Date: Wed, 26 Jun 2024 14:39:10 +0300
From: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>
To: Aradhya Bhatia <a-bhatia1@...com>,
 Dmitry Baryshkov <dmitry.baryshkov@...aro.org>,
 Andrzej Hajda <andrzej.hajda@...el.com>,
 Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>,
 Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
 Jonas Karlman <jonas@...boo.se>, Jernej Skrabec <jernej.skrabec@...il.com>,
 Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
 Maxime Ripard <mripard@...nel.org>, Jyri Sarha <jyri.sarha@....fi>,
 Thomas Zimmermann <tzimmermann@...e.de>, David Airlie <airlied@...il.com>,
 Daniel Vetter <daniel@...ll.ch>
Cc: DRI Development List <dri-devel@...ts.freedesktop.org>,
 Linux Kernel List <linux-kernel@...r.kernel.org>,
 Dominik Haller <d.haller@...tec.de>, Sam Ravnborg <sam@...nborg.org>,
 Thierry Reding <treding@...dia.com>,
 Kieran Bingham <kieran.bingham+renesas@...asonboard.com>,
 Nishanth Menon <nm@...com>, Vignesh Raghavendra <vigneshr@...com>,
 Praneeth Bajjuri <praneeth@...com>, Udit Kumar <u-kumar1@...com>,
 Devarsh Thakkar <devarsht@...com>, Jayesh Choudhary <j-choudhary@...com>,
 Jai Luthra <j-luthra@...com>
Subject: Re: [PATCH v4 11/11] drm/bridge: cdns-dsi: Use
 pre_enable/post_disable to enable/disable

On 22/06/2024 14:09, Aradhya Bhatia wrote:
> 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.
> 
> [0]: See section 12.6.5.7.3 "Start-up Procedure" in J721E SoC TRM
>       TRM Link: http://www.ti.com/lit/pdf/spruil1
> 

I think it makes sense to explain a bit about this in a comment in the 
driver code. Otherwise doing all of this in pre_enable and post_disable 
looks a bit odd.

Reviewed-by: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>

  Tomi

> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
> ---
>   .../gpu/drm/bridge/cadence/cdns-dsi-core.c    | 32 +++----------------
>   1 file changed, 4 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 c9697818308e..c352ea7db4ed 100644
> --- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> +++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
> @@ -655,8 +655,8 @@ 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);
> @@ -680,15 +680,6 @@ 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;
> @@ -757,8 +748,8 @@ 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);
> @@ -909,19 +900,6 @@ 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,
> @@ -952,9 +930,7 @@ static u32 *cdns_dsi_bridge_get_input_bus_fmts(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_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
>   	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,

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