From e72c3d6502a213ff3db49d70ef985c614512e4e5 Mon Sep 17 00:00:00 2001
From: Douglas Anderson <dianders@chromium.org>
Date: Tue, 13 Jun 2023 06:58:13 -0700
Subject: drm/bridge: ti-sn65dsi86: Fix auxiliary bus lifetime
Git-commit: 7aa83fbd712a6f08ffa67890061f26d140c2a84f
Patch-mainline: v6.5-rc2
References: jsc#PED-3527 jsc#PED-5475 jsc#PED-6068 jsc#PED-6070 jsc#PED-6116 jsc#PED-6120 jsc#PED-5065 jsc#PED-5477 jsc#PED-5511 jsc#PED-6041 jsc#PED-6069 jsc#PED-6071

Memory for the "struct device" for any given device isn't supposed to
be released until the device's release() is called. This is important
because someone might be holding a kobject reference to the "struct
device" and might try to access one of its members even after any
other cleanup/uninitialization has happened.

Code analysis of ti-sn65dsi86 shows that this isn't quite right. When
the code was written, it was believed that we could rely on the fact
that the child devices would all be freed before the parent devices
and thus we didn't need to worry about a release() function. While I
still believe that the parent's "struct device" is guaranteed to
outlive the child's "struct device" (because the child holds a kobject
reference to the parent), the parent's "devm" allocated memory is a
different story. That appears to be freed much earlier.

Let's make this better for ti-sn65dsi86 by allocating each auxiliary
with kzalloc and then free that memory in the release().

Fixes: bf73537f411b ("drm/bridge: ti-sn65dsi86: Break GPIO and MIPI-to-eDP bridge into sub-drivers")
Suggested-by: Stephen Boyd <swboyd@chromium.org>
Reviewed-by: Stephen Boyd <swboyd@chromium.org>
Signed-off-by: Douglas Anderson <dianders@chromium.org>
Link: https://patchwork.freedesktop.org/patch/msgid/20230613065812.v2.1.I24b838a5b4151fb32bccd6f36397998ea2df9fbb@changeid
Acked-by: Patrik Jakobsson <pjakobsson@suse.de>
---
 drivers/gpu/drm/bridge/ti-sn65dsi86.c | 35 +++++++++++++++++----------
 1 file changed, 22 insertions(+), 13 deletions(-)

diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
index 4676cf2900df..3c8fd6ea6d6a 100644
--- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
+++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
@@ -170,10 +170,10 @@
  * @pwm_refclk_freq: Cache for the reference clock input to the PWM.
  */
 struct ti_sn65dsi86 {
-	struct auxiliary_device		bridge_aux;
-	struct auxiliary_device		gpio_aux;
-	struct auxiliary_device		aux_aux;
-	struct auxiliary_device		pwm_aux;
+	struct auxiliary_device		*bridge_aux;
+	struct auxiliary_device		*gpio_aux;
+	struct auxiliary_device		*aux_aux;
+	struct auxiliary_device		*pwm_aux;
 
 	struct device			*dev;
 	struct regmap			*regmap;
@@ -468,27 +468,34 @@ static void ti_sn65dsi86_delete_aux(void *data)
 	auxiliary_device_delete(data);
 }
 
-/*
- * AUX bus docs say that a non-NULL release is mandatory, but it makes no
- * sense for the model used here where all of the aux devices are allocated
- * in the single shared structure. We'll use this noop as a workaround.
- */
-static void ti_sn65dsi86_noop(struct device *dev) {}
+static void ti_sn65dsi86_aux_device_release(struct device *dev)
+{
+	struct auxiliary_device *aux = container_of(dev, struct auxiliary_device, dev);
+
+	kfree(aux);
+}
 
 static int ti_sn65dsi86_add_aux_device(struct ti_sn65dsi86 *pdata,
-				       struct auxiliary_device *aux,
+				       struct auxiliary_device **aux_out,
 				       const char *name)
 {
 	struct device *dev = pdata->dev;
+	struct auxiliary_device *aux;
 	int ret;
 
+	aux = kzalloc(sizeof(*aux), GFP_KERNEL);
+	if (!aux)
+		return -ENOMEM;
+
 	aux->name = name;
 	aux->dev.parent = dev;
-	aux->dev.release = ti_sn65dsi86_noop;
+	aux->dev.release = ti_sn65dsi86_aux_device_release;
 	device_set_of_node_from_dev(&aux->dev, dev);
 	ret = auxiliary_device_init(aux);
-	if (ret)
+	if (ret) {
+		kfree(aux);
 		return ret;
+	}
 	ret = devm_add_action_or_reset(dev, ti_sn65dsi86_uninit_aux, aux);
 	if (ret)
 		return ret;
@@ -497,6 +504,8 @@ static int ti_sn65dsi86_add_aux_device(struct ti_sn65dsi86 *pdata,
 	if (ret)
 		return ret;
 	ret = devm_add_action_or_reset(dev, ti_sn65dsi86_delete_aux, aux);
+	if (!ret)
+		*aux_out = aux;
 
 	return ret;
 }
-- 
2.42.0