On Fri, Mar 14, 2025 at 09:59:36AM +0200, Dmitry Baryshkov wrote: > On Fri, Mar 14, 2025 at 08:45:17AM +0100, Maxime Ripard wrote: > > On Fri, Mar 14, 2025 at 07:52:35AM +0200, Dmitry Baryshkov wrote: > > > On Fri, Mar 14, 2025 at 08:50:29AM +0800, Andy Yan wrote: > > > > At 2025-03-13 19:55:33, "Maxime Ripard" <mripard@xxxxxxxxxx> wrote: > > > > >Hi, > > > > > > > > > >On Thu, Mar 13, 2025 at 04:09:54PM +0800, Andy Yan wrote: > > > > >> At 2025-03-05 19:55:19, "Andy Yan" <andyshrk@xxxxxxx> wrote: > > > > >> >At 2025-03-04 19:10:47, "Maxime Ripard" <mripard@xxxxxxxxxx> 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@xxxxxxxxxx> > > > > >> >>Co-developed-by: Simona Vetter <simona.vetter@xxxxxxxx> > > > > >> >>Signed-off-by: Maxime Ripard <mripard@xxxxxxxxxx> > > > > >> >>--- > > > > >> >> 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@xxxxxxxxx/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. > > > > > > > > > >As far as I'm concerned, it's by design. Encoders and connectors have > > > > >1:N relationship, and only once a connector has been enabled it has an > > > > >encoder. > > > > > > > > > >If the connector is disabled, there's no associated encoder. > > > > > > > > Does this prove that this API is not suitable for my application scenario: > > > > Get the connector in the bridge's .detect callback, so this means that I may > > > > still need to modify the bridge's connector callback so that it can pass the connector ? > > > > > > I'd say, yes, please. > > > > And I'd say no :) > > Fair enough :-) > > > There's no reason to deviate from the API other entities have here. It's > > just that the switch to DRM_BRIDGE_ATTACH_NO_CONNECTOR hasn't been > > completely thought through and it's one of the part where it shows. > > > > We have two alternative solutions: Either the driver creates the > > connector itself, since it doesn't seem to use any downstream bridge > > anyway, or we need a new bridge helper to find the connector on a bridge > > chain. > > > > We have the iterator already, we just need a new accessor to retrieve > > the (optional) connector of a bridge, and if there's none, go to the > > next bridge and try again. > > The problem is that there is no guarantee that the the created connector > is created for or linked to any bridge. For example, for msm driver I'm > waiting for several series to go in, but after that I plan to work on > moving connector creation to the generic code within the msm driver. > > In other words, with DRM_BRIDGE_ATTACH_NO_CONNECTOR in place it is > perfectly legit not to have a bridge which has "connector of a bridge". > It is possible to create drm_bridge_connector on the drm_encoder's side > after the drm_bridge_attach() succeeds. Sure, but then I'd expect detect and get_modes to only be called *after* that connector has been created, right? Returning NULL in the case where we don't have a connector (yet?) in such a case would make total sense to me, just like we return NULL if the connector is disabled and doesn't have an encoder here. Maxime
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