Re: [RFC PATCH v2 2/3] drm/bridge: cadence: cdns-mhdp8546*: Change drm_connector from pointer to structure

[Jayesh Choudhary]

Hi,

On 27/05/25 17:07, Tomi Valkeinen wrote:

Hi,

On 27/05/2025 13:39, Jayesh Choudhary wrote:

On 27/05/25 14:59, Jayesh Choudhary wrote:

Hello Tomi,

On 27/05/25 13:28, Tomi Valkeinen wrote:

Hi,

On 21/05/2025 10:32, Jayesh Choudhary wrote:

After adding DBANC framework, mhdp->connector is not initialised during
bridge calls. But the asyncronous work scheduled depends on the
connector.
We cannot get to drm_atomic_state in these asyncronous calls running on
worker threads. So we need to store the data that we need in mhdp
bridge
structure.
Like other bridge drivers, use drm_connector pointer instead of
structure
and make appropriate changes to the conditionals and assignments
related
to mhdp->connector.
Also, in the atomic enable call, move the connector  and connector
state
calls above, so that we do have a connector before we can retry the
asyncronous work in case of any failure.

I don't quite understand this patch. You change the mhdp->connector to a
pointer, which is set at bridge_enable and cleared at bridge_disable.
Then you change the "mhdp->connector.dev" checks to "mhdp->connector".

So, now in e.g. cdns_mhdp_fw_cb(), we check for mhdp->connector, which
is set at bridge_enable(). Can we ever have the bridge enabled before
the fb has been loaded? What is the check even supposed to do there?

Another in cdns_mhdp_hpd_work(), it checks for mhdp->connector. So...
HPD code behaves differently based on if the bridge has been enabled or
not? What is it supposed to do?

Isn't the whole "if (mhdp->connector.dev)" code for the legacy
non-DRM_BRIDGE_ATTACH_NO_CONNECTOR case?

   Tomi

I misinterpreted your comment in v1[0] regarding finding the connector
from the current state in cdns_mhdp_modeset_retry_fn() and I missed
this. I was more focused on finding a connector for that function.

For the current code, in all the conditionals involving mhdp->connector,
we are entering else statements as connector is not initialised.
So I will just drop if statements in cdns_mhdp_fw_cb() and
cdns_mhdp_hpd_work() (like you said, its legacy case) while still having
mhdp->connector as pointer as we need it for
cdns_mhdp_modeset_retry_fn() and in cdns-mhdp8546-hdcp driver.

That should be okay?

[0]: https://lore.kernel.org/all/e76f94b9-b138-46e7-bb18-
b33dd98c9...@ideasonboard.com/

Warm Regards,
Jayesh

Tomi,

One more thing here. Should this be squashed with the first patch as
this is sort of removing !(DRM_BRIDGE_ATTACH_NO_CONNECTOR) case and
associated changes?

All the legacy code should be removed in the previous patch, yes. But
it's not quite clear to me what's going on here. At least parts of this
patch seem to be... fixing some previous code? You move the
drm_atomic_get_new_connector_for_encoder() call to be earlier in the
bridge_enable. That doesn't sound like removing the legacy code. But
it's not quite clear to me why that's done (or why it wasn't needed
earlier. or was it?).

  Tomi

drm_atomic_get_new_connector_for_encoder() call is moved earlier
in bridge_enable to address the cases when we get error in
cdns_mhdp_link_up(mhdp) or cdns_mhdp_reg_read(mhdp, CDNS_DPTX_CAR,
&resp), and we goto 'out' to schedule modeset_retry_work. We need to
have drm_connector before that if we want to change the connector
link state here.

In legacy usecase we are not hitting this as attach already initialised
mhdp->connector before bridge_enable() that would be used by
cdns_mhdp_modeset_retry_fn() as required.

These errors usually don't hit during bridge_enable calls but in
one of my boards, I saw cdns_mhdp_link_up() giving error and after
that the null pointer dereference in cdns_mhdp_modeset_retry_fn()
while trying to access the mutex there (&conn->dev->mode_config.mutex)

-Jayesh

Fixes: fb43aa0acdfd ("drm: bridge: Add support for Cadence MHDP8546
DPI/DP bridge")
Signed-off-by: Jayesh Choudhary <j-choudh...@ti.com>
---
   .../drm/bridge/cadence/cdns-mhdp8546-core.c   | 28 ++++++++
+----------
   .../drm/bridge/cadence/cdns-mhdp8546-core.h   |  2 +-
   .../drm/bridge/cadence/cdns-mhdp8546-hdcp.c   |  8 +++---
   3 files changed, 19 insertions(+), 19 deletions(-)

diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c b/
drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
index 66bd916c2fe9..5388e62f230b 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.c
@@ -740,7 +740,7 @@ static void cdns_mhdp_fw_cb(const struct
firmware *fw, void *context)
       bridge_attached = mhdp->bridge_attached;
       spin_unlock(&mhdp->start_lock);
       if (bridge_attached) {
-        if (mhdp->connector.dev)
+        if (mhdp->connector)
               drm_kms_helper_hotplug_event(mhdp->bridge.dev);
           else
               drm_bridge_hpd_notify(&mhdp->bridge,
cdns_mhdp_detect(mhdp));
@@ -1759,17 +1759,25 @@ static void cdns_mhdp_atomic_enable(struct
drm_bridge *bridge,
       struct cdns_mhdp_device *mhdp = bridge_to_mhdp(bridge);
       struct cdns_mhdp_bridge_state *mhdp_state;
       struct drm_crtc_state *crtc_state;
-    struct drm_connector *connector;
       struct drm_connector_state *conn_state;
       struct drm_bridge_state *new_state;
       const struct drm_display_mode *mode;
       u32 resp;
-    int ret;
+    int ret = 0;
       dev_dbg(mhdp->dev, "bridge enable\n");
       mutex_lock(&mhdp->link_mutex);
+    mhdp->connector = drm_atomic_get_new_connector_for_encoder(state,
+                                   bridge->encoder);
+    if (WARN_ON(!mhdp->connector))
+        goto out;
+
+    conn_state = drm_atomic_get_new_connector_state(state, mhdp-

connector);

