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Date:   Mon, 15 Feb 2021 13:00:07 +0100
From:   Jacopo Mondi <jacopo@jmondi.org>
To:     Andrey Konovalov <andrey.konovalov@linaro.org>
Cc:     junak.pub@gmail.com, robert.foss@linaro.org,
        sakari.ailus@linux.intel.com, todor.too@gmail.com,
        agross@kernel.org, bjorn.andersson@linaro.org, mchehab@kernel.org,
        laurent.pinchart@ideasonboard.com, linux-media@vger.kernel.org,
        linux-arm-msm@vger.kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/2] media: camss: use v4l2_get_link_freq() to calculate
 the relevant clocks
Message-ID: <20210215120007.trtojpmq2wyknbuq@uno.localdomain>
References: <20210214213404.8373-1-andrey.konovalov@linaro.org>
 <20210214213404.8373-2-andrey.konovalov@linaro.org>
MIME-Version: 1.0
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In-Reply-To: <20210214213404.8373-2-andrey.konovalov@linaro.org>
Precedence: bulk

Hi Andrey,
   nice to see progress in this direction

On Mon, Feb 15, 2021 at 12:34:03AM +0300, Andrey Konovalov wrote:
> There are places in the camss driver where camss_get_pixel_clock() is
> called to get the pixel rate (using V4L2_CID_PIXEL_RATE control) and to
> calculate the link frequency from it. There is a case when this would
> not work: when V4L2_CID_PIXEL_RATE gets the rate at which the pixels are
> read (sampled) from the sensor's pixel array, and this rate is different
> from the pixel transmission rate over the CSI link, the link frequency
> value can't be calculated from the pixel rate. One needs to use
> V4L2_CID_LINK_FREQ to get the link frequency in this case.
>
> Replace such calls to camss_get_pixel_clock() with calls to a wrapper
> around v4l2_get_link_freq(). v4l2_get_link_freq() tries V4L2_CID_LINK_FREQ
> first, and if it is not implemented by the camera sensor driver, falls
> back to V4L2_CID_PIXEL_RATE to calculate the link frequency value from.

Is it worth warning in the core function that the subdevice should
support LINK_FREQ and if we fallback to use PIXEL_RATE the calculation
result might not be accurate ?

>
> Calls to camss_get_pixel_clock() from vfe_[check,set]_clock_rates()
> are left intact as it looks like this VFE clock does depend on the
> rate the pixel samples comes out of the camera sensor, not on the
> frequency at which the link between the sensor and the CSI receiver
> operates.
>
> Signed-off-by: Andrey Konovalov <andrey.konovalov@linaro.org>
> ---
>  .../media/platform/qcom/camss/camss-csid.c    | 22 ++++++------
>  .../qcom/camss/camss-csiphy-2ph-1-0.c         | 22 ++++++------
>  .../qcom/camss/camss-csiphy-3ph-1-0.c         | 22 ++++++------
>  .../media/platform/qcom/camss/camss-csiphy.c  | 36 +++++++++----------
>  .../media/platform/qcom/camss/camss-csiphy.h  |  2 +-
>  drivers/media/platform/qcom/camss/camss.c     | 23 ++++++++++++
>  drivers/media/platform/qcom/camss/camss.h     |  2 ++
>  7 files changed, 73 insertions(+), 56 deletions(-)
>
> diff --git a/drivers/media/platform/qcom/camss/camss-csid.c b/drivers/media/platform/qcom/camss/camss-csid.c
> index be3fe76f3dc3..b2cbf4b65949 100644
> --- a/drivers/media/platform/qcom/camss/camss-csid.c
> +++ b/drivers/media/platform/qcom/camss/camss-csid.c
> @@ -462,13 +462,19 @@ static irqreturn_t csid_isr(int irq, void *dev)
>  static int csid_set_clock_rates(struct csid_device *csid)
>  {
>  	struct device *dev = csid->camss->dev;
> -	u32 pixel_clock;
> +	s64 link_freq;
>  	int i, j;
>  	int ret;
>
> -	ret = camss_get_pixel_clock(&csid->subdev.entity, &pixel_clock);
> -	if (ret)
> -		pixel_clock = 0;
> +	const struct csid_format *f = csid_get_fmt_entry(
> +		csid->formats,
> +		csid->nformats,
> +		csid->fmt[MSM_CSIPHY_PAD_SINK].code);

Weird indent :/

I would either keep the arguments on one line or align after the open
( if it doesn't go past 80-cols


> +	u8 num_lanes = csid->phy.lane_cnt;
> +	link_freq = camss_get_link_freq(&csid->subdev.entity, f->bpp,

Empy line maybe ?

