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SubjectRe: [PATCH 16/16] media: i2c: gmsl: Use 339Kbps I2C bit-rate
Hi Jacopo,

Thank you for the patch.

On Thu, Feb 18, 2021 at 04:07:30PM +0000, Kieran Bingham wrote:
> On 16/02/2021 17:41, Jacopo Mondi wrote:
> > With the camera modules initialization routines now running with
> > the noise immunity threshold enabled, it is possible to restore
> > the bit rate of the I2C transactions transported on the GMSL control
> > channel to 339 Kbps.
> >
> > The 339 Kbps bit rate represents the default setting for the serializer
> > and the deserializer chips, and the setup/hold time and slave timeout
> > time in use are calibrate to support that rate.
>
> s/calibrate/calibrated/
>
> Does that mean the setup/hold time and timeouts should be adjusted based
> on the i2c speed? (which we have not been doing?)
>
> With all of your other reliability improvements, does *this* change
> alone have any difference or impact on reliability?
>
> I.e. if we go slower (stay at current speed) - would we be more reliable?
>
> Is there a reliability improvement by making this speed faster?
>
> I presume we don't have a way to convey the i2c bus speed between the
> max9286 and the max9271 currently? Seems a bit like a bus parameter....

There's a max bus speed DT parameter that we can use. And I think we
should, as, in theory at least, there's no guarantee that all the
devices behind the serializer can operate at 400kbps.

> > Signed-off-by: Jacopo Mondi <jacopo+renesas@jmondi.org>
> > ---
> > drivers/media/i2c/max9286.c | 2 +-
> > drivers/media/i2c/rdacm20.c | 2 +-
> > drivers/media/i2c/rdacm21.c | 2 +-
> > 3 files changed, 3 insertions(+), 3 deletions(-)
> >
> > diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> > index aa01d5bb79ef..0b620f2f8c41 100644
> > --- a/drivers/media/i2c/max9286.c
> > +++ b/drivers/media/i2c/max9286.c
> > @@ -330,7 +330,7 @@ static int max9286_i2c_mux_init(struct max9286_priv *priv)
> > static void max9286_configure_i2c(struct max9286_priv *priv, bool localack)
> > {
> > u8 config = MAX9286_I2CSLVSH_469NS_234NS | MAX9286_I2CSLVTO_1024US |
> > - MAX9286_I2CMSTBT_105KBPS;
> > + MAX9286_I2CMSTBT_339KBPS;
> >
> > if (localack)
> > config |= MAX9286_I2CLOCACK;
> > diff --git a/drivers/media/i2c/rdacm20.c b/drivers/media/i2c/rdacm20.c
> > index 0632ef98eea7..d45e8b0e52a0 100644
> > --- a/drivers/media/i2c/rdacm20.c
> > +++ b/drivers/media/i2c/rdacm20.c
> > @@ -450,7 +450,7 @@ static int rdacm20_init(struct v4l2_subdev *sd, unsigned int val)
> > ret = max9271_configure_i2c(&dev->serializer,
> > MAX9271_I2CSLVSH_469NS_234NS |
> > MAX9271_I2CSLVTO_1024US |
> > - MAX9271_I2CMSTBT_105KBPS);
> > + MAX9271_I2CMSTBT_339KBPS);
> > if (ret)
> > return ret;
> >
> > diff --git a/drivers/media/i2c/rdacm21.c b/drivers/media/i2c/rdacm21.c
> > index 80b6f16f87a8..552985026458 100644
> > --- a/drivers/media/i2c/rdacm21.c
> > +++ b/drivers/media/i2c/rdacm21.c
> > @@ -442,7 +442,7 @@ static int rdacm21_init(struct v4l2_subdev *sd, unsigned int val)
> > ret = max9271_configure_i2c(&dev->serializer,
> > MAX9271_I2CSLVSH_469NS_234NS |
> > MAX9271_I2CSLVTO_1024US |
> > - MAX9271_I2CMSTBT_105KBPS);
> > + MAX9271_I2CMSTBT_339KBPS);
> > if (ret)
> > return ret;
> >

--
Regards,

Laurent Pinchart

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