[PATCH v4 2/5] media: ov2640: add async probe function

Josh Wu josh.wu at atmel.com
Tue Dec 30 02:02:23 PST 2014

Hi, Laurent

On 12/30/2014 8:15 AM, Laurent Pinchart wrote:
> Hi Josh,
> On Monday 29 December 2014 16:28:02 Josh Wu wrote:
>> On 12/26/2014 6:06 PM, Laurent Pinchart wrote:
>>> On Friday 26 December 2014 10:14:26 Guennadi Liakhovetski wrote:
>>>> On Fri, 26 Dec 2014, Laurent Pinchart wrote:
>>>>> On Friday 26 December 2014 14:37:14 Josh Wu wrote:
>>>>>> On 12/25/2014 6:39 AM, Guennadi Liakhovetski wrote:
>>>>>>> On Mon, 22 Dec 2014, Josh Wu wrote:
>>>>>>>> On 12/20/2014 6:16 AM, Guennadi Liakhovetski wrote:
>>>>>>>>> On Fri, 19 Dec 2014, Josh Wu wrote:
>>>>>>>>>> On 12/19/2014 5:59 AM, Guennadi Liakhovetski wrote:
>>>>>>>>>>> On Thu, 18 Dec 2014, Josh Wu wrote:
>>>>>>>>>>>> To support async probe for ov2640, we need remove the code to get
>>>>>>>>>>>> 'mclk' in ov2640_probe() function. oterwise, if soc_camera host
>>>>>>>>>>>> is not probed in the moment, then we will fail to get 'mclk' and
>>>>>>>>>>>> quit the ov2640_probe() function.
>>>>>>>>>>>> So in this patch, we move such 'mclk' getting code to
>>>>>>>>>>>> ov2640_s_power() function. That make ov2640 survive, as we can
>>>>>>>>>>>> pass a NULL (priv-clk) to soc_camera_set_power() function.
>>>>>>>>>>>> And if soc_camera host is probed, the when ov2640_s_power() is
>>>>>>>>>>>> called, then we can get the 'mclk' and that make us
>>>>>>>>>>>> enable/disable soc_camera host's clock as well.
>>>>>>>>>>>> Signed-off-by: Josh Wu <josh.wu at atmel.com>
>>>>>>>>>>>> ---
>>>>>>>>>>>> v3 -> v4:
>>>>>>>>>>>> v2 -> v3:
>>>>>>>>>>>> v1 -> v2:
>>>>>>>>>>>>        no changes.
>>>>>>>>>>>> drivers/media/i2c/soc_camera/ov2640.c | 31  ++++++++++++++-------
>>>>>>>>>>>> 1 file changed, 21 insertions(+), 10 deletions(-)
>>>>>>>>>>>> diff --git a/drivers/media/i2c/soc_camera/ov2640.c
>>>>>>>>>>>> b/drivers/media/i2c/soc_camera/ov2640.c
>>>>>>>>>>>> index 1fdce2f..9ee910d 100644
>>>>>>>>>>>> --- a/drivers/media/i2c/soc_camera/ov2640.c
>>>>>>>>>>>> +++ b/drivers/media/i2c/soc_camera/ov2640.c
>>>>>>>>>>>> @@ -739,6 +739,15 @@ static int ov2640_s_power(struct v4l2_subdev
>>>>>>>>>>>> *sd, int on)
>>>>>>>>>>>>       	struct i2c_client *client = v4l2_get_subdevdata(sd);
>>>>>>>>>>>>       	struct soc_camera_subdev_desc *ssdd =
>>>>>>>>>>>> soc_camera_i2c_to_desc(client);
>>>>>>>>>>>>       	struct ov2640_priv *priv = to_ov2640(client);
>>>>>>>>>>>> +	struct v4l2_clk *clk;
>>>>>>>>>>>> +
>>>>>>>>>>>> +	if (!priv->clk) {
>>>>>>>>>>>> +		clk = v4l2_clk_get(&client->dev, "mclk");
>>>>>>>>>>>> +		if (IS_ERR(clk))
>>>>>>>>>>>> +			dev_warn(&client->dev, "Cannot get the mclk.
>>>>>>>>>>>> maybe soc-camera host is not probed yet.\n");
>>>>>>>>>>>> +		else
>>>>>>>>>>>> +			priv->clk = clk;
>>>>>>>>>>>> +	}
>>>>>>>>>>>>         	return soc_camera_set_power(&client->dev, ssdd, priv
>>>>>>>>>>>> ->clk, on);
>>>>>>>>>>>>       }
>>>>>>>> Just let me explained a little more details at first:
>>>>>>>> As my understanding, current the priv->clk is a v4l2_clk: mclk, which