> +					2 * num_lanes);

I see you pass in 2 * num_lanes and I assume it's for CSI-2 DDR.
Can't this be handled in camss_get_link_freq() so that you here only
pass in the actual number of lanes ?
> +	if (link_freq < 0)
> +		link_freq = 0;

I don't know this driver, but I wonder if it wouldn't be better to
fail instead of defaulting to 0, which might be dangerous if used as a
divider.

>
>  	for (i = 0; i < csid->nclocks; i++) {
>  		struct camss_clock *clock = &csid->clock[i];
> @@ -477,13 +483,7 @@ static int csid_set_clock_rates(struct csid_device *csid)
>  		    !strcmp(clock->name, "csi1") ||
>  		    !strcmp(clock->name, "csi2") ||
>  		    !strcmp(clock->name, "csi3")) {
> -			const struct csid_format *f = csid_get_fmt_entry(
> -				csid->formats,
> -				csid->nformats,
> -				csid->fmt[MSM_CSIPHY_PAD_SINK].code);
> -			u8 num_lanes = csid->phy.lane_cnt;
> -			u64 min_rate = pixel_clock * f->bpp /
> -							(2 * num_lanes * 4);
> +			u64 min_rate = link_freq / 4;

Why 4 ? :)

>  			long rate;
>
>  			camss_add_clock_margin(&min_rate);
> diff --git a/drivers/media/platform/qcom/camss/camss-csiphy-2ph-1-0.c b/drivers/media/platform/qcom/camss/camss-csiphy-2ph-1-0.c
> index 12bce391d71f..30b454c369ab 100644
> --- a/drivers/media/platform/qcom/camss/camss-csiphy-2ph-1-0.c
> +++ b/drivers/media/platform/qcom/camss/camss-csiphy-2ph-1-0.c
> @@ -51,16 +51,13 @@ static void csiphy_reset(struct csiphy_device *csiphy)
>   *
>   * Helper function to calculate settle count value. This is
>   * based on the CSI2 T_hs_settle parameter which in turn
> - * is calculated based on the CSI2 transmitter pixel clock
> - * frequency.
> + * is calculated based on the CSI2 transmitter link frequency.
>   *
> - * Return settle count value or 0 if the CSI2 pixel clock
> - * frequency is not available
> + * Return settle count value or 0 if the CSI2 link frequency
> + * is not available
>   */
> -static u8 csiphy_settle_cnt_calc(u32 pixel_clock, u8 bpp, u8 num_lanes,
> -				 u32 timer_clk_rate)
> +static u8 csiphy_settle_cnt_calc(s64 link_freq, u32 timer_clk_rate)
>  {
> -	u32 mipi_clock; /* Hz */
>  	u32 ui; /* ps */
>  	u32 timer_period; /* ps */
>  	u32 t_hs_prepare_max; /* ps */
> @@ -68,8 +65,10 @@ static u8 csiphy_settle_cnt_calc(u32 pixel_clock, u8 bpp, u8 num_lanes,
>  	u32 t_hs_settle; /* ps */
>  	u8 settle_cnt;
>
> -	mipi_clock = pixel_clock * bpp / (2 * num_lanes);
> -	ui = div_u64(1000000000000LL, mipi_clock);
> +	if (link_freq <= 0)
> +		return 0;

If you error out if the link frequency cannot be calculated, can this
be skipped ?

