Re: [PATCH 06/21] media: ov5640: Rework CSI-2 clock tree

[Laurent Pinchart <laurent.pinchart@ideasonboard.com>]

Hi Jacopo,

Thank you for the patch.

On Mon, Jan 31, 2022 at 03:32:30PM +0100, Jacopo Mondi wrote:
> Re-work the ov5640_set_mipi_pclk() function to calculate the
> PLL configuration using the pixel_rate and link_freq values set at
> s_fmt time.
> 
> Rework the DVP clock mode settings to calculate the pixel clock
> internally and remove the assumption on the 16bpp format.
> 
> Tested in MIPI CSI-2 mode with 2 data lanes with:
> - all the sensor supported resolutions in UYVY and RGB565 formats.
> - resolutions >= 1280x720 in RAW Bayer format.
> - resolutions < 1280x720 in RGB888 format.
> 
> Signed-off-by: Jacopo Mondi <jacopo@jmondi.org>
> 
> ---
> 
> Not tested with JPEG.
> Not tested with 1 data lane.
> Not tested in DVP mode.
> 
> If I get come Tested-by: tags for the above use cases, it would be
> great.
> ---
>  drivers/media/i2c/ov5640.c | 175 ++++++++++++++++++++-----------------
>  1 file changed, 94 insertions(+), 81 deletions(-)
> 
> diff --git a/drivers/media/i2c/ov5640.c b/drivers/media/i2c/ov5640.c
> index 457f76030163..acc636500907 100644
> --- a/drivers/media/i2c/ov5640.c
> +++ b/drivers/media/i2c/ov5640.c
> @@ -29,6 +29,8 @@
>  #define OV5640_XCLK_MIN  6000000
>  #define OV5640_XCLK_MAX 54000000
>  
> +#define OV5640_LINK_RATE_MAX	490000000U
> +
>  #define OV5640_DEFAULT_SLAVE_ID 0x3c
>  
>  #define OV5640_REG_SYS_RESET02		0x3002
> @@ -88,6 +90,7 @@
>  #define OV5640_REG_POLARITY_CTRL00	0x4740
>  #define OV5640_REG_MIPI_CTRL00		0x4800
>  #define OV5640_REG_DEBUG_MODE		0x4814
> +#define OV5640_REG_PCLK_PERIOD		0x4837
>  #define OV5640_REG_ISP_FORMAT_MUX_CTRL	0x501f
>  #define OV5640_REG_PRE_ISP_TEST_SET1	0x503d
>  #define OV5640_REG_SDE_CTRL0		0x5580
> @@ -1035,69 +1038,80 @@ static unsigned long ov5640_calc_sys_clk(struct ov5640_dev *sensor,
>   * ov5640_set_mipi_pclk() - Calculate the clock tree configuration values
>   *			    for the MIPI CSI-2 output.
>   *
> - * @rate: The requested bandwidth per lane in bytes per second.
> - *	  'Bandwidth Per Lane' is calculated as:
> - *	  bpl = HTOT * VTOT * FPS * bpp / num_lanes;
> - *
> - * This function use the requested bandwidth to calculate:
> - * - sample_rate = bpl / (bpp / num_lanes);
> - *	         = bpl / (PLL_RDIV * BIT_DIV * PCLK_DIV * MIPI_DIV / num_lanes);
> - *
> - * - mipi_sclk   = bpl / MIPI_DIV / 2; ( / 2 is for CSI-2 DDR)

It would be useful to have the update formula either here or in the code
below.

