[PATCH] drm/mediatek: dsi: Fix DSI host and panel bridge pre-enable order

[Louis-Alexis Eyraud]

Since commit c9b1150a68d9 ("drm/atomic-helper: Re-order bridge chain
pre-enable and post-disable"), the bridge pre_enable callbacks are now
called before crtc enable, and the bridge post_disable callbacks after
the crtc disable.
In the mediatek-drm driver, this change leads to transfer errors on
mtk_dsi_host_transfer callback processing during the panel bridge
pre-enable sequence because the DSI host bridge pre_enable and CRTC
enable sequences, that are enabling the required clocks and PHY using
mtk_dsi_poweron function, are called after.

So, in order to fix this call order issue, request the DSI host bridge
be pre-enabled before panel bridge by setting pre_enable_prev_first
flag on DSI device bridge in the mtk_dsi_host_attach function.

Fixes: c9b1150a68d9 ("drm/atomic-helper: Re-order bridge chain pre-enable and post-disable")
Signed-off-by: Louis-Alexis Eyraud <louisalexis.eyraud at collabora.com>
---
This patch fixes an issue that can be observed on boards such as
MediatekGenio 1200-EVK or 350-EVK with a kernel based on linux-next
(tag: next-20250635) since commit c9b1150a68d9 ("drm/atomic-helper:
Re-order bridge chain pre-enable and post-disable"). 
In boot logs, there are multiples errors such as IRQ timeouts and
panel init errors, leading the DSI panel not being enabled: 

Example on Genio 1200-EVK:
```
[drm] Wait DSI IRQ(0x00000002) Timeout
panel-himax-hx8279 1c008000.dsi.0: sending generic data b0 05 failed:
  -62
[drm] Wait DSI IRQ(0x00000008) Timeout
[drm:mtk_dsi_host_transfer [mediatek_drm]] *ERROR* failed to switch cmd
 mode
panel-himax-hx8279 1c008000.dsi.0: sending DCS SET_DISPLAY_ON failed:
  -62
```
---
 drivers/gpu/drm/mediatek/mtk_dsi.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
index d7726091819c4762698b41060b3d4d8d27940238..0e2bcd5f67b767d92f2697a5b8183f67ee178a38 100644
--- a/drivers/gpu/drm/mediatek/mtk_dsi.c
+++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
@@ -1002,6 +1002,12 @@ static int mtk_dsi_host_attach(struct mipi_dsi_host *host,
 			return PTR_ERR(dsi->next_bridge);
 	}
 
+	/*
+	 * set flag to request the DSI host bridge be pre-enabled before device bridge
+	 * in the chain, so the DSI host is ready when the device bridge is pre-enabled
+	 */
+	dsi->next_bridge->pre_enable_prev_first = true;
+
 	drm_bridge_add(&dsi->bridge);
 
 	ret = component_add(host->dev, &mtk_dsi_component_ops);

---
base-commit: c6a68d8f7b81a6ce8962885408cc2d0c1f8b9470
change-id: 20250630-mediatek-drm-fix-dsi-panel-init-1a4b534c40a6

Best regards,
-- 
Louis-Alexis Eyraud <louisalexis.eyraud at collabora.com>