> +
> +	ui = div_u64(1000000000000LL, link_freq);
>  	ui /= 2;
>  	t_hs_prepare_max = 85000 + 6 * ui;
>  	t_hs_prepare_zero_min = 145000 + 10 * ui;
> @@ -83,15 +82,14 @@ static u8 csiphy_settle_cnt_calc(u32 pixel_clock, u8 bpp, u8 num_lanes,
>
>  static void csiphy_lanes_enable(struct csiphy_device *csiphy,
>  				struct csiphy_config *cfg,
> -				u32 pixel_clock, u8 bpp, u8 lane_mask)
> +				s64 link_freq, u8 lane_mask)
>  {
>  	struct csiphy_lanes_cfg *c = &cfg->csi2->lane_cfg;
>  	u8 settle_cnt;
>  	u8 val, l = 0;
>  	int i = 0;
>
> -	settle_cnt = csiphy_settle_cnt_calc(pixel_clock, bpp, c->num_data,
> -					    csiphy->timer_clk_rate);
> +	settle_cnt = csiphy_settle_cnt_calc(link_freq, csiphy->timer_clk_rate);
>
>  	writel_relaxed(0x1, csiphy->base +
>  		       CAMSS_CSI_PHY_GLBL_T_INIT_CFG0);
> diff --git a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> index 97cb9de85031..da7c3d3f9a10 100644
> --- a/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> +++ b/drivers/media/platform/qcom/camss/camss-csiphy-3ph-1-0.c
> @@ -107,24 +107,23 @@ static irqreturn_t csiphy_isr(int irq, void *dev)
>   *
>   * Helper function to calculate settle count value. This is
>   * based on the CSI2 T_hs_settle parameter which in turn
> - * is calculated based on the CSI2 transmitter pixel clock
> - * frequency.
> + * is calculated based on the CSI2 transmitter link frequency.
>   *
> - * Return settle count value or 0 if the CSI2 pixel clock
> - * frequency is not available
> + * Return settle count value or 0 if the CSI2 link frequency
> + * is not available
>   */
> -static u8 csiphy_settle_cnt_calc(u32 pixel_clock, u8 bpp, u8 num_lanes,
> -				 u32 timer_clk_rate)
> +static u8 csiphy_settle_cnt_calc(s64 link_freq, u32 timer_clk_rate)
>  {
> -	u32 mipi_clock; /* Hz */
>  	u32 ui; /* ps */
>  	u32 timer_period; /* ps */
>  	u32 t_hs_prepare_max; /* ps */
>  	u32 t_hs_settle; /* ps */
>  	u8 settle_cnt;
>
> -	mipi_clock = pixel_clock * bpp / (2 * num_lanes);
> -	ui = div_u64(1000000000000LL, mipi_clock);
> +	if (link_freq <= 0)
> +		return 0;
> +
> +	ui = div_u64(1000000000000LL, link_freq);
>  	ui /= 2;
>  	t_hs_prepare_max = 85000 + 6 * ui;
>  	t_hs_settle = t_hs_prepare_max;
> @@ -137,15 +136,14 @@ static u8 csiphy_settle_cnt_calc(u32 pixel_clock, u8 bpp, u8 num_lanes,
>
>  static void csiphy_lanes_enable(struct csiphy_device *csiphy,
>  				struct csiphy_config *cfg,
> -				u32 pixel_clock, u8 bpp, u8 lane_mask)
> +				s64 link_freq, u8 lane_mask)
>  {
>  	struct csiphy_lanes_cfg *c = &cfg->csi2->lane_cfg;
>  	u8 settle_cnt;
>  	u8 val, l = 0;
>  	int i;
>
> -	settle_cnt = csiphy_settle_cnt_calc(pixel_clock, bpp, c->num_data,
> -					    csiphy->timer_clk_rate);
> +	settle_cnt = csiphy_settle_cnt_calc(link_freq, csiphy->timer_clk_rate);
>
>  	val = BIT(c->clk.pos);
>  	for (i = 0; i < c->num_data; i++)
> diff --git a/drivers/media/platform/qcom/camss/camss-csiphy.c b/drivers/media/platform/qcom/camss/camss-csiphy.c
> index 509c9a59c09c..9b5fe6fc7664 100644
> --- a/drivers/media/platform/qcom/camss/camss-csiphy.c
> +++ b/drivers/media/platform/qcom/camss/camss-csiphy.c
> @@ -102,23 +102,23 @@ static u8 csiphy_get_bpp(const struct csiphy_format *formats,
>  static int csiphy_set_clock_rates(struct csiphy_device *csiphy)
>  {
>  	struct device *dev = csiphy->camss->dev;
> -	u32 pixel_clock;
> +	s64 link_freq;
>  	int i, j;
>  	int ret;
>
> -	ret = camss_get_pixel_clock(&csiphy->subdev.entity, &pixel_clock);
> -	if (ret)
> -		pixel_clock = 0;
> +	u8 bpp = csiphy_get_bpp(csiphy->formats, csiphy->nformats,
> +				csiphy->fmt[MSM_CSIPHY_PAD_SINK].code);
> +	u8 num_lanes = csiphy->cfg.csi2->lane_cfg.num_data;
> +	link_freq = camss_get_link_freq(&csiphy->subdev.entity, bpp,
> +					2 * num_lanes);
> +	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]) {
> -			u8 bpp = csiphy_get_bpp(csiphy->formats,
