[PATCH v10 13/13] drm/bridge: cdns-dsi: Use pre_enable/post_disable to enable/disable

Aradhya Bhatia
2025-02-26T15:58:17Z

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

Reviewed-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Tested-by: Tomi Valkeinen <tomi.valkeinen@ideasonboard.com>
Signed-off-by: Aradhya Bhatia <a-bhatia1@ti.com>
Signed-off-by: Aradhya Bhatia <aradhya.bhatia@linux.dev>
---
.../gpu/drm/bridge/cadence/cdns-dsi-core.c | 64 ++++++++++---------
1 file changed, 35 insertions(+), 29 deletions(-)

diff --git a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
index 93a238205169..8a320bd4d34d 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-dsi-core.c
@@ -669,13 +669,28 @@ 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_atomic_state *state)
+static void cdns_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,
+ struct drm_atomic_state *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);
@@ -687,15 +702,6 @@ static void cdns_dsi_bridge_atomic_disable(struct drm_bridge *bridge,
if (dsi->platform_ops && dsi->platform_ops->disable)
dsi->platform_ops->disable(dsi);

- pm_runtime_put(dsi->base.dev);
-}
-
-static void cdns_dsi_bridge_atomic_post_disable(struct drm_bridge *bridge,
- struct drm_atomic_state *state)
-{
- struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
- struct cdns_dsi *dsi = input_to_dsi(input);
-
dsi->phy_initialized = false;
dsi->link_initialized = false;
phy_power_off(dsi->dphy);
@@ -773,8 +779,8 @@ 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_atomic_state *state)
+static void cdns_dsi_bridge_atomic_pre_enable(struct drm_bridge *bridge,
+ struct drm_atomic_state *state)
{
struct cdns_dsi_input *input = bridge_to_cdns_dsi_input(bridge);
struct cdns_dsi *dsi = input_to_dsi(input);
@@ -788,6 +794,21 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
u32 tmp, reg_wakeup, div, status;
int nlanes;

+ /*
+ * 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 (WARN_ON(pm_runtime_get_sync(dsi->base.dev) < 0))
return;

@@ -804,8 +825,8 @@ static void cdns_dsi_bridge_atomic_enable(struct drm_bridge *bridge,
mode = &bridge->encoder->crtc->state->adjusted_mode;
nlanes = output->dev->lanes;

- cdns_dsi_hs_init(dsi);
cdns_dsi_init_link(dsi);
+ cdns_dsi_hs_init(dsi);

/*
* Now that the DSI Link and DSI Phy are initialized,
@@ -934,19 +955,6 @@ 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_atomic_state *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,
@@ -1041,9 +1049,7 @@ cdns_dsi_bridge_atomic_reset(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 = cdns_dsi_bridge_atomic_duplicate_state,
--
2.34.1