[PATCH v14 0/2] Add Lontium LT7911EXC eDP to MIPI DSI bridge

[PATCH v14 0/2] Add Lontium LT7911EXC eDP to MIPI DSI bridge

[syyang]

From: Sunyun Yang <syyang@lontium.com>

The LT7911EXC is an I2C-controlled bridge that receives eDP1.4
and output mipi dsi. This series introduces:

- A device tree binding YAML file describing the hardware
- A new DRM bridge driver implementing the basic functionality

Signed-off-by: Sunyun Yang<syyang@lontium.com>
---
Change in v14:
- dt-binding:
- drm/bridge:
 1. [High] AB-BA / self-deadlock between the bridge's ocm_lock and DRM modeset                             [sashiko-bot]
    locks during hotplug notification. - fixed
 2. [High] Freeing the panel bridge in lt7911exc_dsi_host_detach while it is still
    attached to the DRM bridge chain causes a Use-After-Free. - fixed
- Link to v13: https://lore.kernel.org/lkml/20260529094547.869919-1-syyang@lontium.com/

Change in v13:
- dt-binding:
- drm/bridge:
 1. [High] Dangling pointer created during MIPI DSI host detach if the downstream                           [sashiko-bot]
           device is a bridge rather than a panel. - fixed
 2. [High] Firmware upgrade CRC mismatch due to unpadded partial page writes.
           - hardware erases the entire flash area into a default state of 0xff. When doing
             a partial page short write，the total unwritten residual bytes on the physical
             flash sector inherently retain their 0xff state. Therefore, no modification is required.
 3. [High] Firmware upgrade workqueue accesses `bridge.dev` without ensuring the DRM device is alive,
           leading to a Use-After-Free. - fixed
 4. [High] Regmap page selector cache desynchronization after device reset causes firmware upgrade
           commands to be routed to the wrong register page. - fixed
- Link to v12: https://lore.kernel.org/lkml/20260525010545.9470-1-syyang@lontium.com/

Change in v12:
- dt-binding:
- drm/bridge:
 1. Move the cleanup work of drm_panel_bridge_remove() forward into lt7911exc_dsi_host_detach().                        [sashiko-bot]
 2. Do not hold any lock during lt7911exc_reset().
- Link to v11: https://lore.kernel.org/lkml/20260522015735.2833-1-syyang@lontium.com/

Change in v11:
- dt-binding:
- drm/bridge:
 1. Removed Reviewed-by, we would appreciate it if the maintainer could help review this.
 2. Use devm_gpiod_get(,, GPIOD_OUT_HIGH) to fix the reset GPIO backpowering issue.                                       [sashiko-bot]
 3. Fixed Use-After-Free vulnerability due to dynamic DRM bridge removal in DSI detach callback.
 4. Fixed Use-After-Free of regmap during DRM teardown because firmware upgrade worker defeats removal safeguard.
 5. Fixed firmware upgrade performs a hardware reset, causing silent loss of DRM state and a blank screen.
 6. Use of kmalloc for a 64KB software buffer is susceptible to memory fragmentation failures - Fix by using kvmalloc
 7. Use the 'lt7911exc->ocm_lock' mutex and the 'lt7911exc->upgrade' flag to resolve the race condition between
    DRM atomic modeset and firmware upgrade.
 8. Use the 'lt7911exc->upgrade_lock' mutex to prevent redundant upgrades.
 9. Use the 'lt7911exc->removed' flag to prevent the driver from being triggered to upgrade during the unload process.
- Link to v10: https://lore.kernel.org/lkml/20260519135816.26996-1-syyang@lontium.com/

Change in v10:
- dt-binding:
- drm/bridge:
 1. Fixed the firmware upgrade error paths to always clear the upgrade
    flag before returning, including firmware size validation failures
    and allocation failures.                                                                [sashiko-bot]
 2. Added proper locking in lt7911exc_atomic_pre_enable() and
    lt7911exc_atomic_post_disable() to serialize register accesses with the
    firmware upgrade flow and avoid concurrent I2C transactions.
 3. Added an exclusivity check in lt7911exc_dsi_host_attach() to reject multiple
    downstream attachments and prevent repeated drm_bridge_add() calls and panel bridge leaks.
 4. Reworked lt7911exc_firmware_store() to use mutex_trylock() so concurrent sysfs writers
    immediately return -EBUSY instead of blocking behind an active firmware upgrade.
 5. Updated the remove path to prevent new firmware upgrade work from being queued after
    device removal by setting the upgrade state before cancelling the worker.
- Link to v9: https://lore.kernel.org/lkml/20260519105019.22622-1-syyang@lontium.com/

Change in v9:
- dt-binding:
- drm/bridge:
 1. DSI transfer callback returns success for reads without populating                        [sashiko-bot]
    the receive buffer, leaking uninitialized memory. - fixed it by
    implementing  a strict whitelist mechanism.
 2. DSI transfer callback polls for eDP video readiness before the
    upstream encoder is enabled, guaranteeing a timeout. - removed
 3. The driver attempts I2C transfers while the hardware is held in
    physical reset. - fixed
 4. Missing DRM_MIPI_DSI Kconfig dependency causes linker errors. - fixed
 5. request_firmware is called while holding the hardware lock and
    halting the MCU, risking a system pipeline stall. - fixed
 6. Sleeping functions are called from atomic context in the DRM bridge callbacks. - fixed
 7. lt7911exc_dsi_host_transfer bypasses the required MCU hardware halt sequence. - fixed by
    internal firmware controls the panel initialization sequence and handles all MIPI
    DSI command transmission.
- Link to v8: https://lore.kernel.org/lkml/20260515080934.9870-1-syyang@lontium.com/

Change in v8:
- dt-binding:
- drm/bridge:
 1. Protect firmware upgrade and DRM bridge callback paths with ocm_lock.          [sashiko-bot]
 2. Remove the hardware reset from the remove callback, and ensure that
    all hardware reset operations are protected by ocm_lock.
 3. crc reconstruction explicitly casts each byte to u32 before shifting
 4. The display configuration is handled by the firmware, and the MIPI
    DSI host registration issue has been fixed.
 5. The batch register read/write operations have already been updated
    to include return value checking.
 6. The dev_err_probe() used outside of probe context has been fixed.
- Link to v7: https://lore.kernel.org/lkml/20260512064013.40066-1-syyang@lontium.com/

