Message-ID: <20161103230501.GJ3217@valkosipuli.retiisi.org.uk>
Date:   Fri, 4 Nov 2016 01:05:01 +0200
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Sebastian Reichel <sre@...nel.org>
Cc:     Pavel Machek <pavel@....cz>, ivo.g.dimitrov.75@...il.com,
        pali.rohar@...il.com, linux-media@...r.kernel.org,
        galak@...eaurora.org, mchehab@....samsung.com,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v4] media: Driver for Toshiba et8ek8 5MP sensor

Hi Sebastian,

On Thu, Nov 03, 2016 at 11:48:43PM +0100, Sebastian Reichel wrote:
> Hi,
> 
> On Tue, Nov 01, 2016 at 12:54:08AM +0200, Sakari Ailus wrote:
> > > > Thanks, this answered half of my questions already. ;-)
> > > :-).
> > > 
> > > I'll have to go through the patches, et8ek8 driver is probably not
> > > enough to get useful video. platform/video-bus-switch.c is needed for
> > > camera switching, then some omap3isp patches to bind flash and
> > > autofocus into the subdevice.
> > > 
> > > Then, device tree support on n900 can be added.
> > 
> > I briefly discussed with with Sebastian.
> > 
> > Do you think the elusive support for the secondary camera is worth keeping
> > out the main camera from the DT in mainline? As long as there's a reasonable
> > way to get it working, I'd just merge that. If someone ever gets the
> > secondary camera working properly and nicely with the video bus switch,
> > that's cool, we'll somehow deal with the problem then. But frankly I don't
> > think it's very useful even if we get there: the quality is really bad.
> 
> If we want to keep open the option to add proper support for the
> second camera, we could also add the bus switch and not add the
> front camera node in DT. Then adding the front camera does not
> require DT or userspace API changes. It would need an additional
> DT quirk in arch/arm/mach-omap2/board-generic.c for RX51, which
> adds the CCP2 bus settings from the camera node to the bus
> switch node to keep isp_of_parse_node happy. That should be
> easy to implement and not add much delay in upstreaming.

By adding the video bus switch we have a little bit more complex system as a
whole. The V4L2 async does not currently support this. There's more here:

<URL:http://www.spinics.net/lists/linux-media/msg107262.html>

What I thought was that once we have everything that's required in place, we
can just change what's in DT. But the software needs to continue to work
with the old DT content.

> For actually getting both cameras available with runtime-switching
> the proper solution would probably involve moving the parsing of
> the bus-settings to the sensor driver and providing a callback.
> This callback can be called by omap3isp when it wants to configure
> the phy (which is basically when it starts streaming). That seems
> to be the only place needing the buscfg anyways.
> 
> Then the video-bus-switch could do something like this (pseudocode):
> 
> static void get_buscfg(struct *this, struct *buscfg) {
>     if (selected_cam == 0)
>         return this->sensor_a->get_buscfg(buscfg);
>     else
>         return this->sensor_b->get_buscfg(buscfg);
> }
> 
> Regarding the usefulness: I noticed, that the Neo900 people also
> plan to have the bus-switch [0]. It's still the same crappy front-cam,
> though. Nevertheless it might be useful for testing. It has nice
> test-image capabilities, which might be useful for regression
> testing once everything is in place.
> 
> [0] http://neo900.org/stuff/block-diagrams/neo900/neo900.html

Seriously? I suppose there should be no need for that anymore, is there?

I think they wanted to save one GPIO in order to shave off 0,0001 cents from
the manufacturing costs or something like that. And the result is...
painful. :-I

-- 
Kind regards,

Sakari Ailus
e-mail: sakari.ailus@....fi	XMPP: sailus@...iisi.org.uk

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