> -					csiphy->nformats,
> -					csiphy->fmt[MSM_CSIPHY_PAD_SINK].code);
> -			u8 num_lanes = csiphy->cfg.csi2->lane_cfg.num_data;
> -			u64 min_rate = pixel_clock * bpp / (2 * num_lanes * 4);
> +			u64 min_rate = link_freq / 4;
>  			long round_rate;
>
>  			camss_add_clock_margin(&min_rate);
> @@ -238,22 +238,18 @@ static u8 csiphy_get_lane_mask(struct csiphy_lanes_cfg *lane_cfg)
>  static int csiphy_stream_on(struct csiphy_device *csiphy)
>  {
>  	struct csiphy_config *cfg = &csiphy->cfg;
> -	u32 pixel_clock;
> +	s64 link_freq;
>  	u8 lane_mask = csiphy_get_lane_mask(&cfg->csi2->lane_cfg);
>  	u8 bpp = csiphy_get_bpp(csiphy->formats, csiphy->nformats,
>  				csiphy->fmt[MSM_CSIPHY_PAD_SINK].code);
> +	u8 num_lanes = csiphy->cfg.csi2->lane_cfg.num_data;
>  	u8 val;
> -	int ret;
>
> -	ret = camss_get_pixel_clock(&csiphy->subdev.entity, &pixel_clock);
> -	if (ret) {
> -		dev_err(csiphy->camss->dev,
> -			"Cannot get CSI2 transmitter's pixel clock\n");
> -		return -EINVAL;
> -	}
> -	if (!pixel_clock) {
> +	link_freq = camss_get_link_freq(&csiphy->subdev.entity, bpp,
> +					2 * num_lanes);
> +	if (link_freq < 0) {
>  		dev_err(csiphy->camss->dev,
> -			"Got pixel clock == 0, cannot continue\n");
> +			"Cannot get CSI2 transmitter's link frequency\n");
>  		return -EINVAL;
>  	}
>
> @@ -268,7 +264,7 @@ static int csiphy_stream_on(struct csiphy_device *csiphy)
>  	writel_relaxed(val, csiphy->base_clk_mux);
>  	wmb();
>
> -	csiphy->ops->lanes_enable(csiphy, cfg, pixel_clock, bpp, lane_mask);
> +	csiphy->ops->lanes_enable(csiphy, cfg, link_freq, lane_mask);
>
>  	return 0;
>  }
> diff --git a/drivers/media/platform/qcom/camss/camss-csiphy.h b/drivers/media/platform/qcom/camss/camss-csiphy.h
> index f7967ef836dc..d71b8bc6ec00 100644
> --- a/drivers/media/platform/qcom/camss/camss-csiphy.h
> +++ b/drivers/media/platform/qcom/camss/camss-csiphy.h
> @@ -50,7 +50,7 @@ struct csiphy_hw_ops {
>  	void (*reset)(struct csiphy_device *csiphy);
>  	void (*lanes_enable)(struct csiphy_device *csiphy,
>  			     struct csiphy_config *cfg,
> -			     u32 pixel_clock, u8 bpp, u8 lane_mask);
> +			     s64 link_freq, u8 lane_mask);
>  	void (*lanes_disable)(struct csiphy_device *csiphy,
>  			      struct csiphy_config *cfg);
>  	irqreturn_t (*isr)(int irq, void *dev);
> diff --git a/drivers/media/platform/qcom/camss/camss.c b/drivers/media/platform/qcom/camss/camss.c
> index 7c0f669f8aa6..2888c7ef2303 100644
> --- a/drivers/media/platform/qcom/camss/camss.c
> +++ b/drivers/media/platform/qcom/camss/camss.c
> @@ -548,6 +548,29 @@ struct media_entity *camss_find_sensor(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
> + *
> + * 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)
> +{
> +	struct media_entity *sensor;
> +	struct v4l2_subdev *subdev;
> +
> +	sensor = camss_find_sensor(entity);
> +	if (!sensor)
> +		return -ENODEV;

Can this happen ?

Thanks
  j

> +
> +	subdev = media_entity_to_v4l2_subdev(sensor);
> +
> +	return v4l2_get_link_freq(subdev->ctrl_handler, bpp, lanes);
> +}
> +
>  /*
>   * camss_get_pixel_clock - Get pixel clock rate from sensor
>   * @entity: Media entity in the current pipeline
> diff --git a/drivers/media/platform/qcom/camss/camss.h b/drivers/media/platform/qcom/camss/camss.h
> index 3a0484683cd6..86cdc25189eb 100644
> --- a/drivers/media/platform/qcom/camss/camss.h
> +++ b/drivers/media/platform/qcom/camss/camss.h
> @@ -108,6 +108,8 @@ 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_entity *camss_find_sensor(struct media_entity *entity);
> +s64 camss_get_link_freq(struct media_entity *entity, unsigned int bpp,
> +			unsigned int lanes);
>  int camss_get_pixel_clock(struct media_entity *entity, u32 *pixel_clock);
>  int camss_pm_domain_on(struct camss *camss, int id);
>  void camss_pm_domain_off(struct camss *camss, int id);
> --
> 2.17.1
>