Re: [PATCH 1/4] drm/i915/dsi: Fix pipe_bpp for handling for 6 bpc pixel-formats

[Jani Nikula <jani.nikula@linux.intel.com>]

On Sat, 01 Dec 2018, Hans de Goede <hdegoede@redhat.com> wrote:
> There are 3 problems with the dsi code's pipe_bpp handling for 6 bpc
> pixel-formats which this commit addresses:
>
> 1) It assumes that the pipe_bpp is the same as the bpp going over the dsi
> lanes. This assumption is not valid for MIPI_DSI_FMT_RGB666, where pipe_bpp
> should be 18 so that we do proper dithering but we actually send 24 bpp
> over the dsi lanes (MIPI_DSI_FMT_RGB666_PACKED sends 18 bpp).
>
> This assumption is enforced by an assert in *_dsi_get_pclk(). This assert
> triggers on the initial hw-state readback on BYT/CHT devices which use
> MIPI_DSI_FMT_RGB666, such as the Prowise PT301 tablet. PIPECONF is set to
> 6BPC / 18 bpp by the GOP, while mipi_dsi_pixel_format_to_bpp() returns 24.
>
> This commits switches the calculations in *_dsi_get_pclk() to use the bpp
> from mipi_dsi_pixel_format_to_bpp(intel_dsi->pixel_format) which
> returns the bpp going over the mipi lanes and drops the assert.
>
> 2) On BXT bxt_dsi_get_pipe_config() wrongly overrides the pipe_bpp which
> i9xx_get_pipe_config() reads from PIPECONF with the return value from
> mipi_dsi_pixel_format_to_bpp(). This avoids the assert from 1. but is wrong
> since the pipe is actually running at the value configured in PIPECONF.
>
> This commit drops the override of pipe_bpp from bxt_dsi_get_pipe_config().
>
> 3) The dsi encoder's compute_config() never assigns a value to pipe_bpp,
> unlike most other encoders. Falling back on compute_baseline_pipe_bpp()
> which always picks 24. 24 is only correct for MIPI_DSI_FMT_RGB88 for the
> others we should use 18 bpp so that we correctly do 6bpc color dithering.
>
> This commit adds code to intel_dsi_compute_config() to properly set
> pipe_bpp based on intel_dsi->pixel_format.
>
> Signed-off-by: Hans de Goede <hdegoede@redhat.com>
> ---
>  drivers/gpu/drm/i915/intel_dsi.h   |  4 ++--
>  drivers/gpu/drm/i915/vlv_dsi.c     | 17 ++++++++--------
>  drivers/gpu/drm/i915/vlv_dsi_pll.c | 31 ++++++------------------------
>  3 files changed, 17 insertions(+), 35 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/intel_dsi.h b/drivers/gpu/drm/i915/intel_dsi.h
> index c888c219835f..c796a2962a43 100644
> --- a/drivers/gpu/drm/i915/intel_dsi.h
> +++ b/drivers/gpu/drm/i915/intel_dsi.h
> @@ -160,7 +160,7 @@ int vlv_dsi_pll_compute(struct intel_encoder *encoder,
>  void vlv_dsi_pll_enable(struct intel_encoder *encoder,
>  			const struct intel_crtc_state *config);
>  void vlv_dsi_pll_disable(struct intel_encoder *encoder);
> -u32 vlv_dsi_get_pclk(struct intel_encoder *encoder, int pipe_bpp,
> +u32 vlv_dsi_get_pclk(struct intel_encoder *encoder,
>  		     struct intel_crtc_state *config);
>  void vlv_dsi_reset_clocks(struct intel_encoder *encoder, enum port port);
>  
> @@ -170,7 +170,7 @@ int bxt_dsi_pll_compute(struct intel_encoder *encoder,
>  void bxt_dsi_pll_enable(struct intel_encoder *encoder,
>  			const struct intel_crtc_state *config);
>  void bxt_dsi_pll_disable(struct intel_encoder *encoder);
> -u32 bxt_dsi_get_pclk(struct intel_encoder *encoder, int pipe_bpp,
> +u32 bxt_dsi_get_pclk(struct intel_encoder *encoder,
>  		     struct intel_crtc_state *config);
>  void bxt_dsi_reset_clocks(struct intel_encoder *encoder, enum port port);
>  
> diff --git a/drivers/gpu/drm/i915/vlv_dsi.c b/drivers/gpu/drm/i915/vlv_dsi.c
> index be3af5f6c7a0..c10def5efa22 100644
> --- a/drivers/gpu/drm/i915/vlv_dsi.c
> +++ b/drivers/gpu/drm/i915/vlv_dsi.c
> @@ -322,6 +322,11 @@ static bool intel_dsi_compute_config(struct intel_encoder *encoder,
>  	/* DSI uses short packets for sync events, so clear mode flags for DSI */
>  	adjusted_mode->flags = 0;
>  
> +	if (intel_dsi->pixel_format == MIPI_DSI_FMT_RGB888)
> +		pipe_config->pipe_bpp = 24;
> +	else
> +		pipe_config->pipe_bpp = 18;
> +
>  	if (IS_GEN9_LP(dev_priv)) {
>  		/* Enable Frame time stamp based scanline reporting */
>  		adjusted_mode->private_flags |=
> @@ -1097,10 +1102,8 @@ static void bxt_dsi_get_pipe_config(struct intel_encoder *encoder,
>  	}
>  
>  	fmt = I915_READ(MIPI_DSI_FUNC_PRG(port)) & VID_MODE_FORMAT_MASK;
> -	pipe_config->pipe_bpp =
> -			mipi_dsi_pixel_format_to_bpp(
> -				pixel_format_from_register_bits(fmt));

This part here was crucial for BXT/GLK hardware state readout. The CI
found it, but the result was ignored. :(

https://bugs.freedesktop.org/show_bug.cgi?id=109516

BR,
Jani.


