[RFC/PATCH 09/13] media: s5k6aa: Add support for device tree based instantiation

[Guennadi Liakhovetski]

On Tue, 31 Jul 2012, Laurent Pinchart wrote:

> Hi Guennadi,
> 
> On Tuesday 31 July 2012 13:14:13 Guennadi Liakhovetski wrote:
> > On Tue, 31 Jul 2012, Laurent Pinchart wrote:
> > > On Tuesday 31 July 2012 11:56:44 Guennadi Liakhovetski wrote:
> > > > On Thu, 26 Jul 2012, Laurent Pinchart wrote:
> > > > > On Wednesday 18 July 2012 11:18:33 Sylwester Nawrocki wrote:
> > > > > > On 07/16/2012 11:42 AM, Guennadi Liakhovetski wrote:
> > > > > > > On Fri, 25 May 2012, Sylwester Nawrocki wrote:
> > > > > > >> The driver initializes all board related properties except the
> > > > > > >> s_power() callback to board code. The platforms that require this
> > > > > > >> callback are not supported by this driver yet for CONFIG_OF=y.
> > > > > > >> 
> > > > > > >> Signed-off-by: Sylwester Nawrocki<s.nawrocki at samsung.com>
> > > > > > >> Signed-off-by: Bartlomiej
> > > > > > >> Zolnierkiewicz<b.zolnierkie at samsung.com>
> > > > > > >> Signed-off-by: Kyungmin Park<kyungmin.park at samsung.com>
> > > > > > >> ---
> > > > > > >> 
> > > > > > >>   .../bindings/camera/samsung-s5k6aafx.txt           |   57
> > > > > > >>   +++++++++
> > > > > > >>   drivers/media/video/s5k6aa.c                       |  129
> > > > > > >>   ++++++++++++++------ 2 files changed, 146 insertions(+), 40
> > > > > > >>   deletions(-)
> > > > > > >>   create mode 100644
> > > > > > >>   Documentation/devicetree/bindings/camera/samsung-s5k6aafx.txt>>
> > > > > > >> 
> > > > > > >> diff --git
> > > > > > >> a/Documentation/devicetree/bindings/camera/samsung-s5k6aafx.txt
> > > > > > >> b/Documentation/devicetree/bindings/camera/samsung-s5k6aafx.txt
> > > > > > >> new
> > > > > > >> file
> > > > > > >> mode 100644
> > > > > > >> index 0000000..6685a9c
> > > > > > >> --- /dev/null
> > > > > > >> +++
> > > > > > >> b/Documentation/devicetree/bindings/camera/samsung-s5k6aafx.txt
> > > > > > >> @@ -0,0 +1,57 @@
> > > > > > >> +Samsung S5K6AAFX camera sensor
> > > > > > >> +------------------------------
> > > > > > >> +
> > > > > > >> +Required properties:
> > > > > > >> +
> > > > > > >> +- compatible : "samsung,s5k6aafx";
> > > > > > >> +- reg : base address of the device on I2C bus;
> > > > > > > 
> > > > > > > You said you ended up putting your sensors outside of I2C busses,
> > > > > > > is this one of changes, that are present in your git-tree but not
> > > > > > > in this series?
> > > > > > 
> > > > > > No, I must have been not clear enough on that. Our idea was to keep
> > > > > > I2C slave device nodes as an I2C controller's child nodes, according
> > > > > > to the current convention.
> > > > > > The 'sensor' nodes (the 'camera''s children) would only contain a
> > > > > > phandle to a respective I2C slave node.
> > > > > > 
> > > > > > This implies that we cannot access I2C bus in I2C client's device
> > > > > > probe() callback. An actual H/W access could begin only from within
> > > > > > and after invocation of v4l2_subdev .registered callback..
> > > > > 
> > > > > That's how I've envisioned the DT bindings for sensors as well, this
> > > > > sounds good. The real challenge will be to get hold of the subdev to
> > > > > register it without race conditions.
> > > > 
> > > > Hrm... That's how early pre-subdev versions of soc-camera used to work,
> > > > that's where all the <device>_video_probe() functions come from. But
> > > > then we switched to dynamic i2c device registration. Do we want to
> > > > switch all drivers back now?... Couldn't we "temporarily" use references
> > > > from subdevs to hosts until the clock API is available?
> > > 
> > > I don't think that requires a reference from subdevs to hosts in the DT.
> > > The subdev will need the host to be probed before a clock can be
> > > available so you won't be able to access the hardware in the probe()
> > > function in the generic case. You will need to wait until the
> > > registered() subdev operation is called, at which point the host can be
> > > accessed through the v4l2_device.
> > 
> > Sure, I understand, but that's exactly what we wanted to avoid -
> > succeeding client's i2c .probe() without even touching the hardware.
> 
> But should we allow host probe() to succeed if the sensor isn't present ?

I think we should, yes. The host hardware is there and functional - 
whether or not all or some of the clients are failing. Theoretically 
clients can also be hot-plugged. Whether and how many video device nodes 
we create, that's a different question.

Thanks
Guennadi
---
Guennadi Liakhovetski, Ph.D.
Freelance Open-Source Software Developer
http://www.open-technology.de/