9.1.15. MIPI CCS camera sensor driver

The MIPI CCS camera sensor driver is a generic driver for MIPI CCS compliant camera sensors. It exposes three sub-devices representing the pixel array, the binner and the scaler.

As the capabilities of individual devices vary, the driver exposes interfaces based on the capabilities that exist in hardware.

9.1.15.1. Pixel Array sub-device

The pixel array sub-device represents the camera sensor’s pixel matrix, as well as analogue crop functionality present in many compliant devices. The analogue crop is configured using the V4L2_SEL_TGT_CROP on the source pad (0) of the entity. The size of the pixel matrix can be obtained by getting the V4L2_SEL_TGT_NATIVE_SIZE target.

9.1.15.2. Binner

The binner sub-device represents the binning functionality on the sensor. For that purpose, selection target V4L2_SEL_TGT_COMPOSE is supported on the sink pad (0).

Additionally, if a device has no scaler or digital crop functionality, the source pad (1) expses another digital crop selection rectangle that can only crop at the end of the lines and frames.

9.1.15.3. Scaler

The scaler sub-device represents the digital crop and scaling functionality of the sensor. The V4L2 selection target V4L2_SEL_TGT_CROP is used to configure the digital crop on the sink pad (0) when digital crop is supported. Scaling is configured using selection target V4L2_SEL_TGT_COMPOSE on the sink pad (0) as well.

Additionally, if the scaler sub-device exists, its source pad (1) exposes another digital crop selection rectangle that can only crop at the end of the lines and frames.

9.1.15.4. Digital and analogue crop

Digital crop functionality is referred to as cropping that effectively works by dropping some data on the floor. Analogue crop, on the other hand, means that the cropped information is never retrieved. In case of camera sensors, the analogue data is never read from the pixel matrix that are outside the configured selection rectangle that designates crop. The difference has an effect in device timing and likely also in power consumption.

9.1.15.5. Register definition generator

The ccs-regs.asc file contains MIPI CCS register definitions that are used to produce C source code files for definitions that can be better used by programs written in C language. As there are many dependencies between the produced files, please do not modify them manually as it’s error-prone and in vain, but instead change the script producing them.

9.1.15.5.1. Usage

Conventionally the script is called this way to update the CCS driver definitions:

$ Documentation/driver-api/media/drivers/ccs/mk-ccs-regs -k \
        -e drivers/media/i2c/ccs/ccs-regs.h \
        -L drivers/media/i2c/ccs/ccs-limits.h \
        -l drivers/media/i2c/ccs/ccs-limits.c \
        -c Documentation/driver-api/media/drivers/ccs/ccs-regs.asc

9.1.16. CCS PLL calculator

The CCS PLL calculator is used to compute the PLL configuration, given sensor’s capabilities as well as board configuration and user specified configuration. As the configuration space that encompasses all these configurations is vast, the PLL calculator isn’t entirely trivial. Yet it is relatively simple to use for a driver.

The PLL model implemented by the PLL calculator corresponds to MIPI CCS 1.1.

struct ccs_pll_branch_fr

CCS PLL configuration (front)

Definition

struct ccs_pll_branch_fr {
  u16 pre_pll_clk_div;
  u16 pll_multiplier;
  u32 pll_ip_clk_freq_hz;
  u32 pll_op_clk_freq_hz;
};

Members

pre_pll_clk_div
Pre-PLL clock divisor
pll_multiplier
PLL multiplier
pll_ip_clk_freq_hz
PLL input clock frequency
pll_op_clk_freq_hz
PLL output clock frequency

Description

A single branch front-end of the CCS PLL tree.

struct ccs_pll_branch_bk

CCS PLL configuration (back)

Definition

struct ccs_pll_branch_bk {
  u16 sys_clk_div;
  u16 pix_clk_div;
  u32 sys_clk_freq_hz;
  u32 pix_clk_freq_hz;
};

Members

sys_clk_div
System clock divider
pix_clk_div
Pixel clock divider
sys_clk_freq_hz
System clock frequency
pix_clk_freq_hz
Pixel clock frequency

Description

A single branch back-end of the CCS PLL tree.

struct ccs_pll

Full CCS PLL configuration

Definition

struct ccs_pll {
  u8 bus_type;
  u8 op_lanes;
  u8 vt_lanes;
  struct {
    u8 lanes;
  } csi2;
  u8 binning_horizontal;
  u8 binning_vertical;
  u8 scale_m;
  u8 scale_n;
  u8 bits_per_pixel;
  u8 op_bits_per_lane;
  u16 flags;
  u32 link_freq;
  u32 ext_clk_freq_hz;
  struct ccs_pll_branch_fr vt_fr;
  struct ccs_pll_branch_bk vt_bk;
  struct ccs_pll_branch_fr op_fr;
  struct ccs_pll_branch_bk op_bk;
  u32 pixel_rate_csi;
  u32 pixel_rate_pixel_array;
};

