431.788dc24a@bbrezillon> (raw)
In-Reply-To: <20160330212410.GX2350@sirena.org.uk>

Hi Mark,

On Wed, 30 Mar 2016 14:24:10 -0700
Mark Brown <broonie@kernel.org> wrote:

> On Wed, Mar 30, 2016 at 10:03:53PM +0200, Boris Brezillon wrote:
> > The continuous PWM voltage regulator is caching the voltage value in
> > the ->volt_uV field. While most of the time this value should reflect the
> > real voltage, sometime it can be sightly different if the PWM device
> > rounded the set_duty_cycle request.
> > Moreover, this value is not valid until someone has modified the regulator
> > output.
> 
> Acked-by: Mark Brown <broonie@kernel.org>

Actually this patch introduces a bug (reported by Stephen):

"
I applied your patch series [PATCH v5 00/46] pwm: add support for
atomic update and found a null pointer dereference when probing a
pwm-regulator at boot. See the below stack trace:

[ 4.282374] [<ffffffc000399088>] pwm_regulator_get_voltage+0x78/0xa0
[ 4.289344] [<ffffffc000390740>] regulator_attr_is_visible+0x7c/0x264
[ 4.296408] [<ffffffc0001f75a0>] internal_create_group+0x14c/0x280
[ 4.303184] [<ffffffc0001f76e8>] sysfs_create_group+0x14/0x1c
[ 4.309483] [<ffffffc0001f77c8>] sysfs_create_groups+0x30/0x78
[ 4.315881] [<ffffffc00043631c>] device_add+0x224/0x4d8
[ 4.321609] [<ffffffc0004365ec>] device_register+0x1c/0x28
[ 4.327623] [<ffffffc0003952a4>] regulator_register+0x2e4/0xc14
[ 4.334112] [<ffffffc000396844>] devm_regulator_register+0x54/0x94
[ 4.340887] [<ffffffc000399328>] pwm_regulator_probe+0x278/0x2b8
[ 4.347473] [<ffffffc000439fe4>] platform_drv_probe+0x58/0xa4
[ 4.353772] [<ffffffc0004387a8>] driver_probe_device+0x114/0x2ac
[ 4.360358] [<ffffffc0004389a4>] __driver_attach+0x64/0x90
[ 4.366371] [<ffffffc000436f50>] bus_for_each_dev+0x74/0x90
[ 4.372478] [<ffffffc000438bd4>] driver_attach+0x20/0x28
[ 4.378299] [<ffffffc00043778c>] bus_add_driver+0xe8/0x1e0
[ 4.384312] [<ffffffc00043959c>] driver_register+0x98/0xe4
[ 4.390326] [<ffffffc00043aa04>] __platform_driver_register+0x48/0x50
[ 4.397388] [<ffffffc000cb2710>] pwm_regulator_driver_init+0x18/0x20
[ 4.404356] [<ffffffc000c8ca7c>] do_one_initcall+0xf8/0x180
[ 4.410466] [<ffffffc000c8cc58>] kernel_init_freeable+0x154/0x1f4
[ 4.417148] [<ffffffc000929cf4>] kernel_init+0x10/0xf8
[ 4.422782] [<ffffffc000084450>] ret_from_fork+0x10/0x40

It looks like the root cause is that regulator_attr_is_visible will
try to get the voltage, but at this point in regulator_register,
rdev->constraints is still null. So
pwm_duty_cycle_percentage_to_voltage will dereference a null
rdev->constraints pointer.
"

The problem is that we need to know the min and max voltage constraints
to calculate the current voltage. ->get_voltage() is called when the
sysfs attributes are created (part of device registration), and
set_machine_constraints() is called after device_register(), thus
leading to the NULL pointer dereference.

Is there any reason for calling set_machine_constraints() after
device_register() in regulator_register()?

Best Regards,

Boris

  reply	other threads:[~2016-04-07 21:54 UTC|newest]

