Hi Kieran,
On Wed, Mar 18, 2020 at 09:57:48AM +0000, Kieran Bingham wrote:
> Hi Jacopo,
>
> On 16/03/2020 20:27, Jacopo Mondi wrote:
> > Parse the 'maxim,reverse-channel-amplitude' property value and cache its
> > content to later program the initial reverse channel amplitude.
> >
> > Only support 100mV and 170mV values for the moment. The property could
> > be easily expanded to support more values.
>
> Can we (in the future) support arbitrary values from a range, or only
> from a fixed list?
Good question. The 0x3b register of the deserializer is not documented
in my datasheet version, I got this from the application developer
guide that reports
Increase reverse amplitude from 100mV to
170mV. This compensates for the higher
threshold of step 5.
and reports the following list of supported values in the 0x3b
register description.
Reverse channel amplitude
000 = 30mV
001 = 40mV
010 = 50mV
011 = 60mV
100 = 70mV
101 = 80mV
110 = 90mV
111 = 100mV
with an optional +100mV boost option.
Going forward we can add more values to the list of supported ones in
the bindings and control their configuration in the driver.
Maybe worth noting it down with a fixme note ?
>
> > Signed-off-by: Jacopo Mondi <jacopo+renesas@xxxxxxxxxx>
> > ---
> > drivers/media/i2c/max9286.c | 39 ++++++++++++++++++++++++++++++++-----
> > 1 file changed, 34 insertions(+), 5 deletions(-)
> >
> > diff --git a/drivers/media/i2c/max9286.c b/drivers/media/i2c/max9286.c
> > index 0357515860b2..24af8002535e 100644
> > --- a/drivers/media/i2c/max9286.c
> > +++ b/drivers/media/i2c/max9286.c
> > @@ -168,6 +168,7 @@ struct max9286_priv {
> > struct max9286_source sources[MAX9286_NUM_GMSL];
> > struct v4l2_async_notifier notifier;
> >
> > + u32 reverse_chan_amp;
> > u32 overlap_window;
> > };
> >
> > @@ -479,10 +480,15 @@ static int max9286_notify_bound(struct v4l2_async_notifier *notifier,
> > * All enabled sources have probed and enabled their reverse control
> > * channels:
> > *
> > - * - Verify all configuration links are properly detected
> > + * - Increase reverse channel amplitude to 170mV if not initially
> > + * compensated
> > * - Disable auto-ack as communication on the control channel are now
> > * stable.
> > */
> > + if (priv->reverse_chan_amp == 100)
> > + max9286_write(priv, 0x3b, MAX9286_REV_TRF(1) |
> > + MAX9286_REV_AMP(70) | MAX9286_REV_AMP_X);
> > +
> > max9286_check_config_link(priv, priv->source_mask);
> >
> > /*
> > @@ -830,6 +836,8 @@ static void max9286_v4l2_unregister(struct max9286_priv *priv)
> >
> > static int max9286_setup(struct max9286_priv *priv)
> > {
> > + u8 chan_amp = MAX9286_REV_TRF(1);
> > +
> > /*
> > * Link ordering values for all enabled links combinations. Orders must
> > * be assigned sequentially from 0 to the number of enabled links
> > @@ -869,12 +877,18 @@ static int max9286_setup(struct max9286_priv *priv)
> > *
> > * - 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.
> > + * - Set initial reverse channel amplitude according the DTS property.
> > + * If the initial channel amplitude is 100mV it should be increase
> > + * later after the serializers high threshold have been enabled.
> > + * If the initial value is 170mV the serializer has been
> > + * pre-programmed and we can compensate immediately.> */
> > 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);
> > + if (priv->reverse_chan_amp == 100)
> > + chan_amp |= MAX9286_REV_AMP(100);
> > + else
> > + chan_amp |= MAX9286_REV_AMP(70) | MAX9286_REV_AMP_X;
> > + max9286_write(priv, 0x3b, chan_amp);
> > usleep_range(2000, 2500);
> >
> > /*
> > @@ -1069,6 +1083,21 @@ static int max9286_parse_dt(struct max9286_priv *priv)
> > return -EINVAL;
> > }
> >
> > + ret = of_property_read_u32(dev->of_node, "maxim,reverse-channel-amplitude",
> > + &priv->reverse_chan_amp);
> > + if (ret) {
> > + dev_err(dev,
> > + "Missing property \"maxim,reverse-channel-amplitude\"\n");
> > + of_node_put(dev->of_node);
> > + return -EINVAL;
> > + }
> > + if (priv->reverse_chan_amp != 100 && priv->reverse_chan_amp != 170) {
> > + dev_err(dev, "Unsupported channel amplitude %umV\n",
> > + priv->reverse_chan_amp);
> > + of_node_put(dev->of_node);
> > + return -EINVAL;
> > + }
> > +
> > i2c_mux = of_find_node_by_name(dev->of_node, "i2c-mux");
> > if (!i2c_mux) {
> > dev_err(dev, "Failed to find i2c-mux node\n");
> >
>
