[PATCH v5 13/13] drm/bridge: cdns-dsi: Use pre_enable/post_disable to enable/disable

[Dmitry Baryshkov]

On Sun, Oct 20, 2024 at 01:35:30AM +0530, Aradhya Bhatia wrote:
> From: Aradhya Bhatia <a-bhatia1 at ti.com>
> 
> The cdns-dsi controller requires that it be turned on completely before
> the input DPI's source has begun streaming[0]. Not having that, allows
> for a small window before cdns-dsi enable and after cdns-dsi disable
> where the previous entity (in this case tidss's videoport) to continue
> streaming DPI video signals. This small window where cdns-dsi is
> disabled but is still receiving signals causes the input FIFO of
> cdns-dsi to get corrupted. This causes the colors to shift on the output
> display. The colors can either shift by one color component (R->G, G->B,
> B->R), or by two color components (R->B, G->R, B->G).
> 
> Since tidss's videoport starts streaming via crtc enable hooks, we need
> cdns-dsi to be up and running before that. Now that the bridges are
> pre_enabled before crtc is enabled, and post_disabled after crtc is
> disabled, use the pre_enable and post_disable hooks to get cdns-dsi
> ready and running before the tidss videoport to get pass the color shift
> issues.
> 

Not being an expert in the TI DSS driver, would it be more proper to
handle that in the TI driver instead? I mean, sending out DPI signals
isn't a part of the CRTC setup, it's a job of the encoder.

> [0]: See section 12.6.5.7.3 "Start-up Procedure" in J721E SoC TRM
>      TRM Link: http://www.ti.com/lit/pdf/spruil1
> 
> Reviewed-by: Tomi Valkeinen <tomi.valkeinen at ideasonboard.com>
> Signed-off-by: Aradhya Bhatia <a-bhatia1 at ti.com>
> Signed-off-by: Aradhya Bhatia <aradhya.bhatia at linux.dev>
> ---
>  .../gpu/drm/bridge/cadence/cdns-dsi-core.c    | 62 ++++++++++---------
>  1 file changed, 34 insertions(+), 28 deletions(-)
> 
> diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> index 79d8c2264c14..dfeb53841ebc 100644
> --- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> +++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> @@ -658,13 +658,28 @@ cdns_dsi_bridge_mode_valid(struct drm_bridge *bridge,
>  	return MODE_OK;
>  }
>  
> -static void cdns_dsi_bridge_atomic_disable(struct drm_bridge *bridge,
> -					   struct drm_bridge_state *old_bridge_state)
> +static void cdns_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,
> +						struct drm_bridge_state *old_bridge_state)
>  {
>  	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
>  	struct cdns_dsi *dsi = input_to_dsi(input);
>  	u32 val;
>  
> +	/*
> +	 * The cdns-dsi controller needs to be disabled after it's DPI source
> +	 * has stopped streaming. If this is not followed, there is a brief
> +	 * window before DPI source is disabled and after cdns-dsi controller
> +	 * has been disabled where the DPI stream is still on, but the cdns-dsi
> +	 * controller is not ready anymore to accept the incoming signals. This
> +	 * is one of the reasons why a shift in pixel colors is observed on
> +	 * displays that have cdns-dsi as one of the bridges.
> +	 *
> +	 * To mitigate this, disable this bridge from the bridge post_disable()
> +	 * hook, instead of the bridge _disable() hook. The bridge post_disable()
> +	 * hook gets called after the CRTC disable, where often many DPI sources
> +	 * disable their streams.
> +	 */
> +
>  	val = readl(dsi->regs + MCTL_MAIN_DATA_CTL);
>  	val &= ~(IF_VID_SELECT_MASK | IF_VID_MODE | VID_EN | HOST_EOT_GEN |
>  		 DISP_EOT_GEN);
> @@ -683,15 +698,6 @@ static void cdns_dsi_bridge_atomic_disable(struct drm_bridge *bridge,
>  	pm_runtime_put(dsi->base.dev);
>  }
>  
> -static void cdns_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,
> -						struct drm_bridge_state *old_bridge_state)
> -{
> -	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
> -	struct cdns_dsi *dsi = input_to_dsi(input);
> -
> -	pm_runtime_put(dsi->base.dev);
> -}
> -
>  static void cdns_dsi_hs_init(struct cdns_dsi *dsi)
>  {
>  	struct cdns_dsi_output *output = &dsi->output;
> @@ -760,8 +766,8 @@ static void cdns_dsi_init_link(struct cdns_dsi *dsi)
>  	dsi->link_initialized = true;
>  }
>  
> -static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
> -					  struct drm_bridge_state *old_bridge_state)
> +static void cdns_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
> +					      struct drm_bridge_state *old_bridge_state)
>  {
>  	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
>  	struct cdns_dsi *dsi = input_to_dsi(input);
> @@ -776,6 +782,21 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
>  	if (WARN_ON(pm_runtime_get_sync(dsi->base.dev) < 0))
>  		return;
>  
> +	/*
> +	 * The cdns-dsi controller needs to be enabled before it's DPI source
> +	 * has begun streaming. If this is not followed, there is a brief window
> +	 * after DPI source enable and before cdns-dsi controller enable where
> +	 * the DPI stream is on, but the cdns-dsi controller is not ready to
> +	 * accept the incoming signals. This is one of the reasons why a shift
> +	 * in pixel colors is observed on displays that have cdns-dsi as one of
> +	 * the bridges.
> +	 *
> +	 * To mitigate this, enable this bridge from the bridge pre_enable()
> +	 * hook, instead of the bridge _enable() hook. The bridge pre_enable()
> +	 * hook gets called before the CRTC enable, where often many DPI sources
> +	 * enable their streams.
> +	 */
> +
>  	if (dsi->platform_ops && dsi->platform_ops->enable)
>  		dsi->platform_ops->enable(dsi);
>  
> @@ -912,19 +933,6 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
>  	writel(tmp, dsi->regs + MCTL_MAIN_EN);
>  }
>  
> -static void cdns_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
> -					      struct drm_bridge_state *old_bridge_state)
> -{
> -	struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
> -	struct cdns_dsi *dsi = input_to_dsi(input);
> -
> -	if (WARN_ON(pm_runtime_get_sync(dsi->base.dev) < 0))
> -		return;
> -
> -	cdns_dsi_init_link(dsi);
> -	cdns_dsi_hs_init(dsi);
> -}
> -
>  static u32 *cdns_dsi_bridge_get_input_bus_fmts(struct drm_bridge *bridge,
>  					       struct drm_bridge_state *bridge_state,
>  					       struct drm_crtc_state *crtc_state,
> @@ -968,9 +976,7 @@ static int cdns_dsi_bridge_atomic_check(struct drm_bridge *bridge,
>  static const struct drm_bridge_funcs cdns_dsi_bridge_funcs = {
>  	.attach = cdns_dsi_bridge_attach,
>  	.mode_valid = cdns_dsi_bridge_mode_valid,
> -	.atomic_disable = cdns_dsi_bridge_atomic_disable,
>  	.atomic_pre_enable = cdns_dsi_bridge_atomic_pre_enable,
> -	.atomic_enable = cdns_dsi_bridge_atomic_enable,
>  	.atomic_post_disable = cdns_dsi_bridge_atomic_post_disable,
>  	.atomic_check = cdns_dsi_bridge_atomic_check,
>  	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
> -- 
> 2.34.1
> 

-- 
With best wishes
Dmitry