Re: [RFC PATCH v2 12/16] media: i2c: add Maxim GMSL2/3 serializer and deserializer drivers

Jakub Kostiw
2025-05-07T07:28:19Z

> Can you revert the change you made to polarity_on_physical_lanes, and
> try the following?
>
> diff --git a/drivers/media/i2c/maxim-serdes/max9296a.c
> b/drivers/media/i2c/maxim-serdes/max9296a.c
> index f48f5b68a750..dea0518fd790 100644
> --- a/drivers/media/i2c/maxim-serdes/max9296a.c
> +++ b/drivers/media/i2c/maxim-serdes/max9296a.c
> @@ -474,7 +474,7 @@ static int max9296a_init_phy(struct max_des *des,
> struct max_des_phy *phy)
>                  */
>
>                 if (priv->info->polarity_on_physical_lanes)
> -                       map = phy->mipi.data_lanes[i];
> +                       map = phy->mipi.data_lanes[i] - 1;
>                 else
>                         map = i;
>
> data_lanes is 1-based (since 0 is the clock lane), but the bits
> in register 0x335 start from 0. That means we should adjust the
> values in data_lanes to be 0-based.

I have applied your patch and polarity settings seems to be correct now
(based on register contents).
However, I have came across another issue.
When I was debugging the driver for MAX96714, before I found out that
the issue was with polarity settings, I have commented out calls to
MAX9296A_DPLL_0. Probably because I thought it was there by mistake. I
totally forgot about that change.
Before applying your patch I reverted any changes to the driver, so
MAX9296A_DPLL_0 writes were back again. Sadly, video stream did not
work. So I began to wonder, and just for sake of testing, commented
these calls again (added some logs for quick tracing purposes):

diff --git a/drivers/media/i2c/maxim-serdes/max9296a.c
b/drivers/media/i2c/maxim-serdes/max9296a.c
index f48f5b68a..b24a8e2d6 100644
--- a/drivers/media/i2c/maxim-serdes/max9296a.c
+++ b/drivers/media/i2c/maxim-serdes/max9296a.c
@@ -391,6 +391,8 @@ static int max9296a_init_phy(struct max_des *des,
struct max_des_phy *phy)
* PHY1 Lane 1 = D3
*/

+       dev_info(priv->dev, "Using  %d lanes", num_data_lanes);
+
/* Configure a lane count. */
ret = regmap_update_bits(priv->regmap,
MAX9296A_MIPI_TX10(hw_index),
MAX9296A_MIPI_TX10_CSI2_LANE_CNT,
@@ -474,7 +476,7 @@ static int max9296a_init_phy(struct max_des *des,
struct max_des_phy *phy)
*/

if (priv->info->polarity_on_physical_lanes)
-                       map = phy->mipi.data_lanes[i];
+                       map = phy->mipi.data_lanes[i] - 1;
else
map = i;

@@ -484,6 +486,9 @@ static int max9296a_init_phy(struct max_des *des,
struct max_des_phy *phy)
if (phy->index == 0 && priv->info->phy0_lanes_0_1_on_second_phy)
val = ((val & 0x3) << 2) | ((val >> 2) & 0x3);

+       dev_info(priv->dev, "Val for MIPI_PHY5 (0_1): %lx",
FIELD_PREP(MAX9296A_MIPI_PHY5_PHY_POL_MAP_0_1, val));
+       dev_info(priv->dev, "Val for MIPI_PHY5 (2_3): %lx",
FIELD_PREP(MAX9296A_MIPI_PHY5_PHY_POL_MAP_2_3, val >> 2));
+
ret = regmap_update_bits(priv->regmap, MAX9296A_MIPI_PHY5(index),
MAX9296A_MIPI_PHY5_PHY_POL_MAP_0_1 |
MAX9296A_MIPI_PHY5_PHY_POL_MAP_2_3,
@@ -499,10 +504,10 @@ static int max9296a_init_phy(struct max_des *des,
struct max_des_phy *phy)
return ret;

/* Put DPLL block into reset. */
-       ret = regmap_clear_bits(priv->regmap, MAX9296A_DPLL_0(hw_index),
- MAX9296A_DPLL_0_CONFIG_SOFT_RST_N);
-       if (ret)
-               return ret;
+       //ret = regmap_clear_bits(priv->regmap, MAX9296A_DPLL_0(hw_index),
+       // MAX9296A_DPLL_0_CONFIG_SOFT_RST_N);
+       //if (ret)
+       //      return ret;

/* Set DPLL frequency. */
ret = regmap_update_bits(priv->regmap, MAX9296A_BACKTOP22(index),
@@ -519,10 +524,10 @@ static int max9296a_init_phy(struct max_des *des,
struct max_des_phy *phy)
return ret;

/* Pull DPLL block out of reset. */
-       ret = regmap_set_bits(priv->regmap, MAX9296A_DPLL_0(index),
-                             MAX9296A_DPLL_0_CONFIG_SOFT_RST_N);
-       if (ret)
-               return ret;
+       //ret = regmap_set_bits(priv->regmap, MAX9296A_DPLL_0(index),
+       //                    MAX9296A_DPLL_0_CONFIG_SOFT_RST_N);
+       //if (ret)
+       //      return ret;

if (dpll_freq > 1500000000ull) {
/* Enable initial deskew with 2 x 32k UI. */

To my surprise it works this way. I tested this 2 times back and forth.
Can these calls really cause some issues?