Change in v7:
- dt-binding:
 1. fix commit message typos(Receiver、signal)                            [sashiko-bot]
 2. remove the ambiguity caused by "signal/dual".
- drm/bridge:
 1. using devm_regulator_get_enable avoids power leaks.                   [sashiko-bot]
 2. set reset gpio is low after cutting off power in lt7911exc_remove function, avoid backpowering.
 3. synchronous request_firmware() call cause a permanent probe failure if the driver is built-in,
    probe executes before the root filesystem is mounted, which would cause this to fail with -ENOENT,
    we have removed this functionality. Use trigger to upgrade.
 4. add `depends on I2C` and `select REGMAP_I2C` in Kconfig.
 5. add return value of `devm_drm_bridge_add()` in `probe()`.
 6. add directly header files (linux/slab.h, linux/delay.h, linux/regulator/consumer.h)
- Link to v6: https://lore.kernel.org/lkml/20260508134702.4713-1-syyang@lontium.com/

Change in v6:
- dt-binding:
- drm/bridge:
 1. use #define FW_FILE  "Lontium/lt7911exc_fw.bin" to match linux-firmware
- Link to v5: https://lore.kernel.org/lkml/20260506013153.2240-1-syyang@lontium.com/

Change in v5:
- dt-binding:
- drm/bridge:
 1. Change "mipi" to "mipi dsi" in the commit message.     [Dmitry]
 2. Change "eDP/MIPI" to "eDP/MIPI DSI" in Kconfig.
- Link to v4: https://lore.kernel.org/lkml/20260430094612.3408174-1-syyang@lontium.com/

Change in v4:
- dt-binding:
 1. Fix the missing spaces on the "subject".             [Krzysztof]
 2. Fix the error descriptions for port@0 and port@1.
- drm/bridge:
- Link to v3: https://lore.kernel.org/lkml/20260429040541.3404116-1-syyang@lontium.com/

Change in v3:
- dt-binding:
- drm/bridge:
 1. already submit lt7911exc_fw.bin to linux-firmware.  [Dmitry]
 2. remove lt7911exc_remove function.
 3. drop  the "lontium, "  in lt7911exc_i2c_table.
- Link to v2: https://lore.kernel.org/lkml/20260428063224.3316655-1-syyang@lontium.com/

Change in v2:
- dt-binding:
 1. reset pins use active low.                        [Dmitry]
- drm/bridge:
 1. use atomic_* callbacks.                           [Quentin]
 2. fix the incorrect formatting and spaces.
 3. add the required header files.                    [Dmitry]
 4. remove "enabled" flag.
 5. remove *fw from the lt7911exc struct.
 6. .max_register and .range_max use actual range.
 7. regulator use bulk interface.
 8. use dev_err_probe, devm_mutex_init and devm_drm_bridge_add.
 9. Replace GPL v2 with GPL.
- Link to v1: https://lore.kernel.org/lkml/20260420023354.1192642-1-syyang@lontium.com/

---
Sunyun Yang (2):
  dt-bindings: bridge: Add Lontium LT7911EXC eDP to MIPI DSI bridge
  drm/bridge: Add Lontium LT7911EXC eDP to MIPI DSI bridge

 .../display/bridge/lontium,lt7911exc.yaml     |  89 ++
 drivers/gpu/drm/bridge/Kconfig                |  16 +
 drivers/gpu/drm/bridge/Makefile               |   1 +
 drivers/gpu/drm/bridge/lontium-lt7911exc.c    | 810 ++++++++++++++++++
 4 files changed, 916 insertions(+)
 create mode 100644 Documentation/devicetree/bindings/display/bridge/lontium,lt7911exc.yaml
 create mode 100644 drivers/gpu/drm/bridge/lontium-lt7911exc.c

-- 
2.34.1

[PATCH v14 2/2] drm/bridge: Add Lontium LT7911EXC eDP to MIPI DSI bridge

[syyang]

From: Sunyun Yang <syyang@lontium.com>

Add support for the Lontium LT7911EXC bridge chip, which converts
eDP input to MIPI DSI output using an internal firmware-controlled
pipeline.

The driver provides:
- DRM bridge integration for eDP-to-DSI routing
- MIPI DSI host interface for downstream panel attachment
- Firmware upgrade mechanism over I2C (erase/program/verify)
- GPIO-based reset and regulator management

Display timing and MIPI DCS packet generation are handled by the chip
firmware and are not configured by the driver.

Signed-off-by: Sunyun Yang <syyang@lontium.com>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@oss.qualcomm.com>
---
 drivers/gpu/drm/bridge/Kconfig             |  16 +
 drivers/gpu/drm/bridge/Makefile            |   1 +
 drivers/gpu/drm/bridge/lontium-lt7911exc.c | 810 +++++++++++++++++++++
 3 files changed, 827 insertions(+)
 create mode 100644 drivers/gpu/drm/bridge/lontium-lt7911exc.c

diff --git a/drivers/gpu/drm/bridge/Kconfig b/drivers/gpu/drm/bridge/Kconfig
index c3209b0f4678..013e431e8871 100644
--- a/drivers/gpu/drm/bridge/Kconfig
+++ b/drivers/gpu/drm/bridge/Kconfig
@@ -132,6 +132,22 @@ config DRM_ITE_IT6505
 	help
 	  ITE IT6505 DisplayPort bridge chip driver.
 
