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From: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>
To: Johan Hovold <johan@kernel.org>
Cc: Jacopo Mondi <jacopo@jmondi.org>,
	linuxarm@huawei.com, mauro.chehab@huawei.com,
	Hans Verkuil <hverkuil-cisco@xs4all.nl>,
	Jacopo Mondi <jacopo+renesas@jmondi.org>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	linux-kernel@vger.kernel.org, linux-media@vger.kernel.org
Subject: Re: [PATCH 38/78] media: i2c: mt9m001: use pm_runtime_resume_and_get()
Date: Mon, 26 Apr 2021 16:38:40 +0200	[thread overview]
Message-ID: <20210426163840.67ea8af9@coco.lan> (raw)
In-Reply-To: <YIPsTsEA/F+o7fhQ@hovoldconsulting.com>

Em Sat, 24 Apr 2021 12:00:46 +0200
Johan Hovold <johan@kernel.org> escreveu:

> On Sat, Apr 24, 2021 at 10:24:54AM +0200, Jacopo Mondi wrote:
> > Hi Mauro,
> > 
> > On Sat, Apr 24, 2021 at 08:44:48AM +0200, Mauro Carvalho Chehab wrote:  
> > > Commit dd8088d5a896 ("PM: runtime: Add pm_runtime_resume_and_get to deal with usage counter")
> > > added pm_runtime_resume_and_get() in order to automatically handle
> > > dev->power.usage_count decrement on errors.
> > >
> > > Use the new API, in order to cleanup the error check logic.
> > >
> > > Signed-off-by: Mauro Carvalho Chehab <mchehab+huawei@kernel.org>  
> > 
> > Thanks
> > Acked-by: Jacopo Mondi <jacopo@jmondi.org>
> > 
> > I should re-work the error handling sequence there on top of this
> > patch as right now it's not the best, that 'done' label bothers me...
> > anyway, for later.
> >   
> > > ---
> > >  drivers/media/i2c/mt9m001.c | 7 ++++---
> > >  1 file changed, 4 insertions(+), 3 deletions(-)
> > >
> > > diff --git a/drivers/media/i2c/mt9m001.c b/drivers/media/i2c/mt9m001.c
> > > index 3b0ba8ed5233..57e15a291ebd 100644
> > > --- a/drivers/media/i2c/mt9m001.c
> > > +++ b/drivers/media/i2c/mt9m001.c
> > > @@ -217,9 +217,9 @@ static int mt9m001_s_stream(struct v4l2_subdev *sd, int enable)
> > >  		goto done;
> > >
> > >  	if (enable) {
> > > -		ret = pm_runtime_get_sync(&client->dev);
> > > +		ret = pm_runtime_resume_and_get(&client->dev);
> > >  		if (ret < 0)
> > > -			goto put_unlock;
> > > +			goto unlock;
> > >
> > >  		ret = mt9m001_apply_selection(sd);
> > >  		if (ret)
> > > @@ -247,6 +247,7 @@ static int mt9m001_s_stream(struct v4l2_subdev *sd, int enable)
> > >
> > >  put_unlock:
> > >  	pm_runtime_put(&client->dev);
> > > +unlock:
> > >  	mutex_unlock(&mt9m001->mutex);
> > >
> > >  	return ret;
> > > @@ -834,7 +835,7 @@ static int mt9m001_remove(struct i2c_client *client)
> > >  {
> > >  	struct mt9m001 *mt9m001 = to_mt9m001(client);
> > >
> > > -	pm_runtime_get_sync(&client->dev);
> > > +	pm_runtime_resume_and_get(&client->dev);
> > >
> > >  	v4l2_async_unregister_subdev(&mt9m001->subdev);
> > >  	media_entity_cleanup(&mt9m001->subdev.entity);  
> 
> I couldn't help looking at one more now that you got feedback on this
> one.
> 
> Here you have the same problem as the one I reported earlier, in that
> the usage count could end up negative on resume failure due to the later
> put_noidle() call in remove().

I'll double-check this at the entire series. Different sensor
drivers are handling this on different ways, which sounds
bad, as they are meant to be independent on the media bridge
driver.

> Also note that you're adding more lines than you're removing.

Ok, but the end goal is not really reducing the number of lines,
but to have the code following the same pattern, and to avoid
cut-and-paste errors when new drivers are written.

The mt9m001 is one of the oldest sensor drivers, written a long time
before the PM runtime core, written for the soc_camera driver, back
in 2008. The port to use PM runtime isn't old:

  commit 8fcfc491c6ca5887bb341b3a622cca3ed8e3c9f0
  Author: Akinobu Mita <akinobu.mita@gmail.com>
  Date:   Tue Jan 8 12:51:44 2019 -0200

    media: mt9m001: switch s_power callback to runtime PM

It was part of an attempt to recover the soc_camera sensor drives
from staging. 