>>>>>>>> is a wrapper clock in soc_camera.c. it can make soc_camera to call
>>>>>>>> camera host's clock_start() clock_stop(). As in ov2640, the real mck
>>>>>>>> (pck1) is in ov2640 dt node (xvclk). So the camera host's
>>>>>>>> clock_start()/stop() only need to enable/disable his peripheral
>>>>>>>> clock.
>>>>>>> I'm looking at the ov2640 datasheet. In the block diagram I only see
>>>>>>> one input clock - the xvclk. Yes, it can be supplied by the camera
>>>>>>> host controller, in which case it is natural for the camera host
>>>>>>> driver to own and control it, or it can be a separate clock device -
>>>>>>> either static or configurable. This is just a note to myself to
>>>>>>> clarify, that it's one and the same clock pin we're talking about.
>>>>>>> Now, from the hardware / DT PoV, I think, the DT should look like:
>>>>>>> a) in the ov2640 I2C DT node we should have a clock consumer entry,
>>>>>>> linking to a board-specific source.
>>>>>> That's what this patch series do right now.
>>>>>> In my patch 5/5 DT document said, ov2640 need a clock consumer which
>>>>>> refer to the xvclk input clock.
>>>>>> And it is a required property.
>>>>>>> b) if the ov2640 clock is supplied by a camera host, its DT entry
>>>>>>> should have a clock source subnode, to which ov2640 clock consumer
>>>>>>> entry should link. The respective camera host driver should then parse
>>>>>>> that clock subnode and register the respective clock with the V4L2
>>>>>>> framework, by calling v4l2_clk_register().
>>>>>> Ok, So in this case, I need to wait for the "mclk" in probe of ov2640
>>>>>> driver. So that I can be compatible for the camera host which provide
>>>>>> the clock source.
>>>>> Talking about mclk and xvclk is quite confusing. There's no mclk from an
>>>>> ov2640 point of view. The ov2640 driver should call
>>>>> v4l2_clk_get("xvclk").
>>>> Yes, I also was thinking about this, and yes, requesting a "xvclk" clock
>>>> would be more logical. But then, as you write below, if we let the
>>>> v4l2_clk wrapper first check for a CCF "xvclk" clock, say, none is found.
>>>> How do we then find the exported "mclk" V4L2 clock? Maybe v4l2_clk_get()
>>>> should use two names?..
>>> Given that v4l2_clk_get() is only used by soc-camera drivers and that they
>>> all call it with the clock name set to "mclk", I wonder whether we
>>> couldn't just get rid of struct v4l2_clk.id and ignore the id argument to
>>> v4l2_clk_get() when CCF isn't available. Maybe we've overdesigned
>>> v4l2_clk :-)
>> Sorry, I'm not clear about how to implement what you discussed here.
>> Do you mean, In the ov2640 driver:
>> 1. need to remove the patch 4/5, "add a master clock for sensor"
> No, the sensor has a clock input named "xvclk", the ov2640 driver should thus
> manage that clock. Patch 4/5 does the right thing.
> However, I've just realized that it will cause regressions on the i.MX27,
> i.MX31 and i.MX37 3DS development boards that use the sensor without
> registering a clock named xvclk. You should fix that as part of the patch
> series.