+config DRM_LONTIUM_LT7911EXC
+	tristate "Lontium eDP/MIPI DSI bridge"
+	depends on OF
+	depends on I2C
+	select CRC32
+	select DRM_PANEL
+	select DRM_MIPI_DSI
+	select DRM_KMS_HELPER
+	select FW_LOADER
+	select REGMAP_I2C
+	help
+	  DRM driver for the Lontium LT7911EXC bridge
+	  chip.The LT7911EXC converts eDP input to MIPI
+	  DSI output.
+	  Please say Y if you have such hardware.
+
 config DRM_LONTIUM_LT8912B
 	tristate "Lontium LT8912B DSI/HDMI bridge"
 	depends on OF
diff --git a/drivers/gpu/drm/bridge/Makefile b/drivers/gpu/drm/bridge/Makefile
index beab5b695a6e..70ddca75dd3a 100644
--- a/drivers/gpu/drm/bridge/Makefile
+++ b/drivers/gpu/drm/bridge/Makefile
@@ -13,6 +13,7 @@ obj-$(CONFIG_DRM_I2C_NXP_TDA998X) += tda998x.o
 obj-$(CONFIG_DRM_INNO_HDMI) += inno-hdmi.o
 obj-$(CONFIG_DRM_ITE_IT6263) += ite-it6263.o
 obj-$(CONFIG_DRM_ITE_IT6505) += ite-it6505.o
+obj-$(CONFIG_DRM_LONTIUM_LT7911EXC) += lontium-lt7911exc.o
 obj-$(CONFIG_DRM_LONTIUM_LT8912B) += lontium-lt8912b.o
 obj-$(CONFIG_DRM_LONTIUM_LT9211) += lontium-lt9211.o
 obj-$(CONFIG_DRM_LONTIUM_LT9611) += lontium-lt9611.o
diff --git a/drivers/gpu/drm/bridge/lontium-lt7911exc.c b/drivers/gpu/drm/bridge/lontium-lt7911exc.c
new file mode 100644
index 000000000000..f7cd89bcc811
--- /dev/null
+++ b/drivers/gpu/drm/bridge/lontium-lt7911exc.c
@@ -0,0 +1,810 @@
+// SPDX-License-Identifier: GPL-2.0
+/*
+ * Copyright (C) 2026 Lontium Semiconductor, Inc.
+ */
+
+#include <linux/crc32.h>
+#include <linux/delay.h>
+#include <linux/firmware.h>
+#include <linux/gpio/consumer.h>
+#include <linux/i2c.h>
+#include <linux/module.h>
+#include <linux/mutex.h>
+#include <linux/of_graph.h>
+#include <linux/platform_device.h>
+#include <linux/regmap.h>
+#include <linux/regulator/consumer.h>
+#include <linux/slab.h>
+
+#include <drm/drm_atomic_helper.h>
+#include <drm/drm_bridge.h>
+#include <drm/drm_mipi_dsi.h>
+#include <drm/drm_of.h>
+#include <drm/drm_probe_helper.h>
+#include <video/mipi_display.h>
+
+#define FW_SIZE (64 * 1024)
+#define LT_PAGE_SIZE 32
+#define FW_FILE  "Lontium/lt7911exc_fw.bin"
+#define LT7911EXC_PAGE_CONTROL 0xff
+
+struct lt7911exc_dsi_output {
+	struct mipi_dsi_device *dev;
+	struct drm_panel *panel;
+	struct drm_bridge *bridge;
+};
+
+struct lt7911exc {
+	struct device *dev;
+	struct i2c_client *client;
+	struct drm_bridge bridge;
+	struct work_struct work;
+	struct mipi_dsi_host dsi_host;
+	struct lt7911exc_dsi_output output;
+	struct regmap *regmap;
+	/* Fast lock: guards short register r/w and status checks */
+	struct mutex ocm_lock;
+	/* Long lock: serializes firmware upgrade process to prevent DRM interference */
+	struct mutex upgrade_lock;
+	struct gpio_desc *reset_gpio;
+	int fw_version;
+	bool upgrade;
+	bool removed;
+};
+
+static const struct regmap_config lt7911exc_regmap_config = {
+	.reg_bits = 8,
+	.val_bits = 8,
+	.max_register = 0xff,
+};
+
+static u32 cal_crc32_custom(const u8 *data, u64 length)
+{
+	u32 crc = 0xffffffff;
+	u8 buf[4];
+	u64 i;
+
+	if (!length || (length & 3))
+		return 0;
+
+	for (i = 0; i < length; i += 4) {
+		buf[0] = data[i + 3];
+		buf[1] = data[i + 2];
+		buf[2] = data[i + 1];
+		buf[3] = data[i + 0];
+		crc = crc32_be(crc, buf, 4);
+	}
+
+	return crc;
+}
+
+static inline struct lt7911exc *bridge_to_lt7911exc(struct drm_bridge *bridge)
+{
+	return container_of(bridge, struct lt7911exc, bridge);
+}
+
+static inline struct lt7911exc *dsi_host_to_lt7911exc(struct mipi_dsi_host *host)
+{
+	return container_of(host, struct lt7911exc, dsi_host);
+}
+
+static void lt7911exc_reset(struct lt7911exc *lt7911exc)
+{
+	/* Assert reset pin: logical 1 -> physical state low (Reset Active) */
+	gpiod_set_value_cansleep(lt7911exc->reset_gpio, 1);
+	msleep(20);
+
+	/* Deassert reset pin: logical 0 -> physical state high (Run state) */
+	gpiod_set_value_cansleep(lt7911exc->reset_gpio, 0);
+	msleep(400);
+
+	dev_dbg(lt7911exc->dev, "lt7911exc physical hardware reset sequence completed.\n");
+}
+
+static int lt7911exc_hw_mcu_halt(struct lt7911exc *lt7911exc)
+{
+	struct device *dev = lt7911exc->dev;
+	int ret;
+
+	ret = regmap_write(lt7911exc->regmap, LT7911EXC_PAGE_CONTROL, 0xe0);
+	if (ret) {
+		dev_err(dev, "Failed to switch to page 0xe0\n");
+		return ret;
+	}
+
+	return regmap_write(lt7911exc->regmap, 0xee, 0x01);
+}
+
+static int lt7911exc_hw_mcu_run(struct lt7911exc *lt7911exc)
+{
+	struct device *dev = lt7911exc->dev;
+	int ret;
+
+	ret = regmap_write(lt7911exc->regmap, LT7911EXC_PAGE_CONTROL, 0xe0);
+	if (ret) {
+		dev_err(dev, "Failed to switch to page 0xe0\n");
+		return ret;
+	}
+
+	return regmap_write(lt7911exc->regmap, 0xee, 0x00);
+}
+
+static int lt7911exc_regulator_enable(struct lt7911exc *lt7911exc)
+{
+	int ret;
+
+	ret = devm_regulator_get_enable(lt7911exc->dev, "vcc");
+	if (ret < 0)
+		return dev_err_probe(lt7911exc->dev, ret, "failed to enable vcc regulator\n");
+
+	usleep_range(5000, 10000);
+
+	ret = devm_regulator_get_enable(lt7911exc->dev, "vdd");
+	if (ret < 0)
+		return dev_err_probe(lt7911exc->dev, ret, "failed to enable vdd regulator\n");
+
+	return 0;
+}
+
+static int lt7911exc_read_version(struct lt7911exc *lt7911exc)
+{
+	struct device *dev = lt7911exc->dev;
+	u8 buf[3];
+	int ret;
+
+	ret = regmap_write(lt7911exc->regmap, LT7911EXC_PAGE_CONTROL, 0xe0);
+	if (ret) {
+		dev_err(dev, "Failed to switch to page 0xe0\n");
+		return ret;
+	}
+
+	/* no need to halt MCU for this register access */
+	ret = regmap_bulk_read(lt7911exc->regmap, 0x81, buf, ARRAY_SIZE(buf));
+	if (ret)
+		return ret;
+
+	return (buf[0] << 16) | (buf[1] << 8) | buf[2];
+}
+
+/* after erasure, the data in the flash is all 0xff */
+static int lt7911exc_block_erase(struct lt7911exc *lt7911exc)
+{
+	struct device *dev = lt7911exc->dev;
+	const u32 addr = 0x00;
+	int ret;
+
+	ret = regmap_write(lt7911exc->regmap, LT7911EXC_PAGE_CONTROL, 0xe0);
+	if (ret) {
+		dev_err(dev, "Failed to switch to page 0xe0\n");
+		return ret;
+	}
+	ret = regmap_write(lt7911exc->regmap, 0xee, 0x01);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x54, 0x01);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x55, 0x06);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x51, 0x01);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x51, 0x00);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x54, 0x05);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x55, 0xd8);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x5a, (addr >> 16) & 0xff);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x5b, (addr >> 8) & 0xff);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x5c, addr & 0xff);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x51, 0x01);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x50, 0x00);
+	if (ret)
+		return ret;
+
+	msleep(200);
+	dev_dbg(dev, "erase flash done.\n");
+
+	return 0;
+}
+
+static int lt7911exc_prog_init(struct lt7911exc *lt7911exc, u64 addr)
+{
+	struct device *dev = lt7911exc->dev;
+	int ret;
+
+	ret = regmap_write(lt7911exc->regmap, LT7911EXC_PAGE_CONTROL, 0xe0);
+	if (ret) {
+		dev_err(dev, "Failed to switch to page 0xe0 in prog_init: %d\n", ret);
+		return ret;
+	}
+	ret = regmap_write(lt7911exc->regmap, 0xee, 0x01);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x5f, 0x01);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x5a, (addr >> 16) & 0xff);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x5b, (addr >> 8) & 0xff);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x5c, addr & 0xff);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+/*
+ * Hardware Flash Erase Behavior Note:
+ * The LT7911EXC hardware erases the entire flash area into a default state of 0xff.
+ * When doing a partial page short write (where fw->size is not aligned to a 32-byte
+ * page boundary), the total unwritten residual bytes on the physical flash sector inherently
+ * retain their 0xff state.
+ * Therefore, raw physical short-write transmission is perfectly clean and matches the 0xff padded
+ * software calculated CRC32. No software-side buffer padding is required.
+ */
+static int lt7911exc_write_data(struct lt7911exc *lt7911exc, const struct firmware *fw, u64 addr)
+{
+	struct device *dev = lt7911exc->dev;
+	int ret;
+	int page = 0, num = 0, page_len = 0;
+	u64 size, offset;
+	const u8 *data;
+
+	data = fw->data;
+	size = fw->size;
+	page = (size + LT_PAGE_SIZE - 1) / LT_PAGE_SIZE;
+	if (page * LT_PAGE_SIZE > FW_SIZE) {
+		dev_err(dev, "firmware size out of range\n");
+		return -EINVAL;
+	}
+
+	for (num = 0; num < page; num++) {
+		offset = num * LT_PAGE_SIZE;
+		page_len = (offset + LT_PAGE_SIZE <= size) ? LT_PAGE_SIZE : (size - offset);
+		ret = lt7911exc_prog_init(lt7911exc, addr);
+		if (ret)
+			return ret;
+
+		ret = regmap_raw_write(lt7911exc->regmap, 0x5d, &data[offset], page_len);
+		if (ret) {
+			dev_err(dev, "write error at page %d\n", num);
+			return ret;
+		}
+
+		//write method for less than LT_PAGE_SIZE bytes.
+		if (page_len < LT_PAGE_SIZE) {
+			regmap_write(lt7911exc->regmap, 0x5f, 0x05);
+			regmap_write(lt7911exc->regmap, 0x5f, 0x01);
+			//hardware requires delay
+			usleep_range(1000, 2000);
+		}
+
+		regmap_write(lt7911exc->regmap, 0x5f, 0x00);
+		addr += LT_PAGE_SIZE;
+	}
+
+	return 0;
+}
+
+static int lt7911exc_write_crc(struct lt7911exc *lt7911exc, u32 crc32, u64 addr)
+{
+	u8 crc[4];
+	int ret;
+
+	crc[0] = crc32 & 0xff;
+	crc[1] = (crc32 >> 8) & 0xff;
+	crc[2] = (crc32 >> 16) & 0xff;
+	crc[3] = (crc32 >> 24) & 0xff;
+
+	ret = regmap_write(lt7911exc->regmap, 0x5f, 0x01);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x5a, (addr >> 16) & 0xff);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x5b, (addr >> 8) & 0xff);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x5c, addr & 0xff);
+	if (ret)
+		return ret;
+
+	ret = regmap_raw_write(lt7911exc->regmap, 0x5d, crc, 4);
+	if (ret)
+		return ret;
+
+	ret = regmap_write(lt7911exc->regmap, 0x5f, 0x05);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x5f, 0x01);
+	if (ret)
+		return ret;
+
+	usleep_range(1000, 2000);
+
+	ret = regmap_write(lt7911exc->regmap, 0x5f, 0x00);
+	if (ret)
+		return ret;
+
+	return 0;
+}
+
+static int lt7911exc_upgrade_result(struct lt7911exc *lt7911exc, u32 crc32)
+{
+	struct device *dev = lt7911exc->dev;
+	u32 read_hw_crc = 0;
+	u8 crc_tmp[4];
+	int ret;
+
+	ret = regmap_write(lt7911exc->regmap, LT7911EXC_PAGE_CONTROL, 0xe0);
+	if (ret) {
+		dev_err(dev, "Failed to switch to page 0xe0 in prog_init: %d\n", ret);
+		return ret;
+	}
+	ret = regmap_write(lt7911exc->regmap, 0xee, 0x01);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x7b, 0x60);
+	if (ret)
+		return ret;
+	ret = regmap_write(lt7911exc->regmap, 0x7b, 0x40);
+	if (ret)
+		return ret;
+
+	msleep(150);
+
+	ret = regmap_bulk_read(lt7911exc->regmap, 0x22, crc_tmp, ARRAY_SIZE(crc_tmp));
+	if (ret) {
+		dev_err(lt7911exc->dev, "Failed to read CRC: %d\n", ret);
+		return ret;
+	}
+
+	ret = regmap_write(lt7911exc->regmap, 0xee, 0x00);
+	if (ret)
+		return ret;
+
+	read_hw_crc = ((u32)crc_tmp[0] << 24) | ((u32)crc_tmp[1] << 16) |
+				((u32)crc_tmp[2] << 8) | ((u32)crc_tmp[3]);
+
+	if (read_hw_crc != crc32) {
+		dev_err(dev, "lt7911exc firmware upgrade failed, expected CRC=0x%08x, read CRC=0x%08x\n",
+			crc32, read_hw_crc);
+		return -EIO;
+	}
+
+	dev_dbg(dev, "lt7911exc firmware upgrade success, CRC=0x%08x\n", read_hw_crc);
+	return 0;
+}
+
+static void lt7911exc_firmware_upgrade_work(struct work_struct *work)
+{
+	struct lt7911exc *lt7911exc = container_of(work, struct lt7911exc, work);
+	struct device *dev = lt7911exc->dev;
+	const struct firmware *fw;
+	struct drm_device *drm_dev = NULL;
+	u8 *buffer;
+	size_t total_size = FW_SIZE - 4;
+	u32 crc32;
+	int ret;
+
+	mutex_lock(&lt7911exc->upgrade_lock);
+	if (lt7911exc->removed) {
+		mutex_unlock(&lt7911exc->upgrade_lock);
+		return;
+	}
+
+	ret = request_firmware(&fw, FW_FILE, dev);
+	if (ret) {
+		dev_err(dev, "failed to load '%s'\n", FW_FILE);
+		goto out_clear_status;
+	}
+
+	if (fw->size > total_size) {
+		dev_err(dev, "firmware too large (%zu > %zu)\n", fw->size, total_size);
+		goto out_release_fw;
+	}
+
+	buffer = kvmalloc(total_size, GFP_KERNEL);
+	if (!buffer) {
+		ret = -ENOMEM;
+		goto out_release_fw;
+	}
+
+	memset(buffer, 0xff, total_size);
+	memcpy(buffer, fw->data, fw->size);
+	crc32 = cal_crc32_custom(buffer, total_size);
+
+	kvfree(buffer);
+
+	lt7911exc_reset(lt7911exc);
+
+	mutex_lock(&lt7911exc->ocm_lock);
+	lt7911exc_hw_mcu_halt(lt7911exc);
+	mutex_unlock(&lt7911exc->ocm_lock);
+
+	ret = lt7911exc_block_erase(lt7911exc);
+	if (ret) {
+		dev_err(dev, "failed to block erase.\n");
+		goto out_release_fw;
+	}
+
+	ret = lt7911exc_write_data(lt7911exc, fw, 0);
+	if (ret < 0) {
+		dev_err(dev, "failed to write firmware data\n");
+		goto out_release_fw;
+	}
+
+	ret = lt7911exc_write_crc(lt7911exc, crc32, FW_SIZE - 4);
+	if (ret < 0) {
+		dev_err(dev, "failed to write firmware crc\n");
+		goto out_release_fw;
+	}
+
+	lt7911exc_reset(lt7911exc);
+
+	ret = lt7911exc_upgrade_result(lt7911exc, crc32);
+	if (ret)
+		dev_err(dev, "firmware verification failed\n");
+
+	mutex_lock(&lt7911exc->ocm_lock);
+	lt7911exc_hw_mcu_run(lt7911exc);
+	lt7911exc->fw_version = lt7911exc_read_version(lt7911exc);
+	if (lt7911exc->bridge.dev)
+		drm_dev = lt7911exc->bridge.dev;
+
+	mutex_unlock(&lt7911exc->ocm_lock);
+
+	/* Notify DRM framework that hardware state changed/needs a modeset */
+	if (drm_dev)
+		drm_kms_helper_hotplug_event(drm_dev);
+
+out_release_fw:
+	release_firmware(fw);
+
+out_clear_status:
+	/* Only clear status if the module is not in the process of remove */
+	mutex_lock(&lt7911exc->ocm_lock);
+	if (!lt7911exc->removed)
+		lt7911exc->upgrade = false;
+	mutex_unlock(&lt7911exc->ocm_lock);
+
+	mutex_unlock(&lt7911exc->upgrade_lock);
+}
+
+static void lt7911exc_atomic_pre_enable(struct drm_bridge *bridge, struct drm_atomic_state *state)
+{
+	struct lt7911exc *lt7911exc = bridge_to_lt7911exc(bridge);
+
+	guard(mutex)(&lt7911exc->ocm_lock);
+
+	//enable mipi stream
+	if (!lt7911exc->upgrade) {
+		regmap_write(lt7911exc->regmap, LT7911EXC_PAGE_CONTROL, 0xe0);
+		regmap_write(lt7911exc->regmap, 0xb0, 0x01);
+	}
+}
+
+static void lt7911exc_atomic_post_disable(struct drm_bridge *bridge, struct drm_atomic_state *state)
+{
+	struct lt7911exc *lt7911exc = bridge_to_lt7911exc(bridge);
+
+	guard(mutex)(&lt7911exc->ocm_lock);
+
+	//disable mipi stream
+	if (!lt7911exc->upgrade) {
+		regmap_write(lt7911exc->regmap, LT7911EXC_PAGE_CONTROL, 0xe0);
+		regmap_write(lt7911exc->regmap, 0xb0, 0x00);
+	}
+}
+
+static int lt7911exc_bridge_attach(struct drm_bridge *bridge,
+				   struct drm_encoder *encoder,
+				   enum drm_bridge_attach_flags flags)
+{
+	struct lt7911exc *lt7911exc = bridge_to_lt7911exc(bridge);
+
+	if (!lt7911exc->output.bridge) {
+		dev_warn(lt7911exc->dev, "Next bridge/panel not attached yet, deferring\n");
+		return -EPROBE_DEFER;
+	}
+
+	return drm_bridge_attach(encoder, lt7911exc->output.bridge, bridge, flags);
+}
+
+static void lt7911exc_bridge_detach(struct drm_bridge *bridge)
+{
+	struct lt7911exc *lt7911exc = bridge_to_lt7911exc(bridge);
+
+	guard(mutex)(&lt7911exc->ocm_lock);
+	bridge->dev = NULL;
+}
+
+static const struct drm_bridge_funcs lt7911exc_bridge_funcs = {
+	.attach = lt7911exc_bridge_attach,
+	.detach = lt7911exc_bridge_detach,
+	.atomic_pre_enable = lt7911exc_atomic_pre_enable,
+	.atomic_post_disable = lt7911exc_atomic_post_disable,
+	.atomic_reset = drm_atomic_helper_bridge_reset,
+	.atomic_duplicate_state = drm_atomic_helper_bridge_duplicate_state,
+	.atomic_destroy_state = drm_atomic_helper_bridge_destroy_state,
+};
+
+static int lt7911exc_dsi_host_attach(struct mipi_dsi_host *host, struct mipi_dsi_device *dev)
+{
+	struct lt7911exc *lt7911exc = dsi_host_to_lt7911exc(host);
+	struct drm_bridge *bridge;
+	struct drm_panel *panel;
+	int ret;
+
+	if (lt7911exc->output.dev)
+		return -EBUSY;
+
+	ret = drm_of_find_panel_or_bridge(host->dev->of_node, 1, 0, &panel, &bridge);
+	if (ret)
+		return ret;
+
+	if (panel) {
+		bridge = devm_drm_panel_bridge_add_typed(lt7911exc->dev, panel,
+							 DRM_MODE_CONNECTOR_DSI);
+		if (IS_ERR(bridge))
+			return PTR_ERR(bridge);
+	}
+	lt7911exc->output.dev = dev;
+	lt7911exc->output.bridge = bridge;
+	lt7911exc->output.panel = panel;
+
+	return 0;
+}
+
+static int lt7911exc_dsi_host_detach(struct mipi_dsi_host *host, struct mipi_dsi_device *dev)
+{
+	struct lt7911exc *lt7911exc = dsi_host_to_lt7911exc(host);
+
+	if (!lt7911exc->output.dev)
+		return 0;
+
+	lt7911exc->output.bridge = NULL;
+	lt7911exc->output.panel = NULL;
+	lt7911exc->output.dev = NULL;
+
+	return 0;
+}
+
+/*
+ * The internal firmware controls the panel initialization
+ * sequence and handles all MIPI DSI command transmission.
+ */
+static ssize_t lt7911exc_dsi_host_transfer(struct mipi_dsi_host *host,
+					   const struct mipi_dsi_msg *msg)
+{
+	struct lt7911exc *lt7911exc = dsi_host_to_lt7911exc(host);
+
+	if (msg->rx_len) {
+		dev_warn(lt7911exc->dev, "MIPI DSI read is not supported\n");
+		return -EOPNOTSUPP;
+	}
+
+	switch (msg->type) {
+	case MIPI_DSI_DCS_SHORT_WRITE:
+	case MIPI_DSI_DCS_SHORT_WRITE_PARAM:
+	case MIPI_DSI_DCS_LONG_WRITE:
+	case MIPI_DSI_GENERIC_SHORT_WRITE_0_PARAM:
+	case MIPI_DSI_GENERIC_SHORT_WRITE_1_PARAM:
+	case MIPI_DSI_GENERIC_SHORT_WRITE_2_PARAM:
+	case MIPI_DSI_GENERIC_LONG_WRITE:
+	break;
+	default:
+	return -EOPNOTSUPP;
+	}
+
+	guard(mutex)(&lt7911exc->ocm_lock);
+
+	if (lt7911exc->upgrade)
+		return -EBUSY;
+
+	return msg->tx_len;
+}
+
+static const struct mipi_dsi_host_ops lt7911exc_dsi_host_ops = {
+	.attach = lt7911exc_dsi_host_attach,
+	.detach = lt7911exc_dsi_host_detach,
+	.transfer = lt7911exc_dsi_host_transfer,
+};
+
+static ssize_t lt7911exc_firmware_store(struct device *dev, struct device_attribute *attr,
+					const char *buf, size_t len)
+{
+	struct lt7911exc *lt7911exc = dev_get_drvdata(dev);
+
+	if (!lt7911exc)
+		return -ENODEV;
+
+	if (!mutex_trylock(&lt7911exc->upgrade_lock))
+		return -EBUSY;
+
+	mutex_lock(&lt7911exc->ocm_lock);
+