Members

bus_type
Type of the data bus, CCS_PLL_BUS_TYPE_* (input)
op_lanes
Number of operational lanes (input)
vt_lanes
Number of video timing lanes (input)
csi2
CSI-2 related parameters
csi2.lanes
The number of the CSI-2 data lanes (input)
binning_horizontal
Horizontal binning factor (input)
binning_vertical
Vertical binning factor (input)
scale_m
Downscaling factor, M component, [16, max] (input)
scale_n
Downscaling factor, N component, typically 16 (input)
bits_per_pixel
Bits per pixel on the output data bus (input)
op_bits_per_lane
Number of bits per OP lane (input)
flags
CCS_PLL_FLAG_* (input)
link_freq
Chosen link frequency (input)
ext_clk_freq_hz
External clock frequency, i.e. the sensor’s input clock (input)
vt_fr
Video timing front-end configuration (output)
vt_bk
Video timing back-end configuration (output)
op_fr
Operational timing front-end configuration (output)
op_bk
Operational timing back-end configuration (output)
pixel_rate_csi
Pixel rate on the output data bus (output)
pixel_rate_pixel_array
Nominal pixel rate in the sensor’s pixel array (output)

Description

All information required to calculate CCS PLL configuration.

struct ccs_pll_branch_limits_fr

CCS PLL front-end limits

Definition

struct ccs_pll_branch_limits_fr {
  u16 min_pre_pll_clk_div;
  u16 max_pre_pll_clk_div;
  u32 min_pll_ip_clk_freq_hz;
  u32 max_pll_ip_clk_freq_hz;
  u16 min_pll_multiplier;
  u16 max_pll_multiplier;
  u32 min_pll_op_clk_freq_hz;
  u32 max_pll_op_clk_freq_hz;
};

Members

min_pre_pll_clk_div
Minimum pre-PLL clock divider
max_pre_pll_clk_div
Maximum pre-PLL clock divider
min_pll_ip_clk_freq_hz
Minimum PLL input clock frequency
max_pll_ip_clk_freq_hz
Maximum PLL input clock frequency
min_pll_multiplier
Minimum PLL multiplier
max_pll_multiplier
Maximum PLL multiplier
min_pll_op_clk_freq_hz
Minimum PLL output clock frequency
max_pll_op_clk_freq_hz
Maximum PLL output clock frequency
struct ccs_pll_branch_limits_bk

CCS PLL back-end limits

Definition

struct ccs_pll_branch_limits_bk {
  u16 min_sys_clk_div;
  u16 max_sys_clk_div;
  u32 min_sys_clk_freq_hz;
  u32 max_sys_clk_freq_hz;
  u16 min_pix_clk_div;
  u16 max_pix_clk_div;
  u32 min_pix_clk_freq_hz;
  u32 max_pix_clk_freq_hz;
};

Members

min_sys_clk_div
Minimum system clock divider
max_sys_clk_div
Maximum system clock divider
min_sys_clk_freq_hz
Minimum system clock frequency
max_sys_clk_freq_hz
Maximum system clock frequency
min_pix_clk_div
Minimum pixel clock divider
max_pix_clk_div
Maximum pixel clock divider
min_pix_clk_freq_hz
Minimum pixel clock frequency
max_pix_clk_freq_hz
Maximum pixel clock frequency
struct ccs_pll_limits

CCS PLL limits

Definition

struct ccs_pll_limits {
  u32 min_ext_clk_freq_hz;
  u32 max_ext_clk_freq_hz;
  struct ccs_pll_branch_limits_fr vt_fr;
  struct ccs_pll_branch_limits_bk vt_bk;
  struct ccs_pll_branch_limits_fr op_fr;
  struct ccs_pll_branch_limits_bk op_bk;
  u32 min_line_length_pck_bin;
  u32 min_line_length_pck;
};

Members

min_ext_clk_freq_hz
Minimum external clock frequency
max_ext_clk_freq_hz
Maximum external clock frequency
vt_fr
Video timing front-end limits
vt_bk
Video timing back-end limits
op_fr
Operational timing front-end limits
op_bk
Operational timing back-end limits
min_line_length_pck_bin
Minimum line length in pixels, with binning
min_line_length_pck
Minimum line length in pixels without binning
int ccs_pll_calculate(struct device *dev, const struct ccs_pll_limits *limits, struct ccs_pll *pll)

Calculate CCS PLL configuration based on input parameters

Parameters

struct device *dev
Device pointer, used for printing messages
const struct ccs_pll_limits *limits
Limits specific to the sensor
struct ccs_pll *pll
Given PLL configuration

Description

Calculate the CCS PLL configuration based on the limits as well as given device specific, system specific or user configured input data.

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