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Message-ID: <6cdc17f7-0926-4230-8be8-ecf26cc26df4@linaro.org>
Date: Sat, 17 Jan 2026 21:56:51 +0000
From: Bryan O'Donoghue <bryan.odonoghue@...aro.org>
To: david@...t.cz, Robert Foss <rfoss@...nel.org>,
Todor Tomov <todor.too@...il.com>,
Vladimir Zapolskiy <vladimir.zapolskiy@...aro.org>,
Mauro Carvalho Chehab <mchehab@...nel.org>,
Luca Weiss <luca.weiss@...rphone.com>, Petr Hodina <phodina@...tonmail.com>,
Casey Connolly <casey.connolly@...aro.org>, "Dr. Git" <drgitx@...il.com>
Cc: Konrad Dybcio <konrad.dybcio@....qualcomm.com>,
Joel Selvaraj <foss@...lselvaraj.com>, Kieran Bingham <kbingham@...nel.org>,
Sakari Ailus <sakari.ailus@...ux.intel.com>, linux-media@...r.kernel.org,
linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
phone-devel@...r.kernel.org
Subject: Re: [PATCH v3 8/8] media: qcom: camss: Account for C-PHY when
calculating link frequency
On 17/01/2026 15:36, David Heidelberg via B4 Relay wrote:
> From: David Heidelberg <david@...t.cz>
>
> 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@...ux.intel.com>
> Signed-off-by: David Heidelberg <david@...t.cz>
> ---
> drivers/media/platform/qcom/camss/camss-csid.c | 2 +-
> drivers/media/platform/qcom/camss/camss-csiphy.c | 6 ++++--
> drivers/media/platform/qcom/camss/camss.c | 16 +++++++++++++---
> drivers/media/platform/qcom/camss/camss.h | 2 +-
> 4 files changed, 19 insertions(+), 7 deletions(-)
>
> diff --git a/drivers/media/platform/qcom/camss/camss-csid.c b/drivers/media/platform/qcom/camss/camss-csid.c
> index b50b0cfe280c1..24f244d2959c9 100644
> --- a/drivers/media/platform/qcom/camss/camss-csid.c
> +++ b/drivers/media/platform/qcom/camss/camss-csid.c
> @@ -545,7 +545,7 @@ static int csid_set_clock_rates(struct csid_device *csid)
> 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);
> + csid->phy.lane_cnt, csid->phy.cphy);
Just pass &csid->phy ..
> if (link_freq < 0)
> link_freq = 0;
>
> diff --git a/drivers/media/platform/qcom/camss/camss-csiphy.c b/drivers/media/platform/qcom/camss/camss-csiphy.c
> index 08dd238e52799..1ea0d0ef354ff 100644
> --- a/drivers/media/platform/qcom/camss/camss-csiphy.c
> +++ b/drivers/media/platform/qcom/camss/camss-csiphy.c
> @@ -144,8 +144,9 @@ static int csiphy_set_clock_rates(struct csiphy_device *csiphy)
> 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;
> + 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);
CPHY shouldn't be a boolean special case - you have a use-case for the
containing structure, so pass that instead.
> if (link_freq < 0)
> link_freq = 0;
>
> @@ -270,9 +271,10 @@ static int csiphy_stream_on(struct csiphy_device *csiphy)
> 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;
> + 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,
> diff --git a/drivers/media/platform/qcom/camss/camss.c b/drivers/media/platform/qcom/camss/camss.c
> index ea0c8cf3cd806..556fedd92e065 100644
> --- a/drivers/media/platform/qcom/camss/camss.c
> +++ b/drivers/media/platform/qcom/camss/camss.c
> @@ -32,6 +32,14 @@
> #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[] = {
> @@ -4280,20 +4288,22 @@ 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
> + * @nr_of_lanes: Number of lanes in the link to the sensor
> *
> * 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 nr_of_lanes, bool cphy)
> {
> struct media_pad *sensor_pad;
> + unsigned int div = nr_of_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);
> }
>
> /*
> diff --git a/drivers/media/platform/qcom/camss/camss.h b/drivers/media/platform/qcom/camss/camss.h
> index 6d048414c919e..6bf7738837b89 100644
> --- a/drivers/media/platform/qcom/camss/camss.h
> +++ b/drivers/media/platform/qcom/camss/camss.h
> @@ -163,7 +163,7 @@ int camss_enable_clocks(int nclocks, struct camss_clock *clock,
> 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, 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);
>
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