Yet, the logic on this driver seems to be different than the
one used on more modern I2C sensors. So, better to re-check
everything.

> I'd say this kind of mass-conversion is of questionable worth as
> pm_runtime_resume_and_get() isn't necessarily an improvement (even if it
> may have its use in some places).

The main problem is that other parts of the driver's core APIs
assume that get object methods will only increment the usage
counter if no errors. The pm_runtime_get_sync() is an exception.

Its name doesn't help at all: A function like that should, IMHO,
be called, instead:

	pm_runtime_inc_usage_count_and_try_to_resume().

Or something similar, in order to make clearer that it always
increment the usage count, no matter what. If possible, all drivers
should get rid of it too (or alternatively add comments warning
people that keeping the usage_count incremented is desired on the
very specific places where it is really needed), as it is risky
to use something that has a different usage_count increement behavior
than other more usual *_get() functions.

With regards to mass-fixing it, I've seen several patches seen
to media fixing bugs due to the bad usage_count decrement logic.
So, the best is to solve them all at once, and stop using
pm_runtime_get_sync() inside the subsystem.

Thanks,
Mauro

  reply	other threads:[~2021-04-26 14:38 UTC|newest]

Thread overview: 127+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-04-24  6:44 [PATCH 00/78] media: use pm_runtime_resume_and_get() instead of pm_runtime_get_sync() Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 01/78] media: atmel: properly get pm_runtime Mauro Carvalho Chehab
2021-04-24  9:36   ` kernel test robot
2021-04-24  6:44 ` [PATCH 02/78] media: marvel-ccic: fix some issues when getting pm_runtime Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 03/78] media: mdk-mdp: fix pm_runtime_get_sync() usage count Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 04/78] media: rcar_fdp1: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 05/78] media: mdk-mdp: " Mauro Carvalho Chehab
2021-04-24 18:23   ` Ezequiel Garcia
2021-04-24  6:44 ` [PATCH 06/78] media: renesas-ceu: " Mauro Carvalho Chehab
2021-04-24  8:11   ` Jacopo Mondi
2021-04-24  6:44 ` [PATCH 07/78] media: s5p: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 08/78] media: am437x:: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 09/78] media: sh_vou: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 10/78] media: sti/hva: use pm_runtime_resume_and_get() Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 11/78] staging: media: rkvdec: fix pm_runtime_get_sync() usage count Mauro Carvalho Chehab
2021-04-24 23:20   ` Ezequiel Garcia
2021-04-24  6:44 ` [PATCH 12/78] staging: media: atomisp_fops: use pm_runtime_resume_and_get() Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 13/78] staging: media: hantro_drv: " Mauro Carvalho Chehab
2021-04-24 23:23   ` Ezequiel Garcia
2021-04-26 12:33     ` Mauro Carvalho Chehab
2021-04-26 12:42       ` Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 14/78] staging: media: imx7-mipi-csis: " Mauro Carvalho Chehab
2021-04-26 10:11   ` Rui Miguel Silva
2021-04-24  6:44 ` [PATCH 15/78] staging: media: ipu3: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 16/78] staging: media: cedrus_video: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 17/78] staging: media: vde: " Mauro Carvalho Chehab
2021-04-24  7:35   ` Dmitry Osipenko
2021-04-27  9:22     ` Mauro Carvalho Chehab
2021-04-27 12:34       ` Johan Hovold
2021-04-24  6:44 ` [PATCH 18/78] staging: media: csi: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 19/78] staging: media: vi: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 20/78] media: mtk-vcodec: fix pm_runtime_get_sync() usage count Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 21/78] media: s5p-jpeg: " Mauro Carvalho Chehab
2021-04-27  9:14   ` Sylwester Nawrocki
2021-04-24  6:44 ` [PATCH 22/78] media: delta-v4l2: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 23/78] media: sun8i_rotate: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 24/78] media: i2c: ak7375: use pm_runtime_resume_and_get() Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 25/78] media: i2c: ccs-core: " Mauro Carvalho Chehab
2021-04-25 18:55   ` Sakari Ailus
2021-04-26 14:01     ` Mauro Carvalho Chehab
2021-04-26 14:09       ` Sakari Ailus
2021-04-26 14:16         ` Mauro Carvalho Chehab
2021-04-26 14:29           ` Sakari Ailus
2021-04-26 17:32             ` Mauro Carvalho Chehab
2021-04-27  7:02               ` Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 26/78] media: i2c: dw9714: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 27/78] media: i2c: dw9768: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 28/78] media: i2c: dw9807-vcm: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 29/78] media: i2c: hi556: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 30/78] media: i2c: imx214: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 31/78] media: i2c: imx219: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 32/78] media: i2c: imx258: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 33/78] media: i2c: imx274: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 34/78] media: i2c: imx290: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 35/78] media: i2c: imx319: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 36/78] media: i2c: imx334: " Mauro Carvalho Chehab
