Hi Laurent,

On Thu, Jul 08, 2021 at 12:51:16AM +0300, Laurent Pinchart wrote:

Hi Sakari,

On Thu, Jul 08, 2021 at 12:44:15AM +0300, Sakari Ailus wrote:

quoted

On Thu, Jul 08, 2021 at 12:00:57AM +0300, Laurent Pinchart wrote:

quoted

On Wed, Jul 07, 2021 at 11:37:18PM +0300, Sakari Ailus wrote:

quoted

On Fri, Jun 25, 2021 at 12:51:50AM +0530, Pratyush Yadav wrote:

quoted

Calling s_power subdev callback is discouraged. Instead, the subdevs
should use runtime PM to control its power. Use runtime PM callbacks to
control sensor power. The pm counter is incremented when the stream is
started and decremented when the stream is stopped.

Refactor s_stream() a bit to make this new control flow easier. Add a
helper to choose whether mipi or dvp set_stream needs to be called. The
logic flow is also changed to make it a bit clearer.

Signed-off-by: Pratyush Yadav <redacted>

---

Changes in v3:
- Clean up the logic in ov5640_s_stream() a bit.
- Use pm_runtime_resume_and_get() instead of pm_runtime_get_sync().
- Rename the label error_pm to disable_pm.

Changes in v2:
- New in v2.

 drivers/media/i2c/Kconfig  |   2 +-
 drivers/media/i2c/ov5640.c | 127 +++++++++++++++++++++++--------------
 2 files changed, 79 insertions(+), 50 deletions(-)

diff --git a/drivers/media/i2c/Kconfig b/drivers/media/i2c/Kconfig
index 588f8eb95984..8f43a4d7bcc1 100644
--- a/drivers/media/i2c/Kconfig
+++ b/drivers/media/i2c/Kconfig

@@ -929,7 +929,7 @@ config VIDEO_OV2740
 
 config VIDEO_OV5640
 	tristate "OmniVision OV5640 sensor support"
-	depends on OF
+	depends on OF && PM

Could you add support for runtime PM without requiring CONFIG_PM?

Essentially you'll need to power on the device in probe and power it off in
probe, and make sure the runtime PM nop variant functions return the value
you'd expect.

I've gone through that in several sensor drivers, and it really
increases the complexity to get it right, to a point where I'm not
comfortable asking someone to do the same (not to mention the very, very

I don't think it's very complicated, really. Looking at examples of other
drivers (e.g. imx334) doing exactly the same helps as you don't need to
check for individual functions.

The complexity of the power management in this driver is mostly because of
evolutionary development done over time, it's an old driver.

https://git.linuxtv.org/pinchartl/media.git/commit/?h=sensors/ar0330/driver&id=e72ca23c4c6b1ab6b06ac48280726e09d63cc818

Look at the changes to ar0330_probe(). As far as I understand, anything
less than that would be incorrect, and it's way too easy to get it
wrong.

The driver uses autosuspend that requires quite a few extra calls to
runtime PM framework. The only other driver doing this may be the CCS
driver.

quoted

quoted

high chance that it won't be done correctly). What's the practical
drawback in requiring CONFIG_PM ?

Good question. CONFIG_PM is something you can disable (for a reason I can't
think of though). Why should a driver depend on it when it could perfectly
work without it as well?

Because it requires additional complexity in the driver, times the
number of sensor drivers we have in the kernel. Not even mentioning test

How much of additional complexity?

You need to call the function powering on the sensor in probe, and call
another one to power the sensor off in remove, and make sure the use of
runtime PM functions is correct. Good examples exist of this.

Even if you fully relied on runtime PM and do not call the aforementioned
functions directly, you need to power on the sensor in probe using runtime
PM on DT based systems which is not the case on ACPI based systems. These
differences need to be taken into account in that case.

coverage, I'm pretty sure very few people would test the sensor drivers
without CONFIG_PM.

That is probably true.

-- 
Regards,

Sakari Ailus