linux-kernel - Re: [PATCH v4 04/21] doc: media/v4l-drivers: Add Qualcomm Camera Subsystem driver document

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Message-ID: <97228890-39c1-6c85-ed74-0e1e62b83868@zonque.org>
Date:   Tue, 29 Aug 2017 19:02:42 +0200
From:   Daniel Mack <daniel@...que.org>
To:     Todor Tomov <todor.tomov@...aro.org>
Cc:     mchehab@...nel.org, hans.verkuil@...co.com, s.nawrocki@...sung.com,
        sakari.ailus@....fi, linux-media@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-arm-msm@...r.kernel.org
Subject: Re: [PATCH v4 04/21] doc: media/v4l-drivers: Add Qualcomm Camera
 Subsystem driver document

Hi Todor,

On 08/28/2017 09:10 AM, Todor Tomov wrote:
> On 25.08.2017 17:10, Daniel Mack wrote:
>> I have a userspace test setup that works fine for USB webcams, but when
>> operating on any of the video devices exposed by this driver, the
>> lowlevel functions such as .s_power of the ISPIF, CSID, CSIPHY and the
>> sensor driver layers aren't called into.
> 
> Have you activated the media controller links? The s_power is called
> when the subdev is part of a pipeline in which the video device node
> is opened. You can see example configurations for the Qualcomm CAMSS
> driver on:
> https://github.com/96boards/documentation/blob/master/ConsumerEdition/DragonBoard-410c/Guides/CameraModule.md
> This will probably answer most of your questions.

Yes, it does, thank you! I didn't expect the necessity for any manual
setup on this level due to this sentence in the documentation:

> Runtime configuration of the hardware (updating settings while
> streaming) is not required to implement the currently supported
> functionality.

I hence assumed there is a fixed mapping that is partly derived from DTS
information etc. Anyway, this seems to work now, so thanks a bunch for
the pointer!

Another thing that confused me for a while is the CCI driver, which also
exposes media pads. I have the cameras connected to a regular I2C bus
however, and it seems to work fine. That just leaves the question why
this CCI driver exists at all.

I also have some more questions, but they are even more platform
specific, so I'll rather post them in the 96boards forum.

Thanks again!
Daniel