Re: [PATCH RESEND v9 8/9] media: qcom: camss: Account for C-PHY when calculating link frequency

[Frank Li]

On Wed, Jul 29, 2026 at 10:20:03PM +0200, David Heidelberg wrote:
> Ensure that the link frequency divider correctly accounts for C-PHY
> operation. The divider differs between D-PHY and C-PHY, as described
> in the MIPI CSI-2 specification.
>
> For more details, see:
> https://docs.kernel.org/driver-api/media/tx-rx.html#pixel-rate
>
> Suggested-by: Sakari Ailus <sakari.ailus@xxxxxxxxxxxxxxx>
> Link: https://docs.kernel.org/driver-api/media/tx-rx.html#pixel-rate
> Signed-off-by: David Heidelberg <david@xxxxxxx>
> ---
>  drivers/media/platform/qcom/camss/camss-csid.c   |  6 ++++--
>  drivers/media/platform/qcom/camss/camss-csiphy.c |  6 ++++--
>  drivers/media/platform/qcom/camss/camss.c        | 15 +++++++++++++--
>  drivers/media/platform/qcom/camss/camss.h        |  2 +-
>  4 files changed, 22 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/media/platform/qcom/camss/camss-csid.c b/drivers/media/platform/qcom/camss/camss-csid.c
> index bcc34ac9dd212..c8cb6f1a3d3bc 100644
> --- a/drivers/media/platform/qcom/camss/camss-csid.c
> +++ b/drivers/media/platform/qcom/camss/camss-csid.c
> @@ -535,24 +535,26 @@ const struct csid_format_info *csid_get_fmt_entry(const struct csid_format_info
>  /*
>   * csid_set_clock_rates - Calculate and set clock rates on CSID module
>   * @csiphy: CSID device
>   */
>  static int csid_set_clock_rates(struct csid_device *csid)
>  {
>  	struct device *dev = csid->camss->dev;
>  	const struct csid_format_info *fmt;
> +	const bool cphy = (csid->phy.phy_sel == CSID_PHY_SEL_CPHY);
> +
>  	s64 link_freq;
>  	int i, j;
>  	int ret;
>
>  	fmt = csid_get_fmt_entry(csid->res->formats->formats, csid->res->formats->nformats,
>  				 csid->fmt[MSM_CSIPHY_PAD_SINK].code);
> -	link_freq = camss_get_link_freq(&csid->subdev.entity, fmt->bpp,
> -					csid->phy.lane_cnt);
> +
> +	link_freq = camss_get_link_freq(&csid->subdev.entity, fmt->bpp, csid->phy.lane_cnt, cphy);
>  	if (link_freq < 0)
>  		link_freq = 0;
>
>  	for (i = 0; i < csid->nclocks; i++) {
>  		struct camss_clock *clock = &csid->clock[i];
>
>  		if (!strcmp(clock->name, "csi0") ||
>  		    !strcmp(clock->name, "csi1") ||
> diff --git a/drivers/media/platform/qcom/camss/camss-csiphy.c b/drivers/media/platform/qcom/camss/camss-csiphy.c
> index 539ac4888b608..a136cd27880a6 100644
> --- a/drivers/media/platform/qcom/camss/camss-csiphy.c
> +++ b/drivers/media/platform/qcom/camss/camss-csiphy.c
> @@ -139,18 +139,19 @@ static int csiphy_set_clock_rates(struct csiphy_device *csiphy)
>  	struct device *dev = csiphy->camss->dev;
>  	s64 link_freq;
>  	int i, j;
>  	int ret;
>
>  	u8 bpp = csiphy_get_bpp(csiphy->res->formats->formats, csiphy->res->formats->nformats,
>  				csiphy->fmt[MSM_CSIPHY_PAD_SINK].code);
>  	u8 num_lanes = csiphy->cfg.csi2->lane_cfg.num_data;
> +	const bool cphy = (csiphy->cfg.csi2->lane_cfg.phy_cfg == V4L2_MBUS_CSI2_CPHY);
>
> -	link_freq = camss_get_link_freq(&csiphy->subdev.entity, bpp, num_lanes);
> +	link_freq = camss_get_link_freq(&csiphy->subdev.entity, bpp, num_lanes, cphy);
>  	if (link_freq < 0)
>  		link_freq  = 0;
>
>  	for (i = 0; i < csiphy->nclocks; i++) {
>  		struct camss_clock *clock = &csiphy->clock[i];
>
>  		if (csiphy->rate_set[i]) {
>  			u64 min_rate = link_freq / 4;
> @@ -265,19 +266,20 @@ static int csiphy_set_power(struct v4l2_subdev *sd, int on)
>  static int csiphy_stream_on(struct csiphy_device *csiphy)
>  {
>  	struct csiphy_config *cfg = &csiphy->cfg;
>  	s64 link_freq;
>  	u8 lane_mask = csiphy->res->hw_ops->get_lane_mask(&cfg->csi2->lane_cfg);
>  	u8 bpp = csiphy_get_bpp(csiphy->res->formats->formats, csiphy->res->formats->nformats,
>  				csiphy->fmt[MSM_CSIPHY_PAD_SINK].code);
>  	u8 num_lanes = csiphy->cfg.csi2->lane_cfg.num_data;
> +	const bool cphy = (csiphy->cfg.csi2->lane_cfg.phy_cfg == V4L2_MBUS_CSI2_CPHY);
>  	u8 val;
>
> -	link_freq = camss_get_link_freq(&csiphy->subdev.entity, bpp, num_lanes);
> +	link_freq = camss_get_link_freq(&csiphy->subdev.entity, bpp, num_lanes, cphy);
>
>  	if (link_freq < 0) {
>  		dev_err(csiphy->camss->dev,
>  			"Cannot get CSI2 transmitter's link frequency\n");
>  		return -EINVAL;
>  	}
>
>  	if (csiphy->base_clk_mux) {
> diff --git a/drivers/media/platform/qcom/camss/camss.c b/drivers/media/platform/qcom/camss/camss.c
> index 072c428e25166..66171069057f8 100644
> --- a/drivers/media/platform/qcom/camss/camss.c
> +++ b/drivers/media/platform/qcom/camss/camss.c
> @@ -27,16 +27,24 @@
>  #include <media/v4l2-mc.h>
>  #include <media/v4l2-fwnode.h>
>
>  #include "camss.h"
>
>  #define CAMSS_CLOCK_MARGIN_NUMERATOR 105
>  #define CAMSS_CLOCK_MARGIN_DENOMINATOR 100
>
> +/*
> + * C-PHY encodes data by 16/7 ~ 2.28 bits/symbol
> + * D-PHY doesn't encode data, thus 16/16 = 1 b/s
> + */
> +#define CAMSS_COMMON_PHY_DIVIDENT 16
> +#define CAMSS_CPHY_DIVISOR 7
> +#define CAMSS_DPHY_DIVISOR 16
> +
>  static const struct parent_dev_ops vfe_parent_dev_ops;
>
>  static const struct camss_subdev_resources csiphy_res_8x16[] = {
>  	/* CSIPHY0 */
>  	{
>  		.regulators = {},
>  		.clock = { "top_ahb", "ispif_ahb", "ahb", "csiphy0_timer" },
>  		.clock_rate = { { 0 },
> @@ -4619,29 +4627,32 @@ struct media_pad *camss_find_sensor_pad(struct media_entity *entity)
>  	}
>  }
>
>  /**
>   * camss_get_link_freq - Get link frequency from sensor
>   * @entity: Media entity in the current pipeline
>   * @bpp: Number of bits per pixel for the current format
>   * @lanes: Number of lanes in the link to the sensor
> + * @cphy: If C-PHY encoding is used.
>   *
>   * Return link frequency on success or a negative error code otherwise
>   */
>  s64 camss_get_link_freq(struct media_entity *entity, unsigned int bpp,
> -			unsigned int lanes)
> +			unsigned int lanes, const bool cphy)