Thanks for the information.
So I think to be compatible with i.MX series board, I have two ways:
  1. Make the xvclk clock be optional in ov2640 driver. After the i.MX 
series board switch to CCF, and we can change it to mandatory.
  2. switch the i.MX host driver to DT, and add the xvclk to their dts.

As I am not similar with i.MX board and cannot test for them. I prefer 
to the #1, which is simple and work well. We can change the property 
when CCF & DT is introduced to i.MX boards.

Best Regards,
Josh Wu

>> 2. need to register a "xvclk" v4l2 clock which is a CCF clock. Or this
>> part can put in soc_camera.c
>> 3. So in ov2640_probe(), need to call v4l2_clk_get("xvclk"), which will do
>>        a. Get CCF clock "xvclk" by call devm_clk_get("xvclk"), and if
>> failed then return the error code.
>>        b. Get the v4l2 clock "mclk", if failed then return the error code.
> v4l2_clk_get() was introduced as a temporary workaround for platforms that
> don't support CCF yet. It might be possible to use clk_get() directly here as
> the i.MX platforms support CCF (as far as I'm concerned you don't need to care
> about out-of-tree non-DT platforms). Otherwise we'll need to stick to
> v4l2_clk_get(), in which case the v4l2_clk_get() implementation will need to
> be modified to call clk_get() first and fall back to the V4L2 private clock
> list.
>> 4. In ov2640_s_power(), we'll call soc_camera_set_power(..., priv->clk,
>> ...) to enable "xvclk" and "mclk" clock.
> And looking at the implementation of soc_camera_power_on() and
> soc_camera_power_off(), I realize that soc-camera expects to manage a v4l2_clk
> itself...
> Guennadi, could you please detail the steps that Josh should follow, keeping
> in mind that the goal is to get rid of v4l2_clk_get() in the not too distant
> future ? The fact that soc-camera host drivers start their own hardware in
> their .clock_start() operation, called through the mclk pseudo-clock, makes
> all this pretty messy.
> Do you think you'll have time to properly migrate soc-camera to DT in the not
> too distant future ?
>> Please correct me if I misunderstand your meaning?
>> Best Regards,
>> Josh Wu
>>>>>>> c) if the ov2640 clock is supplied by a different clock source, the
>>>>>>> respective driver should parse it and also eventually call
>>>>>>> v4l2_clk_register().
>>>>>>> Implementing case (b) above is so far up to each individual
>>>>>>> (soc-camera) camera host driver. In soc-camera host drivers don't
>>>>>>> register V4L2 clocks themselves, as you correctly noticed, they just
>>>>>>> provide a .clock_start() and a .clock_stop() callbacks. The
>>>>>>> registration is done by the soc-camera core.
>>>>>>> If I understand correctly you have case (c). Unfortunately, this case
>>>>>>> isn't supported atm. I think, a suitable way to do this would be:
>>>>>>> (1) modify soc-camera to not register a V4L2 clock if the host doesn't
>>>>>>> provide the required callbacks.
>>>>>>> (2) hosts should recognise configurations, in which they don't supply
>>>>>>> the master clock to clients and not provide the callbacks then.
>>>>>>> (3) a separate driver should register a suitable V4L2 clock.
>>>>>>> Whereas I don't think we need to modify camera drivers. Their
>>>>>>> requesting of a V4L2 clock is correct as is.
>>>>>>> Some more fine-print: if the clock is supplied by a generic device, it
>>>>>>> would be wrong for it to register a V4L2 clock. It should register a
>>>>>>> normal CCF clock, and a separate V4L2 driver should create a V4L2
>>>>>>> clock from it. This isn't implemented either and we've been talking
>>>>>>> about it for a while now...
>>>>> v4l2_clk_get() should try to get the clock from CCF with a call to
>>>>> clk_get() first, and then look at the list of v4l2-specific clocks.
>>>> Yes, how will it find the "mclk" when "xvclk" (or any other name) is
>>>> requested? We did discuss this in the beginning and agreed to use a fixed
>>>> clock name for the time being...
>>> Please see above.
>>>>> That's at least how I had envisioned it when v4l2_clk_get() was
>>>>> introduced. Let's remember that v4l2_clk was designed as a temporary
>>>>> workaround for platforms not implementing CCF yet. Is that still needed,
>>>>> or could be instead just get rid of it now ?
>>>> I didn't check, but I don't think all platforms, handled by soc-camera,
>>>> support CCF yet.
>>> After a quick check it looks like only OMAP1 and SH Mobile are missing.
>>> Atmel, MX2, MX3 and R-Car all support CCF. PXA27x has CCF support but
>>> doesn't enable it yet for an unknown (to me) reason.
>>> The CEU driver is used on both arch/sh and arch/arm/mach-shmobile. The
>>> former will most likely never receive CCF support, and the latter is
>>> getting fixed. As arch/sh isn't maintained anymore I would be fine with
>>> dropping CEU support for it.
>>> OMAP1 is thus the only long-term show-stopper. What should we do with it ?

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