[PATCH v2] drm/mediatek: dsi: Store driver data before invoking mipi_dsi_host_register

[PATCH v2] drm/mediatek: dsi: Store driver data before invoking mipi_dsi_host_register

[Luca Leonardo Scorcia]

The call to mipi_dsi_host_register triggers a callback to mtk_dsi_bind,
which uses dev_get_drvdata to retrieve the mtk_dsi struct, so this
structure needs to be stored inside the driver data before invoking it.

As drvdata is currently uninitialized it leads to a crash when
registering the DSI DRM encoder right after acquiring
the mode_config.idr_mutex, blocking all subsequent DRM operations.

Fixes the following crash during mediatek-drm probe (tested on Xiaomi
Smart Clock x04g):

Unable to handle kernel NULL pointer dereference at virtual address
 0000000000000040
[...]
Modules linked in: mediatek_drm(+) drm_display_helper cec drm_client_lib
 drm_dma_helper drm_kms_helper panel_simple
[...]
Call trace:
 drm_mode_object_add+0x58/0x98 (P)
 __drm_encoder_init+0x48/0x140
 drm_encoder_init+0x6c/0xa0
 drm_simple_encoder_init+0x20/0x34 [drm_kms_helper]
 mtk_dsi_bind+0x34/0x13c [mediatek_drm]
 component_bind_all+0x120/0x280
 mtk_drm_bind+0x284/0x67c [mediatek_drm]
 try_to_bring_up_aggregate_device+0x23c/0x320
 __component_add+0xa4/0x198
 component_add+0x14/0x20
 mtk_dsi_host_attach+0x78/0x100 [mediatek_drm]
 mipi_dsi_attach+0x2c/0x50
 panel_simple_dsi_probe+0x4c/0x9c [panel_simple]
 mipi_dsi_drv_probe+0x1c/0x28
 really_probe+0xc0/0x3dc
 __driver_probe_device+0x80/0x160
 driver_probe_device+0x40/0x120
 __device_attach_driver+0xbc/0x17c
 bus_for_each_drv+0x88/0xf0
 __device_attach+0x9c/0x1cc
 device_initial_probe+0x54/0x60
 bus_probe_device+0x34/0xa0
 device_add+0x5b0/0x800
 mipi_dsi_device_register_full+0xdc/0x16c
 mipi_dsi_host_register+0xc4/0x17c
 mtk_dsi_probe+0x10c/0x260 [mediatek_drm]
 platform_probe+0x5c/0xa4
 really_probe+0xc0/0x3dc
 __driver_probe_device+0x80/0x160
 driver_probe_device+0x40/0x120
 __driver_attach+0xc8/0x1f8
 bus_for_each_dev+0x7c/0xe0
 driver_attach+0x24/0x30
 bus_add_driver+0x11c/0x240
 driver_register+0x68/0x130
 __platform_register_drivers+0x64/0x160
 mtk_drm_init+0x24/0x1000 [mediatek_drm]
 do_one_initcall+0x60/0x1d0
 do_init_module+0x54/0x240
 load_module+0x1838/0x1dc0
 init_module_from_file+0xd8/0xf0
 __arm64_sys_finit_module+0x1b4/0x428
 invoke_syscall.constprop.0+0x48/0xc8
 do_el0_svc+0x3c/0xb8
 el0_svc+0x34/0xe8
 el0t_64_sync_handler+0xa0/0xe4
 el0t_64_sync+0x198/0x19c
Code: 52800022 941004ab 2a0003f3 37f80040 (29005a80)
---[ end trace 0000000000000000 ]---

Fixes: e4732b590a77 ("drm/mediatek: dsi: Register DSI host after acquiring clocks and PHY")
Signed-off-by: Luca Leonardo Scorcia <l.scorcia@gmail.com>
Reviewed-by: AngeloGioacchino Del Regno <angelogioacchino.delregno@collabora.com>
---
v2: Added Fixes tag

 drivers/gpu/drm/mediatek/mtk_dsi.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
index d7726091819c..af4871de9e4c 100644
--- a/drivers/gpu/drm/mediatek/mtk_dsi.c
+++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
@@ -1232,6 +1232,8 @@ static int mtk_dsi_probe(struct platform_device *pdev)
 
 	dsi->host.ops = &mtk_dsi_ops;
 	dsi->host.dev = dev;
+	platform_set_drvdata(pdev, dsi);
+
 	ret = mipi_dsi_host_register(&dsi->host);
 	if (ret < 0)
 		return dev_err_probe(dev, ret, "Failed to register DSI host\n");
@@ -1245,8 +1247,6 @@ static int mtk_dsi_probe(struct platform_device *pdev)
 
 	init_waitqueue_head(&dsi->irq_wait_queue);
 
-	platform_set_drvdata(pdev, dsi);
-
 	dsi->bridge.of_node = dev->of_node;
 	dsi->bridge.type = DRM_MODE_CONNECTOR_DSI;
 
-- 
2.43.0

Claude review: drm/mediatek: dsi: Store driver data before invoking mipi_dsi_host_register

[Claude Code Review Bot]

Patch Review

The fix moves `platform_set_drvdata(pdev, dsi)` from after the IRQ request and waitqueue initialization to just before `mipi_dsi_host_register()`:

> +	platform_set_drvdata(pdev, dsi);
> +
>  	ret = mipi_dsi_host_register(&dsi->host);
>  	if (ret < 0)
>  		return dev_err_probe(dev, ret, "Failed to register DSI host\n");

This is correct. The call chain `mipi_dsi_host_register` -> `mtk_dsi_host_attach` -> `component_add` -> `mtk_dsi_bind` uses `dev_get_drvdata(dev)` to retrieve the `mtk_dsi` struct, so the drvdata must be set before registration.

The `dsi` pointer at this point in `mtk_dsi_probe` has already been allocated (via `devm_drm_bridge_alloc`), driver data matched, clocks obtained, registers mapped, PHY acquired, and the IRQ number retrieved — all the fields that `mtk_dsi_bind` might need are initialized. The `host.ops` and `host.dev` assignments are also already done on the lines immediately above.

If `mipi_dsi_host_register()` fails after drvdata is set, the drvdata will point to the `dsi` struct which is devres-managed and will be freed as part of device cleanup — this is harmless since the device itself won't proceed to use the stale drvdata after a failed probe.

No issues found. The fix is minimal, correct, and well-documented.

---
Generated by Claude Code Patch Reviewer

Claude review: drm/mediatek: dsi: Store driver data before invoking mipi_dsi_host_register

[Claude Code Review Bot]

Overall Series Review

Subject: drm/mediatek: dsi: Store driver data before invoking mipi_dsi_host_register
Author: Luca Leonardo Scorcia <l.scorcia@gmail.com>
Patches: 1
Reviewed: 2026-02-24T10:09:17.084197

---

This is a single-patch fix for a NULL pointer dereference during mediatek-drm DSI probe. The bug is straightforward: commit e4732b590a77 rearranged the probe sequence so that `mipi_dsi_host_register()` is called before `platform_set_drvdata()`, but `mipi_dsi_host_register()` can synchronously trigger `mtk_dsi_host_attach()` -> `component_add()` -> `mtk_dsi_bind()`, which calls `dev_get_drvdata()` and dereferences the result. Since drvdata is still NULL at that point, the kernel crashes.

The fix is minimal and correct: move `platform_set_drvdata(pdev, dsi)` before the `mipi_dsi_host_register()` call. The commit message is well-written, includes the full crash trace for reference, and has an appropriate Fixes tag.

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Generated by Claude Code Patch Reviewer