you change this function argument, can you direct pass down csiphy instead
entity

so move
const bool cphy = (csiphy->cfg.csi2->lane_cfg.phy_cfg == V4L2_MBUS_CSI2_CPHY);

into this help function,

to avoid dupicate such logic everywhere.

Frank
>  {
>  	struct media_pad *sensor_pad;
> +	unsigned int div = lanes * 2 * (cphy ? CAMSS_CPHY_DIVISOR :
> +					       CAMSS_DPHY_DIVISOR);
>
>  	sensor_pad = camss_find_sensor_pad(entity);
>  	if (!sensor_pad)
>  		return -ENODEV;
>
> -	return v4l2_get_link_freq(sensor_pad, bpp, 2 * lanes);
> +	return v4l2_get_link_freq(sensor_pad, CAMSS_COMMON_PHY_DIVIDENT * bpp, div);
>  }
>
>  /*
>   * camss_get_pixel_clock - Get pixel clock rate from sensor
>   * @entity: Media entity in the current pipeline
>   * @pixel_clock: Received pixel clock value
>   *
>   * Return 0 on success or a negative error code otherwise
> diff --git a/drivers/media/platform/qcom/camss/camss.h b/drivers/media/platform/qcom/camss/camss.h
> index 93d691c8ac63b..12b14ba8fcec3 100644
> --- a/drivers/media/platform/qcom/camss/camss.h
> +++ b/drivers/media/platform/qcom/camss/camss.h
> @@ -164,17 +164,17 @@ struct parent_dev_ops {
>  };
>
>  void camss_add_clock_margin(u64 *rate);
>  int camss_enable_clocks(int nclocks, struct camss_clock *clock,
>  			struct device *dev);
>  void camss_disable_clocks(int nclocks, struct camss_clock *clock);
>  struct media_pad *camss_find_sensor_pad(struct media_entity *entity);
>  s64 camss_get_link_freq(struct media_entity *entity, unsigned int bpp,
> -			unsigned int lanes);
> +			unsigned int lanes, const bool cphy);
>  int camss_get_pixel_clock(struct media_entity *entity, u64 *pixel_clock);
>  int camss_pm_domain_on(struct camss *camss, int id);
>  void camss_pm_domain_off(struct camss *camss, int id);
>  int camss_vfe_get(struct camss *camss, int id);
>  void camss_vfe_put(struct camss *camss, int id);
>  void camss_delete(struct camss *camss);
>  void camss_buf_done(struct camss *camss, int hw_id, int port_id);
>  void camss_reg_update(struct camss *camss, int hw_id,
>
> --
> 2.53.0
>