+    if (WARN_ON(!conn_state))
+        goto out;
+
       if (mhdp->plugged && !mhdp->link_up) {
           ret = cdns_mhdp_link_up(mhdp);
           if (ret < 0)
@@ -1789,15 +1797,6 @@ static void cdns_mhdp_atomic_enable(struct
drm_bridge *bridge,
       cdns_mhdp_reg_write(mhdp, CDNS_DPTX_CAR,
                   resp | CDNS_VIF_CLK_EN | CDNS_VIF_CLK_RSTN);
-    connector = drm_atomic_get_new_connector_for_encoder(state,
-                                 bridge->encoder);
-    if (WARN_ON(!connector))
-        goto out;
-
-    conn_state = drm_atomic_get_new_connector_state(state, connector);
-    if (WARN_ON(!conn_state))
-        goto out;
-
       if (mhdp->hdcp_supported &&
           mhdp->hw_state == MHDP_HW_READY &&
           conn_state->content_protection ==
@@ -1857,6 +1856,7 @@ static void cdns_mhdp_atomic_disable(struct
drm_bridge *bridge,
           cdns_mhdp_hdcp_disable(mhdp);
       mhdp->bridge_enabled = false;
+    mhdp->connector = NULL;
       cdns_mhdp_reg_read(mhdp, CDNS_DP_FRAMER_GLOBAL_CONFIG, &resp);
       resp &= ~CDNS_DP_FRAMER_EN;
       resp |= CDNS_DP_NO_VIDEO_MODE;
@@ -2157,7 +2157,7 @@ static void cdns_mhdp_modeset_retry_fn(struct
work_struct *work)
       mhdp = container_of(work, typeof(*mhdp), modeset_retry_work);
-    conn = &mhdp->connector;
+    conn = mhdp->connector;
       /* Grab the locks before changing connector property */
       mutex_lock(&conn->dev->mode_config.mutex);
@@ -2234,7 +2234,7 @@ static void cdns_mhdp_hpd_work(struct
work_struct *work)
       int ret;
       ret = cdns_mhdp_update_link_status(mhdp);
-    if (mhdp->connector.dev) {
+    if (mhdp->connector) {
           if (ret < 0)
               schedule_work(&mhdp->modeset_retry_work);
           else
diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.h b/
drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.h
index bad2fc0c7306..b297db53ba28 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.h
+++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-core.h
@@ -375,7 +375,7 @@ struct cdns_mhdp_device {
        */
       struct mutex link_mutex;
-    struct drm_connector connector;
+    struct drm_connector *connector;
       struct drm_bridge bridge;
       struct cdns_mhdp_link link;
diff --git a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-hdcp.c b/
drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-hdcp.c
index 42248f179b69..59f18c3281ef 100644
--- a/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-hdcp.c
+++ b/drivers/gpu/drm/bridge/cadence/cdns-mhdp8546-hdcp.c
@@ -394,7 +394,7 @@ static int _cdns_mhdp_hdcp_disable(struct
cdns_mhdp_device *mhdp)
       int ret;
       dev_dbg(mhdp->dev, "[%s:%d] HDCP is being disabled...\n",
-        mhdp->connector.name, mhdp->connector.base.id);
+        mhdp->connector->name, mhdp->connector->base.id);
       ret = cdns_mhdp_hdcp_set_config(mhdp, 0, false);
@@ -445,7 +445,7 @@ static int cdns_mhdp_hdcp_check_link(struct
cdns_mhdp_device *mhdp)
       dev_err(mhdp->dev,
           "[%s:%d] HDCP link failed, retrying authentication\n",
-        mhdp->connector.name, mhdp->connector.base.id);
+        mhdp->connector->name, mhdp->connector->base.id);
       ret = _cdns_mhdp_hdcp_disable(mhdp);
       if (ret) {
@@ -487,13 +487,13 @@ static void cdns_mhdp_hdcp_prop_work(struct
work_struct *work)
       struct cdns_mhdp_device *mhdp = container_of(hdcp,
                                struct cdns_mhdp_device,
                                hdcp);
-    struct drm_device *dev = mhdp->connector.dev;
+    struct drm_device *dev = mhdp->connector->dev;
       struct drm_connector_state *state;
       drm_modeset_lock(&dev->mode_config.connection_mutex, NULL);
       mutex_lock(&mhdp->hdcp.mutex);
       if (mhdp->hdcp.value != DRM_MODE_CONTENT_PROTECTION_UNDESIRED) {
-        state = mhdp->connector.state;
+        state = mhdp->connector->state;
           state->content_protection = mhdp->hdcp.value;
       }
       mutex_unlock(&mhdp->hdcp.mutex);