linux-kernel - Re: [PATCH v7 16/34] [media] add Omnivision OV5640 sensor driver

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Message-ID: <20170601082659.GJ1019@valkosipuli.retiisi.org.uk>
Date:   Thu, 1 Jun 2017 11:26:59 +0300
From:   Sakari Ailus <sakari.ailus@....fi>
To:     Pavel Machek <pavel@....cz>
Cc:     Steve Longerbeam <slongerbeam@...il.com>, robh+dt@...nel.org,
        mark.rutland@....com, shawnguo@...nel.org, kernel@...gutronix.de,
        fabio.estevam@....com, linux@...linux.org.uk, mchehab@...nel.org,
        hverkuil@...all.nl, nick@...anahar.org, markus.heiser@...marIT.de,
        p.zabel@...gutronix.de, laurent.pinchart+renesas@...asonboard.com,
        bparrot@...com, geert@...ux-m68k.org, arnd@...db.de,
        sudipm.mukherjee@...il.com, minghsiu.tsai@...iatek.com,
        tiffany.lin@...iatek.com, jean-christophe.trotin@...com,
        horms+renesas@...ge.net.au, niklas.soderlund+renesas@...natech.se,
        robert.jarzmik@...e.fr, songjun.wu@...rochip.com,
        andrew-ct.chen@...iatek.com, gregkh@...uxfoundation.org,
        shuah@...nel.org, sakari.ailus@...ux.intel.com,
        devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org, linux-media@...r.kernel.org,
        devel@...verdev.osuosl.org,
        Steve Longerbeam <steve_longerbeam@...tor.com>
Subject: Re: [PATCH v7 16/34] [media] add Omnivision OV5640 sensor driver

Hi Pavel,

On Wed, May 31, 2017 at 09:58:21PM +0200, Pavel Machek wrote:
> Hi!
> 
> > +/* min/typical/max system clock (xclk) frequencies */
> > +#define OV5640_XCLK_MIN  6000000
> > +#define OV5640_XCLK_MAX 24000000
> > +
> > +/*
> > + * FIXME: there is no subdev API to set the MIPI CSI-2
> > + * virtual channel yet, so this is hardcoded for now.
> > + */
> > +#define OV5640_MIPI_VC	1
> 
> Can the FIXME be fixed?

Yes, but it's quite a bit of work. It makes sense to use a static virtual
channel for now. A patchset which is however incomplete can be found here:

<URL:https://git.linuxtv.org/sailus/media_tree.git/log/?h=vc>

For what it's worth, all other devices use virtual channel zero for image
data and so should this one.

> 
> > +/*
> > + * image size under 1280 * 960 are SUBSAMPLING
> 
> -> Image
> 
> > + * image size upper 1280 * 960 are SCALING
> 
> above?
> 
> > +/*
> > + * FIXME: all of these register tables are likely filled with
> > + * entries that set the register to their power-on default values,
> > + * and which are otherwise not touched by this driver. Those entries
> > + * should be identified and removed to speed register load time
> > + * over i2c.
> > + */
> 
> load->loading? Can the FIXME be fixed?
> 
> > +	/* Auto/manual exposure */
> > +	ctrls->auto_exp = v4l2_ctrl_new_std_menu(hdl, ops,
> > +						 V4L2_CID_EXPOSURE_AUTO,
> > +						 V4L2_EXPOSURE_MANUAL, 0,
> > +						 V4L2_EXPOSURE_AUTO);
> > +	ctrls->exposure = v4l2_ctrl_new_std(hdl, ops,
> > +					    V4L2_CID_EXPOSURE_ABSOLUTE,
> > +					    0, 65535, 1, 0);
> 
> Is exposure_absolute supposed to be in microseconds...?

Yes. OTOH V4L2_CID_EXPOSURE has no defined unit, so it's a better fit IMO.
Way more drivers appear to be using EXPOSURE than EXPOSURE_ABSOLUTE, too.

Ideally we should have only one control for exposure.

-- 
Regards,

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