[PATCH v1 4/8] MT9M114: Add option to bypass PLL

Mathis Foerst
2025-02-26T15:40:07Z

The MT9M114 sensor has an internal PLL that generates the required SYSCLK
from EXTCLK. It also has the option to bypass the PLL and use EXTCLK
directly as SYSCLK.
The current driver implementation uses a hardcoded PLL configuration that
requires a specific EXTCLK frequency. Depending on the available clocks,
it can be desirable to use a different PLL configuration or to bypass it.

Read the property 'bypass-pll' from the DT in mt9m114_parse_dt().
Depending on this value, write the correct PLL register values and
calculate the correct pixel clock value.

Signed-off-by: Mathis Foerst <mathis.foerst@mt.com>
---
drivers/media/i2c/mt9m114.c | 33 ++++++++++++++++++++++++---------
1 file changed, 24 insertions(+), 9 deletions(-)

diff --git a/drivers/media/i2c/mt9m114.c b/drivers/media/i2c/mt9m114.c
index fa64d6d315a1..edbc0447141d 100644
--- a/drivers/media/i2c/mt9m114.c
+++ b/drivers/media/i2c/mt9m114.c
@@ -261,6 +261,7 @@
#define MT9M114_CAM_PGA_PGA_CONTROL CCI_REG16(0xc95e)
#define MT9M114_CAM_SYSCTL_PLL_ENABLE CCI_REG8(0xc97e)
#define MT9M114_CAM_SYSCTL_PLL_ENABLE_VALUE BIT(0)
+#define MT9M114_CAM_SYSCTL_PLL_DISABLE_VALUE 0x00
#define MT9M114_CAM_SYSCTL_PLL_DIVIDER_M_N CCI_REG16(0xc980)
#define MT9M114_CAM_SYSCTL_PLL_DIVIDER_VALUE(m, n) (((n) << 8) | (m))
#define MT9M114_CAM_SYSCTL_PLL_DIVIDER_P CCI_REG16(0xc982)
@@ -377,6 +378,7 @@ struct mt9m114 {
struct gpio_desc *reset;
struct regulator_bulk_data supplies[3];
struct v4l2_fwnode_endpoint bus_cfg;
+ bool bypass_pll;

struct {
unsigned int m;
@@ -743,14 +745,20 @@ static int mt9m114_initialize(struct mt9m114 *sensor)
}

/* Configure the PLL. */
- cci_write(sensor->regmap, MT9M114_CAM_SYSCTL_PLL_ENABLE,
- MT9M114_CAM_SYSCTL_PLL_ENABLE_VALUE, &ret);
- cci_write(sensor->regmap, MT9M114_CAM_SYSCTL_PLL_DIVIDER_M_N,
- MT9M114_CAM_SYSCTL_PLL_DIVIDER_VALUE(sensor->pll.m,
- sensor->pll.n),
- &ret);
- cci_write(sensor->regmap, MT9M114_CAM_SYSCTL_PLL_DIVIDER_P,
- MT9M114_CAM_SYSCTL_PLL_DIVIDER_P_VALUE(sensor->pll.p), &ret);
+ if (sensor->bypass_pll) {
+ cci_write(sensor->regmap, MT9M114_CAM_SYSCTL_PLL_ENABLE,
+ MT9M114_CAM_SYSCTL_PLL_DISABLE_VALUE, &ret);
+ } else {
+ cci_write(sensor->regmap, MT9M114_CAM_SYSCTL_PLL_ENABLE,
+ MT9M114_CAM_SYSCTL_PLL_ENABLE_VALUE, &ret);
+ cci_write(sensor->regmap, MT9M114_CAM_SYSCTL_PLL_DIVIDER_M_N,
+ MT9M114_CAM_SYSCTL_PLL_DIVIDER_VALUE(sensor->pll.m,
+ sensor->pll.n),
+ &ret);
+ cci_write(sensor->regmap, MT9M114_CAM_SYSCTL_PLL_DIVIDER_P,
+ MT9M114_CAM_SYSCTL_PLL_DIVIDER_P_VALUE(sensor->pll.p),
+ &ret);
+ }
cci_write(sensor->regmap, MT9M114_CAM_SENSOR_CFG_PIXCLK,
sensor->pixrate, &ret);

@@ -2268,8 +2276,12 @@ static int mt9m114_clk_init(struct mt9m114 *sensor)
* for 16-bit per pixel, transmitted in DDR over a single lane. For
* parallel mode, the sensor ouputs one pixel in two PIXCLK cycles.
*/
- sensor->pixrate = clk_get_rate(sensor->clk) * sensor->pll.m
+ if (sensor->bypass_pll) {
+ sensor->pixrate = clk_get_rate(sensor->clk) / 2;
+ } else {
+ sensor->pixrate = clk_get_rate(sensor->clk) * sensor->pll.m
/ ((sensor->pll.n + 1) * (sensor->pll.p + 1));
+ }

link_freq = sensor->bus_cfg.bus_type == V4L2_MBUS_CSI2_DPHY
? sensor->pixrate * 8 : sensor->pixrate * 2;
@@ -2321,6 +2333,7 @@ static int mt9m114_parse_dt(struct mt9m114 *sensor)
{
struct fwnode_handle *fwnode = dev_fwnode(&sensor->client->dev);
struct fwnode_handle *ep;
+ struct device_node *dev_node = sensor->client->dev.of_node;
int ret;

ep = fwnode_graph_get_next_endpoint(fwnode, NULL);
@@ -2349,6 +2362,8 @@ static int mt9m114_parse_dt(struct mt9m114 *sensor)
goto error;
}

+ sensor->bypass_pll = of_property_read_bool(dev_node, "bypass-pll");
+
return 0;

error:
--
2.34.1