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Message-ID: <m7t4hsa3lcszjbipxlypf655uspoxw3xfyy5jo3n3bnmqaiqcf@6wti5f477gve>
Date: Sun, 20 Oct 2024 14:57:33 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Aradhya Bhatia <aradhya.bhatia@...ux.dev>
Cc: Tomi Valkeinen <tomi.valkeinen@...asonboard.com>,
Laurent Pinchart <laurent.pinchart@...asonboard.com>, Andrzej Hajda <andrzej.hajda@...el.com>,
Neil Armstrong <neil.armstrong@...aro.org>, Robert Foss <rfoss@...nel.org>, Jonas Karlman <jonas@...boo.se>,
Jernej Skrabec <jernej.skrabec@...il.com>, Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
Maxime Ripard <mripard@...nel.org>, Thomas Zimmermann <tzimmermann@...e.de>,
David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
Dominik Haller <d.haller@...tec.de>, Sam Ravnborg <sam@...nborg.org>,
Kieran Bingham <kieran.bingham+renesas@...asonboard.com>, Nishanth Menon <nm@...com>,
Vignesh Raghavendra <vigneshr@...com>, Devarsh Thakkar <devarsht@...com>,
Praneeth Bajjuri <praneeth@...com>, Udit Kumar <u-kumar1@...com>,
Jayesh Choudhary <j-choudhary@...com>, DRI Development List <dri-devel@...ts.freedesktop.org>,
Linux Kernel List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v5 13/13] drm/bridge: cdns-dsi: Use
pre_enable/post_disable to enable/disable
On Sun, Oct 20, 2024 at 01:35:30AM +0530, Aradhya Bhatia wrote:
> From: Aradhya Bhatia <a-bhatia1@...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@...asonboard.com>
> Signed-off-by: Aradhya Bhatia <a-bhatia1@...com>
> Signed-off-by: Aradhya Bhatia <aradhya.bhatia@...ux.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
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