linux-kernel - Re: [PATCH] media: i2c: OV5647: gate clock lane before stream on

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Date:   Mon, 07 Aug 2017 10:17:31 +0200
From:   Philipp Zabel <p.zabel@...gutronix.de>
To:     Jacob Chen <jacobchen110@...il.com>
Cc:     "open list:ARM/Rockchip SoC..." <linux-rockchip@...ts.infradead.org>,
        linux-kernel@...r.kernel.org, roliveir@...opsys.com,
        Linux Media Mailing List <linux-media@...r.kernel.org>,
        Mauro Carvalho Chehab <mchehab@...nel.org>,
        vladimir_zapolskiy@...tor.com,
        Hans Verkuil <hans.verkuil@...co.com>,
        sakari.ailus@...ux.intel.com, Jacob Chen <jacob-chen@...wrt.com>,
        slongerbeam@...il.com, robh+dt@...nel.org, lolivei@...opsys.com
Subject: Re: [PATCH] media: i2c: OV5647: gate clock lane before stream on

Hi Jacob,

On Mon, 2017-08-07 at 15:11 +0800, Jacob Chen wrote:
> Hi all,
> 
> 2017-07-25 10:34 GMT+08:00 Jacob Chen <jacob-chen@...wrt.com>:
> > According to datasheet, BIT5 in reg-0x4800 are used to
> > enable/disable clock lane gate.
> >
> > It's wrong to make clock lane free running before
> > sensor stream on was called, while the mipi phy
> > are not initialized.
> >
> > Signed-off-by: Jacob Chen <jacob-chen@...wrt.com>
>>
> > ---
> >  drivers/media/i2c/ov5647.c | 10 +++++++++-
> >  1 file changed, 9 insertions(+), 1 deletion(-)
> >
> > diff --git a/drivers/media/i2c/ov5647.c b/drivers/media/i2c/ov5647.c
> > index 95ce90f..d3e6fd0 100644
> > --- a/drivers/media/i2c/ov5647.c
> > +++ b/drivers/media/i2c/ov5647.c
> > @@ -253,6 +253,10 @@ static int ov5647_stream_on(struct v4l2_subdev *sd)
> >  {
> >         int ret;
> >
> > +       ret = ov5647_write(sd, 0x4800, 0x04);
> > +       if (ret < 0)
> > +               return ret;
> > +
> >         ret = ov5647_write(sd, 0x4202, 0x00);
> >         if (ret < 0)
> >                 return ret;
> > @@ -264,6 +268,10 @@ static int ov5647_stream_off(struct v4l2_subdev *sd)
> >  {
> >         int ret;
> >
> > +       ret = ov5647_write(sd, 0x4800, 0x25);
> > +       if (ret < 0)
> > +               return ret;
> > +
> >         ret = ov5647_write(sd, 0x4202, 0x0f);
> >         if (ret < 0)
> >                 return ret;
> > @@ -320,7 +328,7 @@ static int __sensor_init(struct v4l2_subdev *sd)
> >                         return ret;
> >         }
> >
> > -       return ov5647_write(sd, 0x4800, 0x04);
> > +       return ov5647_stream_off(sd);
> >  }
> >
> >  static int ov5647_sensor_power(struct v4l2_subdev *sd, int on)
> > --
> > 2.7.4
> >
> 
> Can anyone comment on it?
> 
> I saw there is a same discussion in  https://patchwork.kernel.org/patch/9569031/
> There is a comment in i.MX CSI2 driver.
> "
> Configure MIPI Camera Sensor to put all Tx lanes in LP-11 state.
> This must be carried out by the MIPI sensor's s_power(ON) subdev
> op.
> "
> That's what this patch do, sensor driver should make sure that clock
> lanes are in stop state while not streaming.

This is not the same, as far as I can tell. BIT(5) is just clock lane
gating, as you describe above. To put the bus into LP-11 state, BIT(2)
needs to be set.

regards
Philipp