Hi Jacopo,
On 15/10/2020 19:27, Jacopo Mondi wrote:
> Instrument the function that configures the reverse channel with a
> programmable amplitude value.
>
> This change serves to prepare to adjust the reverse channel amplitude
> depending on the remote end high-threshold configuration.
>
> Signed-off-by: Jacopo Mondi <jacopo+rene...@jmondi.org>
> ---
> drivers/media/i2c/max9286.c | 22 ++++++++++++++++------
> 1 file changed, 16 insertions(+), 6 deletions(-)
>
> diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> index 89a7248f5c25..163e102199e3 100644
> --- a/drivers/media/i2c/max9286.c
> +++ b/drivers/media/i2c/max9286.c
> @@ -906,19 +906,29 @@ static void max9286_v4l2_unregister(struct max9286_priv
> *priv)
> * Probe/Remove
> */
>
> -static void max9286_reverse_channel_setup(struct max9286_priv *priv)
> +static void max9286_reverse_channel_setup(struct max9286_priv *priv,
> + unsigned int chan_amplitude)
> {
> + /* Reverse channel transmission time: default to 1. */
> + u8 chan_config = MAX9286_REV_TRF(1);
> +
> /*
> * Reverse channel setup.
> *
> * - Enable custom reverse channel configuration (through register 0x3f)
> * and set the first pulse length to 35 clock cycles.
> - * - Increase the reverse channel amplitude to 170mV to accommodate the
> - * high threshold enabled by the serializer driver.
> + * - Adjust reverse channel amplitude: values > 130 are programmed
> + * using the additional +100mV REV_AMP_X boost flag
> */
> max9286_write(priv, 0x3f, MAX9286_EN_REV_CFG | MAX9286_REV_FLEN(35));
> - max9286_write(priv, 0x3b, MAX9286_REV_TRF(1) | MAX9286_REV_AMP(70) |
> - MAX9286_REV_AMP_X);
> +
Should we also clamp to min/max values at all?
Probably not needed, as it's only an internal helper.
> + if (chan_amplitude > 100) {
> + /* It is not possible express values (100 < x < 130) */
'possible to express'
> + chan_amplitude = chan_amplitude < 130
> + ? 30 : chan_amplitude - 100;
We could round < 115 to 100, and >= 115 to 130, but that's probably more
effort that it's worth, so I think this is fine.
I think it's really helpful to codify this parameter though:
Reviewed-by: Kieran Bingham <kieran.bingham+rene...@ideasonboard.com>
> + chan_config |= MAX9286_REV_AMP_X;
> + }
> + max9286_write(priv, 0x3b, chan_config |
> MAX9286_REV_AMP(chan_amplitude));
> usleep_range(2000, 2500);
> }
>
> @@ -957,7 +967,7 @@ static int max9286_setup(struct max9286_priv *priv)
> * only. This should be disabled after the mux is initialised.
> */
> max9286_configure_i2c(priv, true);
> - max9286_reverse_channel_setup(priv);
> + max9286_reverse_channel_setup(priv, 170);
>
> /*
> * Enable GMSL links, mask unused ones and autodetect link
>
