linux-kernel - Re: [PATCH 16/16] media: i2c: gmsl: Use 339Kbps I2C bit-rate

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Message-ID: <aa7d8a9c-93a0-8c14-4fe4-b831e7b45d88@ideasonboard.com>
Date:   Thu, 18 Feb 2021 16:07:30 +0000
From:   Kieran Bingham <kieran.bingham+renesas@...asonboard.com>
To:     Jacopo Mondi <jacopo+renesas@...ndi.org>,
        laurent.pinchart+renesas@...asonboard.com,
        niklas.soderlund+renesas@...natech.se, geert@...ux-m68k.org
Cc:     Mauro Carvalho Chehab <mchehab@...nel.org>,
        linux-media@...r.kernel.org, linux-renesas-soc@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 16/16] media: i2c: gmsl: Use 339Kbps I2C bit-rate

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....





> Signed-off-by: Jacopo Mondi <jacopo+renesas@...ndi.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;
>  
>