> - *
> - * with these fixed parameters:
> - *	PLL_RDIV	= 2;
> - *	BIT_DIVIDER	= 2; (MIPI_BIT_MODE == 8 ? 2 : 2,5);
> - *	PCLK_DIV	= 1;
> - *
> - * The MIPI clock generation differs for modes that use the scaler and modes
> - * that do not. In case the scaler is in use, the MIPI_SCLK generates the MIPI
> - * BIT CLk, and thus:
> - *
> - * - mipi_sclk = bpl / MIPI_DIV / 2;
> - *   MIPI_DIV = 1;
> - *
> - * For modes that do not go through the scaler, the MIPI BIT CLOCK is generated
> - * from the pixel clock, and thus:
> - *
> - * - sample_rate = bpl / (bpp / num_lanes);
> - *	         = bpl / (2 * 2 * 1 * MIPI_DIV / num_lanes);
> - *		 = bpl / (4 * MIPI_DIV / num_lanes);
> - * - MIPI_DIV	 = bpp / (4 * num_lanes);
> - *
> - * FIXME: this have been tested with 16bpp and 2 lanes setup only.
> - * MIPI_DIV is fixed to value 2, but it -might- be changed according to the
> - * above formula for setups with 1 lane or image formats with different bpp.
> - *
> - * FIXME: this deviates from the sensor manual documentation which is quite
> - * thin on the MIPI clock tree generation part.
> + * FIXME: tested with 2 lanes only.
>   */
> -static int ov5640_set_mipi_pclk(struct ov5640_dev *sensor,
> -				unsigned long rate)
> +static int ov5640_set_mipi_pclk(struct ov5640_dev *sensor)
>  {
> -	const struct ov5640_mode_info *mode = sensor->current_mode;
> +	u8 bit_div, mipi_div, pclk_div, sclk_div, sclk2x_div, root_div;
> +	struct v4l2_mbus_framefmt *fmt = &sensor->fmt;
>  	u8 prediv, mult, sysdiv;
> -	u8 mipi_div;
> +	unsigned long sysclk;
> +	unsigned long sample_rate;
> +	u8 pclk_period;
> +	s64 link_freq;
>  	int ret;
>  
> +	/* Use the link frequency computed at s_fmt time. */
> +	link_freq = ov5640_csi2_link_freqs[sensor->ctrls.link_freq->cur.val];
> +
>  	/*
> -	 * 1280x720 is reported to use 'SUBSAMPLING' only,
> -	 * but according to the sensor manual it goes through the
> -	 * scaler before subsampling.
> +	 * - mipi_div - Additional divider for the MIPI lane clock.
> +	 *
> +	 * Higher link frequencies would make sysclk > 1GHz.
> +	 * Keep the sysclk low and do not divide in the MIPI domain.
>  	 */
> -	if (mode->dn_mode == SCALING ||
> -	   (mode->id == OV5640_MODE_720P_1280_720))
> -		mipi_div = OV5640_MIPI_DIV_SCLK;
> +	if (link_freq > OV5640_LINK_RATE_MAX)
> +		mipi_div = 1;
>  	else
> -		mipi_div = OV5640_MIPI_DIV_PCLK;
> +		mipi_div = 2;
>  
> -	ov5640_calc_sys_clk(sensor, rate, &prediv, &mult, &sysdiv);
> +	sysclk = link_freq * mipi_div;
> +	ov5640_calc_sys_clk(sensor, sysclk, &prediv, &mult, &sysdiv);
>  
> -	ret = ov5640_mod_reg(sensor, OV5640_REG_SC_PLL_CTRL0,
> -			     0x0f, OV5640_PLL_CTRL0_MIPI_MODE_8BIT);
> +	/*
> +	 * Adjust PLL parameters to maintain the MIPI_SCLK-to-PCLK ratio;
> +	 *
> +	 * - root_div = 2 (fixed)
> +	 * - bit_div : MIPI 8-bit = 2
> +	 *	       MIPI 10-bit = 2,5

s/2,5/2.5/

> +	 * - pclk_div = 1 (fixed)
> +	 * - pll_div  = (2 lanes ? mipi_div : 2 * mipi_div)

What's pll_div here ? There's no corresponding variable. It would be
nice to name it according to the clock tree diagram located above in the
driver.

> +	 *   2 lanes: MIPI_SCLK = (4 or 5) * PCLK
> +	 *   1 lanes: MIPI_SCLK = (8 or 10) * PCLK
> +	 *
> +	 * TODO: support 10-bit formats
> +	 * TODO: test with 1 data lane
> +	 */
> +	root_div = OV5640_PLL_CTRL3_PLL_ROOT_DIV_2;
> +	bit_div =  OV5640_PLL_CTRL0_MIPI_MODE_8BIT;
> +	pclk_div = OV5640_PLL_SYS_ROOT_DIVIDER_BYPASS;
>  
> -	ret = ov5640_mod_reg(sensor, OV5640_REG_SC_PLL_CTRL1,
> -			     0xff, sysdiv << 4 | mipi_div);
> +	/*
> +	 * Scaler clock:
> +	 * - YUV: PCLK >= 2 * SCLK
> +	 * - RAW or JPEG: PCLK >= SCLK
> +	 * - sclk2x_div = sclk_div / 2
> +	 *
> +	 * TODO: test with JPEG.
> +	 */
> +	sclk_div = ilog2(OV5640_SCLK_ROOT_DIV);
> +	sclk2x_div = ilog2(OV5640_SCLK2X_ROOT_DIV);
> +
> +	/*
> +	 * Set the sample period expressed in ns with 1-bit decimal
> +	 * (0x01=0.5ns).
> +	 */
> +	sample_rate = ov5640_pixel_rates[sensor->current_mode->pixel_rate]
> +		    * (ov5640_code_to_bpp(fmt->code) / 8);

Won't this cause rouding errors for bpp values that are not multiples of
8 ?

> +	pclk_period = 2000000000U / sample_rate;
> +
> +	/* Program the clock tree registers. */
> +	ret = ov5640_mod_reg(sensor, OV5640_REG_SC_PLL_CTRL0, 0x0f, bit_div);
> +	if (ret)
> +		return ret;
> +
> +	ret = ov5640_mod_reg(sensor, OV5640_REG_SC_PLL_CTRL1, 0xff,
> +			     sysdiv << 4 | mipi_div);

Here you don't use parentheses around (sysdiv << 4), and below you do
when writing OV5640_REG_SYS_ROOT_DIVIDER. They're not necessary, but it
could be clearer to add parentheses here.

