[PATCH v5 0/2] drm/bridge: ti-sn65dsi83: Various fixes

[PATCH v5 0/2] drm/bridge: ti-sn65dsi83: Various fixes

[Esben Haabendal]

This small series adds support for using SN65DSI84 in single-link mode with
output to LVDS channel B, and provides a fix for an error-handling
regression in sn65dsi83_reset_pipe()/sn65dsi83_reset_work().

Signed-off-by: Esben Haabendal <esben@geanix.com>
---
Changes in v5:
- Squashed patch 1 and 2 and changed it so that enable_irq() is only called
  when sn65dsi83_reset_pipe() succeeds.
- Link to v4: https://patch.msgid.link/20260810-ti-sn65dsi83-fixes-v4-0-ae9c95c8d162@geanix.com

Changes in v4:
- Swapped patch 1 and 2 for proper ordering.
- Ensure enable_irq() is called in sn65dsi83_reset_work() error handling
  path.
- Added Fixes and Cc: stable tags to patch 1 and 2.
- Link to v3: https://patch.msgid.link/20260803-ti-sn65dsi83-fixes-v3-0-9b403a405ccd@geanix.com

Changes in v3:
- Rename panel_port variable to output_port.
- Propagate error code from drm_bridge_helper_reset_crtc() in
  sn65dsi83_reset_pipe().
- Drop with fix for premature PLL locking. Should be fixed in DSI host
  driver (or upstream bridge driver) instead.
  See https://lore.kernel.org/all/48f6f55f-43fd-4355-88b9-d2e2d0e26d07@kontron.de/
- Link to v2: https://patch.msgid.link/20260715-ti-sn65dsi83-fixes-v2-0-ebc4c3fe29b6@geanix.com

Changes in v2:
- Fix error handling in sn65dsi83_atomic_enable() to ensure
  drm_brige_exit() is always called on exit.
- Change logging level from warn to dbg for two messages in
  sn65dsi83_parse_dt().
- Removed trailing dot in comment lines.
- Added patch with fix so that DRM bridge critical section is exited on
  error in sn65dsi83_reset_work().
- Added Fixes and Cc: stable tags to the premature PLL patch.
- Re-ordered patch so fixes comes first.
- Link to v1: https://patch.msgid.link/20260711-ti-sn65dsi83-fixes-v1-0-d85eb5342b98@geanix.com

To: Luca Ceresoli <luca.ceresoli@bootlin.com>
To: Herve Codina <herve.codina@bootlin.com>
To: Andrzej Hajda <andrzej.hajda@intel.com>
To: Neil Armstrong <neil.armstrong@linaro.org>
To: Robert Foss <rfoss@kernel.org>
To: Laurent Pinchart <Laurent.pinchart@ideasonboard.com>
To: Jonas Karlman <jonas@kwiboo.se>
To: Jernej Skrabec <jernej.skrabec@gmail.com>
To: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
To: Maxime Ripard <mripard@kernel.org>
To: Thomas Zimmermann <tzimmermann@suse.de>
To: David Airlie <airlied@gmail.com>
To: Simona Vetter <simona@ffwll.ch>
To: Linus Walleij <linusw@kernel.org>
To: Frieder Schrempf <frieder.schrempf@kontron.de>
To: Marek Vasut <marex@denx.de>
To: Dmitry Baryshkov <lumag@kernel.org>
Cc: dri-devel@lists.freedesktop.org
Cc: linux-kernel@vger.kernel.org

---
Esben Haabendal (2):
      drm/bridge: ti-sn65dsi83: Fix error handling in sn65dsi83_reset_work()
      drm/bridge: ti-sn65dsi83: Support LVDS Channel B on SN65DSI84

 drivers/gpu/drm/bridge/ti-sn65dsi83.c | 40 +++++++++++++++++++++++------------
 1 file changed, 27 insertions(+), 13 deletions(-)
---
base-commit: 8d3ae59288f1e7d58d76558a6ee96d533bc5019f
change-id: 20260710-ti-sn65dsi83-fixes-1d08e0ac67b3

Best regards,
--  
Esben Haabendal <esben@geanix.com>

[PATCH v5 1/2] drm/bridge: ti-sn65dsi83: Fix error handling in sn65dsi83_reset_work()

[Esben Haabendal]

The error handling of sn65dsi83_reset_pipe() in sn65dsi83_reset_work() has
seen a couple of changes that seems to cause a bit of confusion.

