Re: [PATCH 1/4] drm/vc4: Adjust modes in DSI to work around the integer PLL divider.

[Daniel Vetter]

On Thu, May 11, 2017 at 04:56:22PM -0700, Eric Anholt wrote:
> BCM2835's PLLD_DSI1 divider doesn't give us many choices for our pixel
> clocks, so to support panels on the Raspberry Pi we need to set a
> higher pixel clock rate than requested and adjust the mode we program
> to extend out the HFP so that the refresh rate matches.
> 
> Signed-off-by: Eric Anholt <eric@xxxxxxxxxx>

Yeah, this is what mode_fixup is for (or the fancier atomic_check, but no
benefit with using that one here).

Acked-by: Daniel Vetter <daniel.vetter@xxxxxxxx>
> ---
>  drivers/gpu/drm/vc4/vc4_dsi.c | 112 ++++++++++++++++++++++++++++++++----------
>  1 file changed, 86 insertions(+), 26 deletions(-)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> index fb54a9d10360..62cb3b0d0345 100644
> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> @@ -519,7 +519,8 @@ struct vc4_dsi {
>  	/* DSI channel for the panel we're connected to. */
>  	u32 channel;
>  	u32 lanes;
> -	enum mipi_dsi_pixel_format format;
> +	u32 format;
> +	u32 divider;
>  	u32 mode_flags;
>  
>  	/* Input clock from CPRMAN to the digital PHY, for the DSI
> @@ -817,13 +818,67 @@ static void vc4_dsi_encoder_disable(struct drm_encoder *encoder)
>  	pm_runtime_put(dev);
>  }
>  
> +/* Extends the mode's blank intervals to handle BCM2835's integer-only
> + * DSI PLL divider.
> + *
> + * On 2835, PLLD is set to 2Ghz, and may not be changed by the display
> + * driver since most peripherals are hanging off of the PLLD_PER
> + * divider.  PLLD_DSI1, which drives our DSI bit clock (and therefore
> + * the pixel clock), only has an integer divider off of DSI.
> + *
> + * To get our panel mode to refresh at the expected 60Hz, we need to
> + * extend the horizontal blank time.  This means we drive a
> + * higher-than-expected clock rate to the panel, but that's what the
> + * firmware (which ) does too.
> + */
> +static bool vc4_dsi_encoder_mode_fixup(struct drm_encoder *encoder,
> +				       const struct drm_display_mode *mode,
> +				       struct drm_display_mode *adjusted_mode)
> +{
> +	struct vc4_dsi_encoder *vc4_encoder = to_vc4_dsi_encoder(encoder);
> +	struct vc4_dsi *dsi = vc4_encoder->dsi;
> +	struct clk *phy_parent = clk_get_parent(dsi->pll_phy_clock);
> +	unsigned long parent_rate = clk_get_rate(phy_parent);
> +	unsigned long pixel_clock_hz = mode->clock * 1000;
> +	unsigned long pll_clock = pixel_clock_hz * dsi->divider;
> +	int divider;
> +
> +	/* Find what divider gets us a faster clock than the requested
> +	 * pixel clock.
> +	 */
> +	for (divider = 1; divider < 8; divider++) {
> +		if (parent_rate / divider < pll_clock) {
> +			divider--;
> +			break;
> +		}
> +	}
> +
> +	/* Now that we've picked a PLL divider, calculate back to its
> +	 * pixel clock.
> +	 */
> +	pll_clock = parent_rate / divider;
> +	pixel_clock_hz = pll_clock / dsi->divider;
> +
> +	/* Round up the clk_set_rate() request slightly, since
> +	 * PLLD_DSI1 is an integer divider and its rate selection will
> +	 * never round up.
> +	 */
> +	adjusted_mode->clock = pixel_clock_hz / 1000 + 1;
> +
> +	/* Given the new pixel clock, adjust HFP to keep vrefresh the same. */
> +	adjusted_mode->htotal = pixel_clock_hz / (mode->vrefresh * mode->vtotal);
> +	adjusted_mode->hsync_end += adjusted_mode->htotal - mode->htotal;