2021-04-26  9:06   ` Alessandrelli, Daniele
2021-04-24  6:44 ` [PATCH 37/78] media: i2c: imx355: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 38/78] media: i2c: mt9m001: " Mauro Carvalho Chehab
2021-04-24  8:24   ` Jacopo Mondi
2021-04-24 10:00     ` Johan Hovold
2021-04-26 14:38       ` Mauro Carvalho Chehab [this message]
2021-04-27 12:23         ` Johan Hovold
2021-04-28  8:31           ` Mauro Carvalho Chehab
2021-04-28 10:05             ` Johan Hovold
2021-04-28 11:28               ` Mauro Carvalho Chehab
2021-04-28 11:56                 ` Johan Hovold
2021-04-24  6:44 ` [PATCH 39/78] media: i2c: ov02a10: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 40/78] media: i2c: ov13858: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 41/78] media: i2c: ov2659: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 42/78] media: i2c: ov2685: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 43/78] media: i2c: ov2740: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 44/78] media: i2c: ov5647: " Mauro Carvalho Chehab
2021-04-24  8:30   ` Jacopo Mondi
2021-04-24  6:44 ` [PATCH 45/78] media: i2c: ov5648: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 46/78] media: i2c: ov5670: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 47/78] media: i2c: ov5675: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 48/78] media: i2c: ov5695: " Mauro Carvalho Chehab
2021-04-24  6:44 ` [PATCH 49/78] media: i2c: ov7740: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 50/78] media: i2c: ov8856: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 51/78] media: i2c: ov8865: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 52/78] media: i2c: ov9734: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 53/78] media: i2c: tvp5150: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 54/78] media: i2c: video-i2c: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 55/78] media: ipu3: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 56/78] media: coda: " Mauro Carvalho Chehab
2021-04-26  6:53   ` Philipp Zabel
2021-04-24  6:45 ` [PATCH 57/78] media: exynos4-is: " Mauro Carvalho Chehab
2021-04-25 20:57   ` Sylwester Nawrocki
2021-04-26 13:12     ` Mauro Carvalho Chehab
2021-04-27  8:06       ` Sylwester Nawrocki
2021-04-24  6:45 ` [PATCH 58/78] media: exynos-gsc: " Mauro Carvalho Chehab
2021-04-27  8:18   ` Sylwester Nawrocki
2021-04-27  9:30     ` Mauro Carvalho Chehab
2021-04-27  9:42       ` Mauro Carvalho Chehab
2021-04-27 11:50         ` Sylwester Nawrocki
2021-04-28  7:13           ` Mauro Carvalho Chehab
2021-04-28  7:17             ` Mauro Carvalho Chehab
2021-04-28  8:27               ` Sylwester Nawrocki
2021-04-24  6:45 ` [PATCH 59/78] media: mtk-jpeg: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 60/78] media: camss-csid: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 61/78] media: camss-csiphy: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 62/78] media: camss-ispif: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 63/78] media: camss-vfe: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 64/78] media: core: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 65/78] media: pm_helpers: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 66/78] media: vdec: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 67/78] media: venc: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 68/78] media: rcar-fcp: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 69/78] media: rcar-vin: " Mauro Carvalho Chehab
2021-04-24  8:33   ` Niklas Söderlund
2021-04-24  9:12   ` Geert Uytterhoeven
2021-04-26 13:33     ` Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 70/78] media: rga-buf: " Mauro Carvalho Chehab
2021-04-28 17:09   ` Ezequiel Garcia
2021-04-24  6:45 ` [PATCH 71/78] media: rkisp1-capture: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 72/78] media: s3c-camif: " Mauro Carvalho Chehab
2021-04-25 19:36   ` Sylwester Nawrocki
2021-04-24  6:45 ` [PATCH 73/78] media: s5p-mfc: " Mauro Carvalho Chehab
2021-04-27  9:36   ` Sylwester Nawrocki
2021-04-24  6:45 ` [PATCH 74/78] media: bdisp-v4l2: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 75/78] media: stm32: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 76/78] media: sun4i_v4l2: " Mauro Carvalho Chehab
2021-04-24 10:21   ` kernel test robot
2021-04-24  6:45 ` [PATCH 77/78] media: ti-vpe: " Mauro Carvalho Chehab
2021-04-24  6:45 ` [PATCH 78/78] media: vsp1: " Mauro Carvalho Chehab
2021-04-28 10:13 ` [PATCH 00/78] media: use pm_runtime_resume_and_get() instead of pm_runtime_get_sync() Dan Carpenter

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