While sn65dsi83_reset_work() has implemented an early exit if
sn65dsi83_reset_pipe() fails since it was added, when a commit from Maxime
Ripard switched to use drm_bridge_helper_reset_crtc() [1] the
sn65dsi83_reset_pipe() function would no longer return an error code, so
the early exit was then a no-op, and even on sn65dsi83_reset_pipe()
failure, enable_irq() has been called.

When drm_bridge_enter()/drm_bridge_exit() resource protection was added,
the drm_bridge_exit() incidentally was always called, which is the correct
approach. But only because the early exit in sn65dsi83_reset_pipe() was
never hit because sn65dsi83_reset_pipe() always returns 0.

In order get back to a situation where enable_irq() is not called on
sn65dsi83_reset_pipe() failure, which should help protect against irq
storms, we need to reintroduce a non-zero return value from
sn65dsi83_reset_pipe() on error, and fix sn65dsi83_reset_work() so that we
always exit the DRM bridge critical section with drm_bridge_exit().

[1] commit e17fadff7ab9 ("drm/bridge: ti-sn65dsi83: Switch to drm_bridge_helper_reset_crtc")
[2] commit d2e8d1bc840b ("drm/bridge: ti-sn65dsi83: protect device resources on unplug")

Fixes: e17fadff7ab9 ("drm/bridge: ti-sn65dsi83: Switch to drm_bridge_helper_reset_crtc")
Cc: stable@vger.kernel.org
Signed-off-by: Esben Haabendal <esben@geanix.com>
---
 drivers/gpu/drm/bridge/ti-sn65dsi83.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
index 42b451432bbb..9f530cd05d2f 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
@@ -403,7 +403,7 @@ static int sn65dsi83_reset_pipe(struct sn65dsi83 *sn65dsi83)
 	drm_modeset_drop_locks(&ctx);
 	drm_modeset_acquire_fini(&ctx);
 
-	return 0;
+	return err;
 }
 
 static void sn65dsi83_reset_work(struct work_struct *ws)
@@ -419,11 +419,13 @@ static void sn65dsi83_reset_work(struct work_struct *ws)
 	ret = sn65dsi83_reset_pipe(ctx);
 	if (ret) {
 		dev_err(ctx->dev, "reset pipe failed %pe\n", ERR_PTR(ret));
-		return;
+		goto bridge_exit;
 	}
+
 	if (ctx->irq)
 		enable_irq(ctx->irq);
 
+bridge_exit:
 	drm_bridge_exit(idx);
 }
 

-- 
2.55.0

[PATCH v5 2/2] drm/bridge: ti-sn65dsi83: Support LVDS Channel B on SN65DSI84

[Esben Haabendal]

Add support for using SN65DSI84 in single-link mode with output to LVDS
Channel B.

Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Signed-off-by: Esben Haabendal <esben@geanix.com>
---
 drivers/gpu/drm/bridge/ti-sn65dsi83.c | 34 +++++++++++++++++++++++-----------
 1 file changed, 23 insertions(+), 11 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
index 9f530cd05d2f..fcbc427947b6 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
@@ -11,6 +11,8 @@
  *   = 1x Single-link DSI ~ 2x Single-link or 1x Dual-link LVDS
  *   - Supported
  *   - Dual-link LVDS mode tested
+ *   - Single-link to LVDS Channel A tested
+ *   - Single-link to LVDS Channel B tested
  *   - 2x Single-link LVDS mode unsupported
  *     (should be easy to add by someone who has the HW)
  * - SN65DSI85
@@ -162,7 +164,7 @@ struct sn65dsi83 {
 	struct gpio_desc		*enable_gpio;
 	struct regulator		*vcc;
 	bool				lvds_dual_link;
-	bool				lvds_dual_link_even_odd_swap;
+	bool				lvds_channel_swap;
 	int				lvds_vod_swing_conf[2];
 	int				lvds_term_conf[2];
 	int				irq;
@@ -644,7 +646,7 @@ static void sn65dsi83_atomic_pre_enable(struct drm_bridge *bridge,
 			REG_LVDS_VCOM_CHA_LVDS_VOD_SWING(ctx->lvds_vod_swing_conf[CHANNEL_A]) |
 			REG_LVDS_VCOM_CHB_LVDS_VOD_SWING(ctx->lvds_vod_swing_conf[CHANNEL_B]));
 	regmap_write(ctx->regmap, REG_LVDS_LANE,
-		     (ctx->lvds_dual_link_even_odd_swap ?
+		     (ctx->lvds_channel_swap ?
 		      REG_LVDS_LANE_EVEN_ODD_SWAP : 0) |
 		     (ctx->lvds_term_conf[CHANNEL_A] ?
 			  REG_LVDS_LANE_CHA_LVDS_TERM : 0) |
@@ -895,6 +897,7 @@ static int sn65dsi83_parse_dt(struct sn65dsi83 *ctx, enum sn65dsi83_model model)
 {
 	struct drm_bridge *panel_bridge;
 	struct device *dev = ctx->dev;
+	u32 output_port = 2;
 	int ret;
 
 	ret = sn65dsi83_parse_lvds_endpoint(ctx, CHANNEL_A);
@@ -906,29 +909,38 @@ static int sn65dsi83_parse_dt(struct sn65dsi83 *ctx, enum sn65dsi83_model model)
 		return ret;
 
 	ctx->lvds_dual_link = false;
-	ctx->lvds_dual_link_even_odd_swap = false;
+	ctx->lvds_channel_swap = false;
 	if (model != MODEL_SN65DSI83) {
-		struct device_node *port2, *port3;
+		struct device_node *port0, *port1, *port2, *port3;
 		int dual_link;
 
+		port0 = of_graph_get_port_by_id(dev->of_node, 0);
+		port1 = of_graph_get_port_by_id(dev->of_node, 1);
 		port2 = of_graph_get_port_by_id(dev->of_node, 2);
 		port3 = of_graph_get_port_by_id(dev->of_node, 3);
 		dual_link = drm_of_lvds_get_dual_link_pixel_order(port2, port3);
-		of_node_put(port2);
-		of_node_put(port3);
 
 		if (dual_link == DRM_LVDS_DUAL_LINK_ODD_EVEN_PIXELS) {
-			ctx->lvds_dual_link = true;
 			/* Odd pixels to LVDS Channel A, even pixels to B */
-			ctx->lvds_dual_link_even_odd_swap = false;
-		} else if (dual_link == DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS) {
 			ctx->lvds_dual_link = true;
+		} else if (dual_link == DRM_LVDS_DUAL_LINK_EVEN_ODD_PIXELS) {
 			/* Even pixels to LVDS Channel A, odd pixels to B */
-			ctx->lvds_dual_link_even_odd_swap = true;
+			ctx->lvds_dual_link = true;
+			ctx->lvds_channel_swap = true;
+		} else if (port0 && !port1 && port2 && !port3) {
+			/* DSI Channel A to LVDS Channel A */
+		} else if (port0 && !port1 && !port2 && port3) {
+			/* DSI Channel A to LVDS Channel B */
+			ctx->lvds_channel_swap = true;
+			output_port = 3;
 		}
+		of_node_put(port0);
+		of_node_put(port1);
+		of_node_put(port2);
+		of_node_put(port3);
 	}
 
-	panel_bridge = devm_drm_of_get_bridge(dev, dev->of_node, 2, 0);
+	panel_bridge = devm_drm_of_get_bridge(dev, dev->of_node, output_port, 0);
 	if (IS_ERR(panel_bridge))
 		return dev_err_probe(dev, PTR_ERR(panel_bridge), "Failed to get panel bridge\n");
 