> +	adjusted_mode->hsync_start += adjusted_mode->htotal - mode->htotal;
> +
> +	return true;
> +}
> +
>  static void vc4_dsi_encoder_enable(struct drm_encoder *encoder)
>  {
> -	struct drm_display_mode *mode = &encoder->crtc->mode;
> +	struct drm_display_mode *mode = &encoder->crtc->state->adjusted_mode;
>  	struct vc4_dsi_encoder *vc4_encoder = to_vc4_dsi_encoder(encoder);
>  	struct vc4_dsi *dsi = vc4_encoder->dsi;
>  	struct device *dev = &dsi->pdev->dev;
> -	u32 format = 0, divider = 0;
>  	bool debug_dump_regs = false;
>  	unsigned long hs_clock;
>  	u32 ui_ns;
> @@ -845,26 +900,7 @@ static void vc4_dsi_encoder_enable(struct drm_encoder *encoder)
>  		vc4_dsi_dump_regs(dsi);
>  	}
>  
> -	switch (dsi->format) {
> -	case MIPI_DSI_FMT_RGB888:
> -		format = DSI_PFORMAT_RGB888;
> -		divider = 24 / dsi->lanes;
> -		break;
> -	case MIPI_DSI_FMT_RGB666:
> -		format = DSI_PFORMAT_RGB666;
> -		divider = 24 / dsi->lanes;
> -		break;
> -	case MIPI_DSI_FMT_RGB666_PACKED:
> -		format = DSI_PFORMAT_RGB666_PACKED;
> -		divider = 18 / dsi->lanes;
> -		break;
> -	case MIPI_DSI_FMT_RGB565:
> -		format = DSI_PFORMAT_RGB565;
> -		divider = 16 / dsi->lanes;
> -		break;
> -	}
> -
> -	phy_clock = pixel_clock_hz * divider;
> +	phy_clock = pixel_clock_hz * dsi->divider;
>  	ret = clk_set_rate(dsi->pll_phy_clock, phy_clock);
>  	if (ret) {
>  		dev_err(&dsi->pdev->dev,
> @@ -1049,8 +1085,9 @@ static void vc4_dsi_encoder_enable(struct drm_encoder *encoder)
>  
>  	if (dsi->mode_flags & MIPI_DSI_MODE_VIDEO) {
>  		DSI_PORT_WRITE(DISP0_CTRL,
> -			       VC4_SET_FIELD(divider, DSI_DISP0_PIX_CLK_DIV) |
> -			       VC4_SET_FIELD(format, DSI_DISP0_PFORMAT) |
> +			       VC4_SET_FIELD(dsi->divider,
> +					     DSI_DISP0_PIX_CLK_DIV) |
> +			       VC4_SET_FIELD(dsi->format, DSI_DISP0_PFORMAT) |
>  			       VC4_SET_FIELD(DSI_DISP0_LP_STOP_PERFRAME,
>  					     DSI_DISP0_LP_STOP_CTRL) |
>  			       DSI_DISP0_ST_END |
> @@ -1255,9 +1292,31 @@ static int vc4_dsi_host_attach(struct mipi_dsi_host *host,
>  
>  	dsi->lanes = device->lanes;
>  	dsi->channel = device->channel;
> -	dsi->format = device->format;
>  	dsi->mode_flags = device->mode_flags;
>  
> +	switch (device->format) {
> +	case MIPI_DSI_FMT_RGB888:
> +		dsi->format = DSI_PFORMAT_RGB888;
> +		dsi->divider = 24 / dsi->lanes;
> +		break;
> +	case MIPI_DSI_FMT_RGB666:
> +		dsi->format = DSI_PFORMAT_RGB666;
> +		dsi->divider = 24 / dsi->lanes;
> +		break;
> +	case MIPI_DSI_FMT_RGB666_PACKED:
> +		dsi->format = DSI_PFORMAT_RGB666_PACKED;
> +		dsi->divider = 18 / dsi->lanes;
> +		break;
> +	case MIPI_DSI_FMT_RGB565:
> +		dsi->format = DSI_PFORMAT_RGB565;
> +		dsi->divider = 16 / dsi->lanes;
> +		break;
> +	default:
> +		dev_err(&dsi->pdev->dev, "Unknown DSI format: %d.\n",
> +			dsi->format);
> +		return 0;
> +	}
> +
>  	if (!(dsi->mode_flags & MIPI_DSI_MODE_VIDEO)) {
>  		dev_err(&dsi->pdev->dev,
>  			"Only VIDEO mode panels supported currently.\n");
> @@ -1304,6 +1363,7 @@ static const struct mipi_dsi_host_ops vc4_dsi_host_ops = {
>  static const struct drm_encoder_helper_funcs vc4_dsi_encoder_helper_funcs = {
>  	.disable = vc4_dsi_encoder_disable,
>  	.enable = vc4_dsi_encoder_enable,
> +	.mode_fixup = vc4_dsi_encoder_mode_fixup,
>  };
>  
>  static const struct of_device_id vc4_dsi_dt_match[] = {
> -- 
> 2.11.0
> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch