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

[David Heidelberg <david@ixit.cz>]

On 29/07/2026 23:41, Frank Li wrote:
> 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@linux.intel.com>
>> Link: https://docs.kernel.org/driver-api/media/tx-rx.html#pixel-rate
>> Signed-off-by: David Heidelberg <david@ixit.cz>
>> ---
>>   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.

I tried similar approach in previous revisions [1], but it ended poorly due to 
this structure not being initialized at the time when I need it what I recall, 
thus I ended up with the cphy param again :(

David


[1] https://lore.kernel.org/all/20260605-qcom-cphy-v7-7-426c37e9008f@ixit.cz/

> 
> 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
>>

-- 
David Heidelberg