-- 
2.55.0

Re: [PATCH v5 1/2] drm/bridge: ti-sn65dsi83: Fix error handling in sn65dsi83_reset_work()

[sashiko-bot]

Thank you for your contribution! Sashiko AI review found 1 potential issue(s) to consider:

Pre-existing issues:
- [High] Missing `cancel_work_sync` for `reset_work` leads to a use-after-free on driver unbind.
--

commit 47920da4c643294656a651a954618ec33114a7d9
Author: Esben Haabendal <esben@geanix.com>

drm/bridge: ti-sn65dsi83: Fix error handling in sn65dsi83_reset_work()

The commit reintroduces a non-zero return value from sn65dsi83_reset_pipe()
on error to prevent erroneous IRQ re-enabling during failures. It also
updates sn65dsi83_reset_work() to properly exit the DRM bridge critical
section by always calling drm_bridge_exit().

> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi83.c b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> index 42b451432bbb6..9f530cd05d2f3 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi83.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi83.c
[ ... ]
> @@ -419,11 +419,13 @@ static void sn65dsi83_reset_work(struct work_struct *ws)
>  	ret = sn65dsi83_reset_pipe(ctx);
>  	if (ret) {
>  		dev_err(ctx->dev, "reset pipe failed %pe\n", ERR_PTR(ret));
> -		return;
> +		goto bridge_exit;
>  	}
> +
>  	if (ctx->irq)
>  		enable_irq(ctx->irq);
>  
> +bridge_exit:
>  	drm_bridge_exit(idx);
>  }

[Severity: High]
This isn't a bug introduced by this patch, but I noticed a potential
use-after-free related to the reset_work structure that is being modified here.

During driver unbind (e.g., via sysfs), sn65dsi83_remove() unplugs the bridge
but does not explicitly call cancel_work_sync(&ctx->reset_work). After
sn65dsi83_remove() returns, devres automatically frees the IRQ and the ctx
structure.

If an interrupt had previously scheduled the work, the work item might remain
in the queue and eventually execute sn65dsi83_reset_work(), which will attempt
to access the freed ctx pointer (e.g., when calling
drm_bridge_enter(&ctx->bridge, &idx)).

Should sn65dsi83_remove() be updated to include a call to
cancel_work_sync(&ctx->reset_work) to ensure the work is fully cancelled
before devres tears down the allocated memory?

-- 
Sashiko AI review · https://sashiko.dev/#/patchset/20260831-ti-sn65dsi83-fixes-v5-0-e712765d6c4f@geanix.com?part=1

Re: [PATCH v5 1/2] drm/bridge: ti-sn65dsi83: Fix error handling in sn65dsi83_reset_work()

[Herve Codina]

Hi Esben,

On Mon, 31 Aug 2026 14:21:32 +0200
Esben Haabendal <esben@geanix.com> wrote:

> The error handling of sn65dsi83_reset_pipe() in sn65dsi83_reset_work() has
> seen a couple of changes that seems to cause a bit of confusion.
> 
> While sn65dsi83_reset_work() has implemented an early exit if
> sn65dsi83_reset_pipe() fails since it was added, when a commit from Maxime
> Ripard switched to use drm_bridge_helper_reset_crtc() [1] the
> sn65dsi83_reset_pipe() function would no longer return an error code, so
> the early exit was then a no-op, and even on sn65dsi83_reset_pipe()
> failure, enable_irq() has been called.
> 
> When drm_bridge_enter()/drm_bridge_exit() resource protection was added,
> the drm_bridge_exit() incidentally was always called, which is the correct
> approach. But only because the early exit in sn65dsi83_reset_pipe() was
> never hit because sn65dsi83_reset_pipe() always returns 0.
> 
> In order get back to a situation where enable_irq() is not called on
> sn65dsi83_reset_pipe() failure, which should help protect against irq
> storms, we need to reintroduce a non-zero return value from
> sn65dsi83_reset_pipe() on error, and fix sn65dsi83_reset_work() so that we
> always exit the DRM bridge critical section with drm_bridge_exit().
> 
> [1] commit e17fadff7ab9 ("drm/bridge: ti-sn65dsi83: Switch to drm_bridge_helper_reset_crtc")
> [2] commit d2e8d1bc840b ("drm/bridge: ti-sn65dsi83: protect device resources on unplug")
> 
> Fixes: e17fadff7ab9 ("drm/bridge: ti-sn65dsi83: Switch to drm_bridge_helper_reset_crtc")
> Cc: stable@vger.kernel.org
> Signed-off-by: Esben Haabendal <esben@geanix.com>
> ---
>  drivers/gpu/drm/bridge/ti-sn65dsi83.c | 6 ++++--
>  1 file changed, 4 insertions(+), 2 deletions(-)
> 

