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Message-ID: <608c01c.7716.1958e8d879f.Coremail.andyshrk@163.com>
Date: Thu, 13 Mar 2025 16:09:54 +0800 (CST)
From: "Andy Yan" <andyshrk@....com>
To: "Maxime Ripard" <mripard@...nel.org>
Cc: "Maarten Lankhorst" <maarten.lankhorst@...ux.intel.com>,
"Thomas Zimmermann" <tzimmermann@...e.de>,
"David Airlie" <airlied@...il.com>,
"Simona Vetter" <simona@...ll.ch>,
"Andrzej Hajda" <andrzej.hajda@...el.com>,
"Neil Armstrong" <neil.armstrong@...aro.org>,
"Robert Foss" <rfoss@...nel.org>,
"Laurent Pinchart" <Laurent.pinchart@...asonboard.com>,
"Jonas Karlman" <jonas@...boo.se>,
"Jernej Skrabec" <jernej.skrabec@...il.com>,
"Douglas Anderson" <dianders@...omium.org>,
"Herve Codina" <herve.codina@...tlin.com>,
dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org,
"Dmitry Baryshkov" <dmitry.baryshkov@...aro.org>,
"Simona Vetter" <simona.vetter@...ll.ch>, lumag@...nel.org
Subject: Re:Re:[PATCH v5 04/16] drm/atomic: Introduce helper to lookup
connector by encoder
Hi Maxime,
At 2025-03-05 19:55:19, "Andy Yan" <andyshrk@....com> wrote:
>
>
>Hi Maxime,
>
>At 2025-03-04 19:10:47, "Maxime Ripard" <mripard@...nel.org> wrote:
>>With the bridges switching over to drm_bridge_connector, the direct
>>association between a bridge driver and its connector was lost.
>>
>>This is mitigated for atomic bridge drivers by the fact you can access
>>the encoder, and then call drm_atomic_get_old_connector_for_encoder() or
>>drm_atomic_get_new_connector_for_encoder() with drm_atomic_state.
>>
>>This was also made easier by providing drm_atomic_state directly to all
>>atomic hooks bridges can implement.
>>
>>However, bridge drivers don't have a way to access drm_atomic_state
>>outside of the modeset path, like from the hotplug interrupt path or any
>>interrupt handler.
>>
>>Let's introduce a function to retrieve the connector currently assigned
>>to an encoder, without using drm_atomic_state, to make these drivers'
>>life easier.
>>
>>Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
>>Co-developed-by: Simona Vetter <simona.vetter@...ll.ch>
>>Signed-off-by: Maxime Ripard <mripard@...nel.org>
>>---
>> drivers/gpu/drm/drm_atomic.c | 45 ++++++++++++++++++++++++++++++++++++++++++++
>> include/drm/drm_atomic.h | 3 +++
>> 2 files changed, 48 insertions(+)
>>
>>diff --git a/drivers/gpu/drm/drm_atomic.c b/drivers/gpu/drm/drm_atomic.c
>>index 9ea2611770f43ce7ccba410406d5f2c528aab022..b926b132590e78f8d41d48eb4da4bccf170ee236 100644
>>--- a/drivers/gpu/drm/drm_atomic.c
>>+++ b/drivers/gpu/drm/drm_atomic.c
>>@@ -985,10 +985,55 @@ drm_atomic_get_new_connector_for_encoder(const struct drm_atomic_state *state,
>>
>> return NULL;
>> }
>> EXPORT_SYMBOL(drm_atomic_get_new_connector_for_encoder);
>>
>>+/**
>>+ * drm_atomic_get_connector_for_encoder - Get connector currently assigned to an encoder
>>+ * @encoder: The encoder to find the connector of
>>+ * @ctx: Modeset locking context
>>+ *
>>+ * This function finds and returns the connector currently assigned to
>>+ * an @encoder.
>>+ *
>>+ * Returns:
>>+ * The connector connected to @encoder, or an error pointer otherwise.
>>+ * When the error is EDEADLK, a deadlock has been detected and the
>>+ * sequence must be restarted.