+	if (lt7911exc->upgrade || lt7911exc->removed) {
+		mutex_unlock(&lt7911exc->ocm_lock);
+		mutex_unlock(&lt7911exc->upgrade_lock);
+		return -EBUSY;
+	}
+
+	lt7911exc->upgrade = true;
+	mutex_unlock(&lt7911exc->ocm_lock);
+	mutex_unlock(&lt7911exc->upgrade_lock);
+
+	schedule_work(&lt7911exc->work);
+
+	return len;
+}
+
+static ssize_t lt7911exc_firmware_show(struct device *dev, struct device_attribute *attr, char *buf)
+{
+	struct lt7911exc *lt7911exc = dev_get_drvdata(dev);
+	int version;
+
+	if (!lt7911exc)
+		return -ENODEV;
+
+	mutex_lock(&lt7911exc->ocm_lock);
+	version = lt7911exc->fw_version;
+	mutex_unlock(&lt7911exc->ocm_lock);
+	return sysfs_emit(buf, "0x%04x\n", version);
+}
+
+static DEVICE_ATTR_RW(lt7911exc_firmware);
+
+static struct attribute *lt7911exc_attrs[] = {
+	&dev_attr_lt7911exc_firmware.attr,
+	NULL,
+};
+
+static const struct attribute_group lt7911exc_attr_group = {
+	.attrs = lt7911exc_attrs,
+};
+
+static const struct attribute_group *lt7911exc_attr_groups[] = {
+	&lt7911exc_attr_group,
+	NULL,
+};
+
+static int lt7911exc_probe(struct i2c_client *client)
+{
+	struct lt7911exc *lt7911exc;
+	struct device *dev = &client->dev;
+	struct device_node *np = dev->of_node;
+	int ret;
+
+	if (!np)
+		return -ENODEV;
+
+	if (!i2c_check_functionality(client->adapter, I2C_FUNC_I2C))
+		return dev_err_probe(dev, -ENODEV, "device doesn't support I2C\n");
+
+	lt7911exc = devm_drm_bridge_alloc(dev, struct lt7911exc, bridge, &lt7911exc_bridge_funcs);
+	if (IS_ERR(lt7911exc))
+		return dev_err_probe(dev, PTR_ERR(lt7911exc), "drm bridge alloc failed.\n");
+
+	dev_set_drvdata(dev, lt7911exc);
+
+	lt7911exc->client = client;
+	lt7911exc->dev = dev;
+	lt7911exc->upgrade = false;
+	lt7911exc->removed = false;
+
+	ret = devm_mutex_init(dev, &lt7911exc->ocm_lock);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to init mutex\n");
+
+	ret = devm_mutex_init(dev, &lt7911exc->upgrade_lock);
+	if (ret)
+		return dev_err_probe(dev, ret, "failed to init upgrade_lock\n");
+
+	lt7911exc->regmap = devm_regmap_init_i2c(client, &lt7911exc_regmap_config);
+	if (IS_ERR(lt7911exc->regmap))
+		return dev_err_probe(dev, PTR_ERR(lt7911exc->regmap), "regmap i2c init failed\n");
+
+	lt7911exc->reset_gpio = devm_gpiod_get(dev, "reset", GPIOD_OUT_HIGH);
+	if (IS_ERR(lt7911exc->reset_gpio))
+		return dev_err_probe(dev, PTR_ERR(lt7911exc->reset_gpio),
+				     "failed to acquire reset gpio\n");
+
+	ret = lt7911exc_regulator_enable(lt7911exc);
+	if (ret)
+		return ret;
+
+	lt7911exc_reset(lt7911exc);
+
+	mutex_lock(&lt7911exc->ocm_lock);
+	lt7911exc->fw_version = lt7911exc_read_version(lt7911exc);
+	mutex_unlock(&lt7911exc->ocm_lock);
+
+	if (lt7911exc->fw_version < 0)
+		return dev_err_probe(dev, lt7911exc->fw_version, "failed read version of chip\n");
+
+	lt7911exc->dsi_host.dev = dev;
+	lt7911exc->dsi_host.ops = &lt7911exc_dsi_host_ops;
+	lt7911exc->bridge.of_node = np;
+
+	INIT_WORK(&lt7911exc->work, lt7911exc_firmware_upgrade_work);
+
+	i2c_set_clientdata(client, lt7911exc);
+
+	drm_bridge_add(&lt7911exc->bridge);
+
+	ret = mipi_dsi_host_register(&lt7911exc->dsi_host);
+	if (ret) {
+		drm_bridge_remove(&lt7911exc->bridge);
+		return ret;
+	}
+
+	return 0;
+}
+
+static void lt7911exc_remove(struct i2c_client *client)
+{
+	struct lt7911exc *lt7911exc = i2c_get_clientdata(client);
+
+	if (!lt7911exc)
+		return;
+
+	mutex_lock(&lt7911exc->ocm_lock);
+	lt7911exc->removed = true;
+	lt7911exc->upgrade = true;
+	mutex_unlock(&lt7911exc->ocm_lock);
+
+	cancel_work_sync(&lt7911exc->work);
+
+	mipi_dsi_host_unregister(&lt7911exc->dsi_host);
+	drm_bridge_remove(&lt7911exc->bridge);
+
+	gpiod_set_value_cansleep(lt7911exc->reset_gpio, 1);
+}
+
+static const struct i2c_device_id lt7911exc_i2c_table[] = {
+	{"lt7911exc"},
+	{/* sentinel */}
+};
+
+MODULE_DEVICE_TABLE(i2c, lt7911exc_i2c_table);
+
+static const struct of_device_id lt7911exc_devices[] = {
+	{.compatible = "lontium,lt7911exc"},
+	{/* sentinel */}
+};
+MODULE_DEVICE_TABLE(of, lt7911exc_devices);
+
+static struct i2c_driver lt7911exc_driver = {
+	.id_table	= lt7911exc_i2c_table,
+	.probe		= lt7911exc_probe,
+	.remove		= lt7911exc_remove,
+	.driver		= {
+		.name	= "lt7911exc",
+		.of_match_table = lt7911exc_devices,
+		.dev_groups = lt7911exc_attr_groups,
+	},
+};
+module_i2c_driver(lt7911exc_driver);
+
+MODULE_AUTHOR("SunYun Yang <syyang@lontium.com>");
+MODULE_DESCRIPTION("Lontium LT7911EXC EDP to MIPI DSI bridge driver");
+MODULE_LICENSE("GPL");
+MODULE_FIRMWARE(FW_FILE);
-- 
2.34.1