Thread overview: 105+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2016-03-30 20:03 [PATCH v5 00/46] pwm: add support for atomic update Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 01/46] pwm: rcar: make use of pwm_is_enabled() Boris Brezillon
2016-04-12 11:01   ` Thierry Reding
2016-04-14 11:05     ` Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 02/46] backlight: pwm_bl: remove useless call to pwm_set_period() Boris Brezillon
2016-04-12 11:03   ` Thierry Reding
2016-04-12 14:16     ` Lee Jones
2016-04-12 14:25       ` Thierry Reding
2016-03-30 20:03 ` [PATCH v5 03/46] backlight: lm3630a_bl: stop messing with the pwm->period field Boris Brezillon
2016-04-12 11:08   ` Thierry Reding
2016-04-12 14:16     ` Lee Jones
2016-04-12 14:26       ` Thierry Reding
2016-04-13  8:25         ` Lee Jones
2016-04-13  8:26           ` Lee Jones
2016-03-30 20:03 ` [PATCH v5 04/46] pwm: get rid of pwm->lock Boris Brezillon
2016-04-12 11:22   ` Thierry Reding
2016-04-12 11:32     ` Boris Brezillon
2016-04-12 11:46       ` Thierry Reding
2016-03-30 20:03 ` [PATCH v5 05/46] pwm: introduce the pwm_args concept Boris Brezillon
2016-03-30 21:55   ` Stephen Boyd
2016-03-31  7:09     ` Boris Brezillon
2016-03-31  7:57     ` Boris Brezillon
2016-04-12 11:39   ` Thierry Reding
2016-04-12 12:04     ` Boris Brezillon
2016-04-12 12:20       ` Thierry Reding
2016-04-12 12:55         ` Boris Brezillon
2016-04-12 13:06     ` Boris Brezillon
2016-04-12 13:15       ` Thierry Reding
2016-03-30 20:03 ` [PATCH v5 06/46] pwm: use pwm_get/set_xxx() helpers where appropriate Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 07/46] clk: pwm: use pwm_get_args() " Boris Brezillon
2016-03-30 21:58   ` Stephen Boyd
2016-03-30 20:03 ` [PATCH v5 08/46] hwmon: pwm-fan: " Boris Brezillon
2016-03-30 22:52   ` Guenter Roeck
2016-03-31  7:07     ` Boris Brezillon
2016-04-04 15:20       ` Thierry Reding
2016-04-01  8:29   ` Kamil Debski
2016-03-30 20:03 ` [PATCH v5 09/46] misc: max77693-haptic: " Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 10/46] leds: pwm: " Boris Brezillon
2016-03-31  7:13   ` Jacek Anaszewski
2016-03-30 20:03 ` [PATCH v5 11/46] regulator: " Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 12/46] fbdev: ssd1307fb: " Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 13/46] backlight: pwm_bl: " Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 14/46] pwm: keep PWM state in sync with hardware state Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 15/46] pwm: introduce the pwm_state concept Boris Brezillon
2016-04-12 11:49   ` Thierry Reding
2016-04-12 12:17     ` Boris Brezillon
2016-04-12 12:21       ` Thierry Reding
2016-04-12 12:45         ` Boris Brezillon
2016-04-12 13:11           ` Thierry Reding
2016-04-12 13:26             ` Boris Brezillon
2016-04-12 14:05               ` Thierry Reding
2016-04-12 14:13                 ` Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 16/46] pwm: move the enabled/disabled info into pwm_state Boris Brezillon
2016-04-12 11:51   ` Thierry Reding
2016-03-30 20:03 ` [PATCH v5 17/46] pwm: add the PWM initial state retrieval infra Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 18/46] pwm: add the core infrastructure to allow atomic update Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 19/46] pwm: switch to the atomic API Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 20/46] pwm: add information about polarity, duty cycle and period to debugfs Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 21/46] pwm: rockchip: add initial state retrieval Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 22/46] pwm: rockchip: avoid glitches on already running PWMs Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 23/46] pwm: rockchip: add support for atomic update Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 24/46] pwm: sti: add support for initial state retrieval Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 25/46] pwm: sti: avoid glitches on already running PWMs Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 26/46] pwm: sun4i: implement hardware readout Boris Brezillon
2016-03-31  8:00   ` Alexandre Belloni
2016-03-30 20:03 ` [PATCH v5 27/46] regulator: pwm: adjust PWM config at probe time Boris Brezillon
2016-03-30 21:22   ` Mark Brown
2016-03-30 20:03 ` [PATCH v5 28/46] regulator: pwm: swith to the atomic PWM API Boris Brezillon
2016-03-30 21:23   ` Mark Brown
2016-03-30 20:03 ` [PATCH v5 29/46] regulator: pwm: properly initialize the ->state field Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 30/46] regulator: pwm: retrieve correct voltage Boris Brezillon
2016-03-30 21:24   ` Mark Brown
2016-04-07 21:54     ` Boris Brezillon [this message]
2016-04-12  4:42       ` Mark Brown
2016-04-12  8:37         ` Boris Brezillon
2016-04-12 10:09           ` Mark Brown
2016-04-12 10:31             ` Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 31/46] pwm: update documentation Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 32/46] pwm: deprecate pwm_config(), pwm_enable() and pwm_disable() Boris Brezillon
2016-03-31 17:38   ` Dmitry Torokhov
2016-03-31 18:54     ` Boris Brezillon
2016-04-04 15:22       ` Thierry Reding
2016-03-30 20:03 ` [PATCH v5 33/46] pwm: replace pwm_disable() by pwm_apply_state() Boris Brezillon
2016-03-30 20:03 ` [PATCH v5 34/46] clk: pwm: switch to the atomic API Boris Brezillon
2016-03-30 22:01   ` Stephen Boyd
2016-03-31  6:57     ` Boris Brezillon
2016-04-04 15:30       ` Thierry Reding
2016-03-30 20:03 ` [PATCH v5 35/46] hwmon: pwm-fan: " Boris Brezillon
2016-04-01  8:29   ` Kamil Debski
2016-03-30 20:03 ` [PATCH v5 36/46] input: misc: max77693: " Boris Brezillon
2016-03-31 17:48   ` Dmitry Torokhov
2016-03-31 18:57     ` Boris Brezillon
2016-04-04 15:34       ` Thierry Reding
2016-03-30 20:04 ` [PATCH v5 37/46] input: misc: max8997: switch to the atomic PWM API Boris Brezillon
2016-03-30 20:04 ` [PATCH v5 38/46] input: misc: pwm-beeper: " Boris Brezillon
2016-03-30 20:04 ` [PATCH v5 39/46] leds: pwm: " Boris Brezillon
2016-03-30 20:04 ` [PATCH v5 40/46] backlight: lm3630a: " Boris Brezillon
2016-03-30 20:04 ` [PATCH v5 41/46] backlight: lp855x: " Boris Brezillon
2016-03-30 20:04 ` [PATCH v5 42/46] backlight: lp8788: " Boris Brezillon
2016-03-30 20:04 ` [PATCH v5 43/46] backlight: pwm_bl: " Boris Brezillon
2016-03-30 20:04 ` [PATCH v5 44/46] video: ssd1307fb: " Boris Brezillon
2016-03-30 20:04 ` [PATCH v5 45/46] drm: i915: " Boris Brezillon
2016-03-30 20:04 ` [PATCH v5 46/46] ARM: s3c24xx: rx1950: " Boris Brezillon
2016-03-30 20:18 ` [PATCH v5 00/46] pwm: add support for atomic update Boris Brezillon
2016-04-11 22:42 ` Boris Brezillon

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