LGTM.

Reviewed-by: Herve Codina <herve.codina@bootlin.com>

Best regards,
Hervé

Re: [PATCH v5 1/2] drm/bridge: ti-sn65dsi83: Fix error handling in sn65dsi83_reset_work()

[Luca Ceresoli]

On Mon, 31 Aug 2026 14:21:32 +0200, Esben Haabendal <esben@geanix.com> wrote:
> The error handling of sn65dsi83_reset_pipe() in sn65dsi83_reset_work() has
> seen a couple of changes that seems to cause a bit of confusion.
> 
> While sn65dsi83_reset_work() has implemented an early exit if
> sn65dsi83_reset_pipe() fails since it was added, when a commit from Maxime
> Ripard switched to use drm_bridge_helper_reset_crtc() [1] the
> sn65dsi83_reset_pipe() function would no longer return an error code, so
> the early exit was then a no-op, and even on sn65dsi83_reset_pipe()
> failure, enable_irq() has been called.
> 
> [...]

Reviewed-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
Tested-by: Luca Ceresoli <luca.ceresoli@bootlin.com>

-- 
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

Re: [PATCH v5 1/2] drm/bridge: ti-sn65dsi83: Fix error handling in sn65dsi83_reset_work()

[Luca Ceresoli]

Hi Esben,

On Mon Aug 31, 2026 at 2:21 PM CEST, Esben Haabendal wrote:
> The error handling of sn65dsi83_reset_pipe() in sn65dsi83_reset_work() has
> seen a couple of changes that seems to cause a bit of confusion.
>
> While sn65dsi83_reset_work() has implemented an early exit if
> sn65dsi83_reset_pipe() fails since it was added, when a commit from Maxime
> Ripard switched to use drm_bridge_helper_reset_crtc() [1] the
> sn65dsi83_reset_pipe() function would no longer return an error code, so
> the early exit was then a no-op, and even on sn65dsi83_reset_pipe()
> failure, enable_irq() has been called.
>
> When drm_bridge_enter()/drm_bridge_exit() resource protection was added,
> the drm_bridge_exit() incidentally was always called, which is the correct
> approach. But only because the early exit in sn65dsi83_reset_pipe() was
> never hit because sn65dsi83_reset_pipe() always returns 0.
>
> In order get back to a situation where enable_irq() is not called on
> sn65dsi83_reset_pipe() failure, which should help protect against irq
> storms, we need to reintroduce a non-zero return value from
> sn65dsi83_reset_pipe() on error, and fix sn65dsi83_reset_work() so that we
> always exit the DRM bridge critical section with drm_bridge_exit().
>
> [1] commit e17fadff7ab9 ("drm/bridge: ti-sn65dsi83: Switch to drm_bridge_helper_reset_crtc")
> [2] commit d2e8d1bc840b ("drm/bridge: ti-sn65dsi83: protect device resources on unplug")
>
> Fixes: e17fadff7ab9 ("drm/bridge: ti-sn65dsi83: Switch to drm_bridge_helper_reset_crtc")
> Cc: stable@vger.kernel.org
> Signed-off-by: Esben Haabendal <esben@geanix.com>

Thanks for having sorted out this complicated situation!

Now all patches are approved, so I'll apply them next week if all goes
well. Being one fix and one feature thay'll have to go to different
branches: drm-misc-fixes and drm-misc-next respectively. As I see it, the
two patches are orthogonal, so that shouldn't be a problem.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com