linux-kernel - Re: [PATCH v2 2/2] media: i2c: Add imx283 camera sensor driver

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Date: Mon, 11 Mar 2024 16:42:46 +0000
From: Kieran Bingham <kieran.bingham@...asonboard.com>
To: Sakari Ailus <sakari.ailus@...ux.intel.com>
Cc: Umang Jain <umang.jain@...asonboard.com>, linux-media@...r.kernel.org, Laurent Pinchart <laurent.pinchart@...asonboard.com>, willl will <will@...lwhang.com>, Mauro Carvalho Chehab <mchehab@...nel.org>, Hans Verkuil <hverkuil-cisco@...all.nl>, Hans de Goede <hdegoede@...hat.com>, Tomi Valkeinen <tomi.valkeinen@...asonboard.com>, Alain Volmat <alain.volmat@...s.st.com>, Paul Elder <paul.elder@...asonboard.com>, Mehdi Djait <mehdi.djait@...tlin.com>, Bingbu Cao <bingbu.cao@...el.com>, Andy Shevchenko <andy.shevchenko@...il.com>, Sebastian Reichel <sre@...nel.org>, Jacopo Mondi <jacopo.mondi@...asonboard.com>, open list <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 2/2] media: i2c: Add imx283 camera sensor driver

Quoting Sakari Ailus (2024-03-11 16:29:23)
> Hi Kieran,
> 
> On Mon, Mar 11, 2024 at 12:28:19PM +0000, Kieran Bingham wrote:
> > Hi Sakari, Umang,
> > 
> > I've replied inline below to a couple of points that I was responsible for.
> > 
> > > 
> > > > +
> > > > +struct imx283 {
> > > > +     struct device *dev;
> > > > +     struct regmap *cci;
> > > > +
> > > > +     const struct imx283_input_frequency *freq;
> > > > +
> > > > +     struct v4l2_subdev sd;
> > > > +     struct media_pad pad;
> > > > +
> > > > +     struct clk *xclk;
> > > > +
> > > > +     struct gpio_desc *reset_gpio;
> > > > +     struct regulator_bulk_data supplies[ARRAY_SIZE(imx283_supply_name)];
> > > > +
> > > > +     /* V4L2 Controls */
> > > > +     struct v4l2_ctrl_handler ctrl_handler;
> > > > +     struct v4l2_ctrl *exposure;
> > > > +     struct v4l2_ctrl *vblank;
> > > > +     struct v4l2_ctrl *hblank;
> > > > +     struct v4l2_ctrl *vflip;
> > > > +
> > > > +     unsigned long link_freq_bitmap;
> > > > +
> > > > +     u16 hmax;
> > > > +     u32 vmax;
> > > > +};
> > > > +
> > > > +static inline struct imx283 *to_imx283(struct v4l2_subdev *_sd)
> > > > +{
> > > > +     return container_of(_sd, struct imx283, sd);
> > > 
> > > It's a function, you can call _sd sd instead.
> > 
> > Except then that could 'look' like it is passed as the first and third
> > argument to container_of...
> 
> It's really a non-issue: the third argument is a field name, not a
> variable.

That's not so easy to determine when the args are the same name.., but
it's fine with me either way.

> > But if it's fine / accepted otherwise then sure.
> 
> And please use container_of_const(). :)

Ack. Or rather ... I'll leave that to Umang to handle, as he's managing
this driver now.

> > > > +
> > > > +/* Determine the exposure based on current hmax, vmax and a given SHR */
> > > > +static u64 imx283_exposure(struct imx283 *imx283,
> > > > +                        const struct imx283_mode *mode, u64 shr)
> > > > +{
> > > > +     u32 svr = 0; /* SVR feature is not currently supported */
> > > 
> > > What does this refer to? I guess you could just drop it as well if it's not
> > > supported?
> > 
> > Keeping this will keep the calculation matching the datasheet, and
> > provide clear value for what to update when we/others return to enable
> > long exposures.
> > 
> > So it would be nice to keep as it sort of documents/tracks the
> > datasheet.
> 
> Ack.
> 
> > 
> > 
> > > > +     u32 hmax = imx283->hmax;
> > > > +     u64 vmax = imx283->vmax;
> > > 
> > > You're not changing the values here. I wouldn't introduce temporary
> > > variables just for that.
> > > 
> > > > +     u32 offset;
> > > > +     u64 numerator;
> > > > +
> > > > +     /* Number of clocks per internal offset period */
> > > > +     offset = mode->mode == IMX283_MODE_0 ? 209 : 157;
> > > 
> > > Shouldn't this be in the mode definition?
> > 
> > It could be, but then there would be one copy of 209, and 9 copies of
> > 157. 
> 
> That would still be specified explicitly. Someone adding a new mode would
> easily miss this.
> 
> Or, if you can, derive this from something else that is now a part of the
> mode itself.

I don't understand the above, other than ... That's exactly what we're
doing here.

*Only* MODE_0 has an offset of 209 in the datasheet. All other modes are
157.

This is the table being codified:
  https://pasteboard.co/OsKf4VX7rtrS.png

--
Kieran