Re: [PATCH v14 2/2] drm/bridge: Add Lontium LT7911EXC eDP to MIPI DSI bridge

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 3 potential issue(s) to consider:
- [High] Using devm_drm_panel_bridge_add_typed() in the DSI host attach callback leaks memory and leaves dangling pointers when the downstream panel unbinds.
- [High] Potential use-after-free of the drm_device pointer in the firmware upgrade worker when the DRM display driver is unloaded.
- [High] Using stack buffers for I2C regmap bulk reads violates DMA mapping rules and can cause memory corruption.
--

commit a175e14df601fd080297e05f4671c7c7284dc3f0
Author: Sunyun Yang <syyang@lontium.com>

drm/bridge: Add Lontium LT7911EXC eDP to MIPI DSI bridge

Add support for the Lontium LT7911EXC bridge chip, which converts
eDP input to MIPI DSI output using an internal firmware-controlled
pipeline.

> diff --git a/drivers/gpu/drm/bridge/lontium-lt7911exc.c b/drivers/gpu/drm/bridge/lontium-lt7911exc.c
> new file mode 100644
> index 0000000000000..f7cd89bcc8119
> --- /dev/null
> +++ b/drivers/gpu/drm/bridge/lontium-lt7911exc.c
[ ... ]
> +static int lt7911exc_read_version(struct lt7911exc *lt7911exc)
> +{
> +	struct device *dev = lt7911exc->dev;
> +	u8 buf[3];
> +	int ret;
> +
> +	ret = regmap_write(lt7911exc->regmap, LT7911EXC_PAGE_CONTROL, 0xe0);
> +	if (ret) {
> +		dev_err(dev, "Failed to switch to page 0xe0\n");
> +		return ret;
> +	}
> +
> +	/* no need to halt MCU for this register access */
> +	ret = regmap_bulk_read(lt7911exc->regmap, 0x81, buf, ARRAY_SIZE(buf));

[Severity: High]
Can using a stack buffer for I2C regmap bulk reads cause memory corruption?

If the underlying I2C adapter uses DMA, the DMA API will attempt to map this
stack memory. The kernel forbids doing DMA on stack variables as it can share
cache lines with other data, resulting in memory corruption.

Should buf be dynamically allocated?

[ ... ]
> +static int lt7911exc_upgrade_result(struct lt7911exc *lt7911exc, u32 crc32)
> +{
> +	struct device *dev = lt7911exc->dev;
> +	u32 read_hw_crc = 0;
> +	u8 crc_tmp[4];
> +	int ret;
> +
> +	ret = regmap_write(lt7911exc->regmap, LT7911EXC_PAGE_CONTROL, 0xe0);
> +	if (ret) {
> +		dev_err(dev, "Failed to switch to page 0xe0 in prog_init: %d\n", ret);
> +		return ret;
> +	}
> +	ret = regmap_write(lt7911exc->regmap, 0xee, 0x01);
> +	if (ret)
> +		return ret;
> +	ret = regmap_write(lt7911exc->regmap, 0x7b, 0x60);
> +	if (ret)
> +		return ret;
> +	ret = regmap_write(lt7911exc->regmap, 0x7b, 0x40);
> +	if (ret)
> +		return ret;
> +
> +	msleep(150);
> +
> +	ret = regmap_bulk_read(lt7911exc->regmap, 0x22, crc_tmp, ARRAY_SIZE(crc_tmp));

[Severity: High]
Can this stack buffer also cause memory corruption if the I2C adapter uses DMA?
It looks like crc_tmp should be dynamically allocated as well.

[ ... ]
> +static void lt7911exc_firmware_upgrade_work(struct work_struct *work)
> +{
> +	struct lt7911exc *lt7911exc = container_of(work, struct lt7911exc, work);
> +	struct device *dev = lt7911exc->dev;
> +	const struct firmware *fw;
> +	struct drm_device *drm_dev = NULL;
[ ... ]
> +	mutex_lock(&lt7911exc->ocm_lock);
> +	lt7911exc_hw_mcu_run(lt7911exc);
> +	lt7911exc->fw_version = lt7911exc_read_version(lt7911exc);
> +	if (lt7911exc->bridge.dev)
> +		drm_dev = lt7911exc->bridge.dev;
> +
> +	mutex_unlock(&lt7911exc->ocm_lock);
> +
> +	/* Notify DRM framework that hardware state changed/needs a modeset */
> +	if (drm_dev)
> +		drm_kms_helper_hotplug_event(drm_dev);

[Severity: High]
Can this sequence lead to a use-after-free of the drm_dev pointer?

The drm_dev pointer is extracted under ocm_lock, but the lock is released
before calling drm_kms_helper_hotplug_event(drm_dev) without taking a reference.
If the main DRM display driver is unbound concurrently right after the lock is
released, the drm_device could be destroyed before this worker finishes.

Should the worker acquire a reference with drm_dev_get() under the lock and
drop it after the hotplug event?

[ ... ]
> +static int lt7911exc_dsi_host_attach(struct mipi_dsi_host *host, struct mipi_dsi_device *dev)
> +{
> +	struct lt7911exc *lt7911exc = dsi_host_to_lt7911exc(host);
> +	struct drm_bridge *bridge;
> +	struct drm_panel *panel;
> +	int ret;
> +
> +	if (lt7911exc->output.dev)
> +		return -EBUSY;
> +
> +	ret = drm_of_find_panel_or_bridge(host->dev->of_node, 1, 0, &panel, &bridge);
> +	if (ret)
> +		return ret;
> +
> +	if (panel) {
> +		bridge = devm_drm_panel_bridge_add_typed(lt7911exc->dev, panel,
> +							 DRM_MODE_CONNECTOR_DSI);

[Severity: High]
Does this devm allocation cause a memory leak when the downstream panel unbinds?

The allocated bridge is tied to the lifetime of the host device rather than the
panel. If the panel driver is unbound, lt7911exc_dsi_host_detach() clears the
local pointer, but the bridge remains registered and the memory is not freed.
If the panel binds again, a new bridge is allocated.

Should this use drm_panel_bridge_add_typed() instead?

> +		if (IS_ERR(bridge))
> +			return PTR_ERR(bridge);
> +	}
> +	lt7911exc->output.dev = dev;
> +	lt7911exc->output.bridge = bridge;
> +	lt7911exc->output.panel = panel;
> +
> +	return 0;
> +}
> +
> +static int lt7911exc_dsi_host_detach(struct mipi_dsi_host *host, struct mipi_dsi_device *dev)
> +{
> +	struct lt7911exc *lt7911exc = dsi_host_to_lt7911exc(host);
> +
> +	if (!lt7911exc->output.dev)
> +		return 0;
> +
> +	lt7911exc->output.bridge = NULL;

[Severity: High]
Should this explicitly remove the bridge if it is allocated in attach?

Currently this clears the pointer but leaves the bridge registered in the DRM
core's global bridge list.

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260529112928.873766-1-syyang@lontium.com?part=2