Subject: [PATCH v3 16/24] drm/rockchip: dw-mipi-dsi: properly configure PHY timing

From: [email-masked] (Sean Paul)
Date: Mon, 30 Jan 2017 16:57:36 -0500

On Sun, Jan 29, 2017 at 01:24:36PM +0000, John Keeping wrote:
> These values are specified as constant time periods but the PHY
> configuration is in terms of the current lane byte clock so using
> constant values guarantees that the timings will be outside the
> specification with some display configurations.
> 
> Derive the necessary configuration from the byte clock in order to
> ensure that the PHY configuration is correct.
> 
> Signed-off-by: John Keeping <[email-masked]>
> ---
> v3:
> - Wrap some long lines
> Unchanged in v2
> 
>  drivers/gpu/drm/rockchip/dw-mipi-dsi.c | 39 ++++++++++++++++++++++++++++++----
>  1 file changed, 35 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> index cfe7e4ba305c..85edf6dd2bac 100644
> --- a/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> +++ b/drivers/gpu/drm/rockchip/dw-mipi-dsi.c
> @@ -383,6 +383,26 @@ static void dw_mipi_dsi_phy_write(struct dw_mipi_dsi *dsi, u8 test_code,
>  	dsi_write(dsi, DSI_PHY_TST_CTRL0, PHY_TESTCLK | PHY_UNTESTCLR);
>  }
>  
> +/**
> + * ns2bc - Nanoseconds to byte clock cycles
> + */
> +static inline unsigned int ns2bc(struct dw_mipi_dsi *dsi, int ns)
> +{
> +	unsigned long byte_clk_khz = dsi->lane_mbps * MSEC_PER_SEC / 8;

Why multiply by 1000 (MSEC_PER_SEC) only to immediately divide by 1000?

> +
> +	return (ns * (byte_clk_khz / 1000) + 999) / 1000;

Can you replace this whole function with:

return DIV_ROUND_UP(ns * dsi->lane_mbps / 8, 1000);

> +}
> +
> +/**
> + * ns2ui - Nanoseconds to UI time periods
> + */
> +static inline unsigned int ns2ui(struct dw_mipi_dsi *dsi, int ns)
> +{
> +	unsigned long byte_clk_khz = dsi->lane_mbps * MSEC_PER_SEC;
> +
> +	return (ns * (byte_clk_khz / 1000) + 999) / 1000;

Same remarks here.

Sean

> +}
> +
>  static int dw_mipi_dsi_phy_init(struct dw_mipi_dsi *dsi)
>  {
>  	int ret, testdin, vco, val;
> @@ -434,10 +454,21 @@ static int dw_mipi_dsi_phy_init(struct dw_mipi_dsi *dsi)
>  					 SETRD_MAX | POWER_MANAGE |
>  					 TER_RESISTORS_ON);
>  
> -
> -	dw_mipi_dsi_phy_write(dsi, 0x70, TLP_PROGRAM_EN | 0xf);
> -	dw_mipi_dsi_phy_write(dsi, 0x71, THS_PRE_PROGRAM_EN | 0x55);
> -	dw_mipi_dsi_phy_write(dsi, 0x72, THS_ZERO_PROGRAM_EN | 0xa);
> +	dw_mipi_dsi_phy_write(dsi, 0x60, TLP_PROGRAM_EN | ns2bc(dsi, 500));
> +	dw_mipi_dsi_phy_write(dsi, 0x61, THS_PRE_PROGRAM_EN | ns2ui(dsi, 40));
> +	dw_mipi_dsi_phy_write(dsi, 0x62, THS_ZERO_PROGRAM_EN | ns2bc(dsi, 300));
> +	dw_mipi_dsi_phy_write(dsi, 0x63, THS_PRE_PROGRAM_EN | ns2ui(dsi, 100));
> +	dw_mipi_dsi_phy_write(dsi, 0x64, BIT(5) | ns2bc(dsi, 100));
> +	dw_mipi_dsi_phy_write(dsi, 0x65, BIT(5) | (ns2bc(dsi, 60) + 7));
> +
> +	dw_mipi_dsi_phy_write(dsi, 0x70, TLP_PROGRAM_EN | ns2bc(dsi, 500));
> +	dw_mipi_dsi_phy_write(dsi, 0x71,
> +			      THS_PRE_PROGRAM_EN | (ns2ui(dsi, 50) + 5));
> +	dw_mipi_dsi_phy_write(dsi, 0x72,
> +			      THS_ZERO_PROGRAM_EN | (ns2bc(dsi, 140) + 2));
> +	dw_mipi_dsi_phy_write(dsi, 0x73,
> +			      THS_PRE_PROGRAM_EN | (ns2ui(dsi, 60) + 8));
> +	dw_mipi_dsi_phy_write(dsi, 0x74, BIT(5) | ns2bc(dsi, 100));
>  
>  	dsi_write(dsi, DSI_PHY_RSTZ, PHY_ENFORCEPLL | PHY_ENABLECLK |
>  				     PHY_UNRSTZ | PHY_UNSHUTDOWNZ);
> -- 
> 2.11.0.197.gb556de5.dirty
> 
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-- 
Sean Paul, Software Engineer, Google / Chromium OS