> -	bpp = pipe_config->pipe_bpp;
> +	bpp = mipi_dsi_pixel_format_to_bpp(
> +			pixel_format_from_register_bits(fmt));
>  
>  	/* Enable Frame time stamo based scanline reporting */
>  	adjusted_mode->private_flags |=
> @@ -1238,11 +1241,9 @@ static void intel_dsi_get_config(struct intel_encoder *encoder,
>  
>  	if (IS_GEN9_LP(dev_priv)) {
>  		bxt_dsi_get_pipe_config(encoder, pipe_config);
> -		pclk = bxt_dsi_get_pclk(encoder, pipe_config->pipe_bpp,
> -					pipe_config);
> +		pclk = bxt_dsi_get_pclk(encoder, pipe_config);
>  	} else {
> -		pclk = vlv_dsi_get_pclk(encoder, pipe_config->pipe_bpp,
> -					pipe_config);
> +		pclk = vlv_dsi_get_pclk(encoder, pipe_config);
>  	}
>  
>  	if (pclk) {
> diff --git a/drivers/gpu/drm/i915/vlv_dsi_pll.c b/drivers/gpu/drm/i915/vlv_dsi_pll.c
> index a132a8037ecc..954d5a8c4fa7 100644
> --- a/drivers/gpu/drm/i915/vlv_dsi_pll.c
> +++ b/drivers/gpu/drm/i915/vlv_dsi_pll.c
> @@ -252,20 +252,12 @@ void bxt_dsi_pll_disable(struct intel_encoder *encoder)
>  		DRM_ERROR("Timeout waiting for PLL lock deassertion\n");
>  }
>  
> -static void assert_bpp_mismatch(enum mipi_dsi_pixel_format fmt, int pipe_bpp)
> -{
> -	int bpp = mipi_dsi_pixel_format_to_bpp(fmt);
> -
> -	WARN(bpp != pipe_bpp,
> -	     "bpp match assertion failure (expected %d, current %d)\n",
> -	     bpp, pipe_bpp);
> -}
> -
> -u32 vlv_dsi_get_pclk(struct intel_encoder *encoder, int pipe_bpp,
> +u32 vlv_dsi_get_pclk(struct intel_encoder *encoder,
>  		     struct intel_crtc_state *config)
>  {
>  	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
>  	struct intel_dsi *intel_dsi = enc_to_intel_dsi(&encoder->base);
> +	int bpp = mipi_dsi_pixel_format_to_bpp(intel_dsi->pixel_format);
>  	u32 dsi_clock, pclk;
>  	u32 pll_ctl, pll_div;
>  	u32 m = 0, p = 0, n;
> @@ -319,15 +311,12 @@ u32 vlv_dsi_get_pclk(struct intel_encoder *encoder, int pipe_bpp,
>  
>  	dsi_clock = (m * refclk) / (p * n);
>  
> -	/* pixel_format and pipe_bpp should agree */
> -	assert_bpp_mismatch(intel_dsi->pixel_format, pipe_bpp);
> -
> -	pclk = DIV_ROUND_CLOSEST(dsi_clock * intel_dsi->lane_count, pipe_bpp);
> +	pclk = DIV_ROUND_CLOSEST(dsi_clock * intel_dsi->lane_count, bpp);
>  
>  	return pclk;
>  }
>  
> -u32 bxt_dsi_get_pclk(struct intel_encoder *encoder, int pipe_bpp,
> +u32 bxt_dsi_get_pclk(struct intel_encoder *encoder,
>  		     struct intel_crtc_state *config)
>  {
>  	u32 pclk;
> @@ -335,12 +324,7 @@ u32 bxt_dsi_get_pclk(struct intel_encoder *encoder, int pipe_bpp,
>  	u32 dsi_ratio;
>  	struct intel_dsi *intel_dsi = enc_to_intel_dsi(&encoder->base);
>  	struct drm_i915_private *dev_priv = to_i915(encoder->base.dev);
> -
> -	/* Divide by zero */
> -	if (!pipe_bpp) {
> -		DRM_ERROR("Invalid BPP(0)\n");
> -		return 0;
> -	}
> +	int bpp = mipi_dsi_pixel_format_to_bpp(intel_dsi->pixel_format);
>  
>  	config->dsi_pll.ctrl = I915_READ(BXT_DSI_PLL_CTL);
>  
> @@ -348,10 +332,7 @@ u32 bxt_dsi_get_pclk(struct intel_encoder *encoder, int pipe_bpp,
>  
>  	dsi_clk = (dsi_ratio * BXT_REF_CLOCK_KHZ) / 2;
>  
> -	/* pixel_format and pipe_bpp should agree */
> -	assert_bpp_mismatch(intel_dsi->pixel_format, pipe_bpp);
> -
> -	pclk = DIV_ROUND_CLOSEST(dsi_clk * intel_dsi->lane_count, pipe_bpp);
> +	pclk = DIV_ROUND_CLOSEST(dsi_clk * intel_dsi->lane_count, bpp);
>  
>  	DRM_DEBUG_DRIVER("Calculated pclk=%u\n", pclk);
>  	return pclk;

-- 
Jani Nikula, Intel Open Source Graphics Center
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