>>+ */
>>+struct drm_connector *
>>+drm_atomic_get_connector_for_encoder(const struct drm_encoder *encoder,
>>+ struct drm_modeset_acquire_ctx *ctx)
>>+{
>>+ struct drm_connector_list_iter conn_iter;
>>+ struct drm_connector *out_connector = ERR_PTR(-EINVAL);
>>+ struct drm_connector *connector;
>>+ struct drm_device *dev = encoder->dev;
>>+ int ret;
>>+
>>+ ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
>>+ if (ret)
>>+ return ERR_PTR(ret);
>
>It seems that this will cause a deadlock when called from a hotplug handling path,
>I have a WIP DP diver[0], which suggested by Dmitry to use this API from a
>&drm_bridge_funcs.detect callback to get the connector, as detect is called by drm_helper_probe_detect,
>which will hold connection_mutex first, so the deaklock happens:
>
>
>drm_helper_probe_detect(struct drm_connector *connector,
> struct drm_modeset_acquire_ctx *ctx,
> bool force)
>{
> const struct drm_connector_helper_funcs *funcs = connector->helper_private;
> struct drm_device *dev = connector->dev;
> int ret;
>
> if (!ctx)
> return drm_helper_probe_detect_ctx(connector, force);
>
> ret = drm_modeset_lock(&dev->mode_config.connection_mutex, ctx);
> if (ret)
> return ret;
>
> if (funcs->detect_ctx)
> ret = funcs->detect_ctx(connector, ctx, force);
> else if (connector->funcs->detect)
> ret = connector->funcs->detect(connector, force);
> else
> ret = connector_status_connected;
>
> if (ret != connector->status)
> connector->epoch_counter += 1;
>
>So I wonder can we let drm_bridge_funcs.detect pass a connector for this case ?
>
>
>
>[0]https://lore.kernel.org/linux-rockchip/047EECFC-7E55-44EC-896F-13FE04333E4D@gmail.com/T/#m25bc53b79f5cc7bddfcb7aae5656f68df396f094
>>+
>>+ drm_connector_list_iter_begin(dev, &conn_iter);
>>+ drm_for_each_connector_iter(connector, &conn_iter) {
>>+ if (!connector->state)
>>+ continue;
>>+
>>+ if (encoder == connector->state->best_encoder) {
>>+ out_connector = connector;
When try to use this patch in my bridge driver, I found that the connector->state->best_encoder
maybe NULL when drm_bridge_funcs.detect or drm_bridge_funcs.detect_ctx is called:
[ 52.713030] Invalid return value -22 for connector detection
[ 52.713539] WARNING: CPU: 7 PID: 288 at drivers/gpu/drm/drm_probe_helper.c:602 drm_helper_probe_single_connector_modes+0x5e0/
0x63c
[ 52.714568] Modules linked in:
[ 52.724546] Call trace:
[ 52.724762] drm_helper_probe_single_connector_modes+0x5e0/0x63c (P)
[ 52.725319] drm_mode_getconnector+0x2a4/0x488
[ 52.725711] drm_ioctl_kernel+0xb4/0x11c
[ 52.726057] drm_ioctl+0x22c/0x544
[ 52.726358] __arm64_sys_ioctl+0xac/0xe0
[ 52.726706] invoke_syscall+0x44/0x100
[ 52.727039] el0_svc_common.constprop.0+0x3c/0xd4
This is because best_encoder is set by set_best_encoder, which is called from
drm_atomic_helper_check_modeset. When we call drm_mode_getconnector
for the first time, the functions mentioned above have not been called yet,
then we can't match the encoder from connector->state->best_encoder for this case.
>>+ break;
>>+ }
>>+ }
>>+ drm_connector_list_iter_end(&conn_iter);
>>+ drm_modeset_unlock(&dev->mode_config.connection_mutex);
>>+
>>+ return out_connector;
>>+}
>>+EXPORT_SYMBOL(drm_atomic_get_connector_for_encoder);
>>+
>>+
>> /**
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