>  	if (ret)
>  		return ret;
>  
> @@ -1105,13 +1119,27 @@ static int ov5640_set_mipi_pclk(struct ov5640_dev *sensor,
>  	if (ret)
>  		return ret;
>  
> -	ret = ov5640_mod_reg(sensor, OV5640_REG_SC_PLL_CTRL3,
> -			     0x1f, OV5640_PLL_CTRL3_PLL_ROOT_DIV_2 | prediv);
> +	ret = ov5640_mod_reg(sensor, OV5640_REG_SC_PLL_CTRL3, 0x1f,
> +			     root_div | prediv);
>  	if (ret)
>  		return ret;
>  
> -	return ov5640_mod_reg(sensor, OV5640_REG_SYS_ROOT_DIVIDER,
> -			      0x30, OV5640_PLL_SYS_ROOT_DIVIDER_BYPASS);
> +	ret = ov5640_mod_reg(sensor, OV5640_REG_SYS_ROOT_DIVIDER, 0x3f,
> +			     (pclk_div << 4) | (sclk2x_div << 2) | sclk_div);
> +	if (ret)
> +		return ret;
> +
> +	return ov5640_write_reg(sensor, OV5640_REG_PCLK_PERIOD, pclk_period);
> +}
> +
> +static u64 ov5640_calc_pixel_rate(struct ov5640_dev *sensor)
> +{
> +	u64 rate;
> +
> +	rate = sensor->current_mode->vtot * sensor->current_mode->htot;
> +	rate *= ov5640_framerates[sensor->current_fr];
> +
> +	return rate;
>  }
>  
>  static unsigned long ov5640_calc_pclk(struct ov5640_dev *sensor,
> @@ -1131,11 +1159,16 @@ static unsigned long ov5640_calc_pclk(struct ov5640_dev *sensor,
>  	return _rate / *pll_rdiv / *bit_div / *pclk_div;
>  }
>  
> -static int ov5640_set_dvp_pclk(struct ov5640_dev *sensor, unsigned long rate)
> +static int ov5640_set_dvp_pclk(struct ov5640_dev *sensor)
>  {
>  	u8 prediv, mult, sysdiv, pll_rdiv, bit_div, pclk_div;
> +	u64 rate;

Do you need a 64-bit integer here, or can the calculation fit in 32-bit?

>  	int ret;
>  
> +	rate = ov5640_calc_pixel_rate(sensor);
> +	rate *= ov5640_code_to_bpp(sensor->fmt.code);
> +	do_div(rate, sensor->ep.bus.parallel.bus_width);
> +
>  	ov5640_calc_pclk(sensor, rate, &prediv, &mult, &sysdiv, &pll_rdiv,
>  			 &bit_div, &pclk_div);
>  
> @@ -1660,16 +1693,6 @@ ov5640_find_mode(struct ov5640_dev *sensor, enum ov5640_frame_rate fr,
>  	return mode;
>  }
>  
> -static u64 ov5640_calc_pixel_rate(struct ov5640_dev *sensor)
> -{
> -	u64 rate;
> -
> -	rate = sensor->current_mode->vtot * sensor->current_mode->htot;
> -	rate *= ov5640_framerates[sensor->current_fr];
> -
> -	return rate;
> -}
> -
>  /*
>   * sensor changes between scaling and subsampling, go through
>   * exposure calculation
> @@ -1851,7 +1874,6 @@ static int ov5640_set_mode(struct ov5640_dev *sensor)
>  	enum ov5640_downsize_mode dn_mode, orig_dn_mode;
>  	bool auto_gain = sensor->ctrls.auto_gain->val == 1;
>  	bool auto_exp =  sensor->ctrls.auto_exp->val == V4L2_EXPOSURE_AUTO;
> -	unsigned long rate;
>  	int ret;
>  
>  	dn_mode = mode->dn_mode;
> @@ -1870,19 +1892,10 @@ static int ov5640_set_mode(struct ov5640_dev *sensor)
>  			goto restore_auto_gain;
>  	}
>  
> -	/*
> -	 * All the formats we support have 16 bits per pixel, seems to require
> -	 * the same rate than YUV, so we can just use 16 bpp all the time.
> -	 */
> -	rate = ov5640_calc_pixel_rate(sensor) * 16;
> -	if (ov5640_is_mipi(sensor)) {
> -		rate = rate / sensor->ep.bus.mipi_csi2.num_data_lanes;
> -		ret = ov5640_set_mipi_pclk(sensor, rate);
> -	} else {
> -		rate = rate / sensor->ep.bus.parallel.bus_width;
> -		ret = ov5640_set_dvp_pclk(sensor, rate);
> -	}
> -
> +	if (ov5640_is_mipi(sensor))
> +		ret = ov5640_set_mipi_pclk(sensor);
> +	else
> +		ret = ov5640_set_dvp_pclk(sensor);
>  	if (ret < 0)
>  		return 0;
>  

-- 
Regards,

Laurent Pinchart