Hello，
At 2025-03-19 03:00:29, "Dmitry Baryshkov" <dmitry.barysh...@oss.qualcomm.com>
wrote:
>On Tue, Mar 18, 2025 at 04:51:19PM +0100, Maxime Ripard wrote:
>> On Fri, Mar 14, 2025 at 08:28:22PM +0200, Dmitry Baryshkov wrote:
>> > On Fri, Mar 14, 2025 at 06:40:24PM +0100, Maxime Ripard wrote:
>> > > 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" <mrip...@kernel.org>
>> > > > > > > wrote:
>> > > > > > > >Hi,
>> > > > > > > >
>> > > > > > > >On Thu, Mar 13, 2025 at 04:09:54PM +0800, Andy Yan wrote:
>> > > > > > > >> At 2025-03-05 19:55:19, "Andy Yan" <andys...@163.com> wrote:
>> > > > > > > >> >At 2025-03-04 19:10:47, "Maxime Ripard" <mrip...@kernel.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.barysh...@linaro.org>
>> > > > > > > >> >>Co-developed-by: Simona Vetter <simona.vet...@ffwll.ch>
>> > > > > > > >> >>Signed-off-by: Maxime Ripard <mrip...@kernel.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-13fe04333...@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.
>> > > > > > > >
>> > > > > > > >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?
>> >
>> > Yes. But you can not get the connector by following bridge chain. Well,
>> > unless you include encoder into the chain. If that's what you have had
>> > in mind, then please excuse me, I didn't understand that from the
>> > beginning.
>>
>> You can't include the encoder either, because the encoder doesn't have a
>> connector assigned yet at that time.
>>
>> However, you can:
>>
>> - Store the bridge attach flags in drm_bridge
>>
>> - Create a hook that returns the connector a bridge creates, depending
>> on the attach flags.
>>
>> - Create a helper that iterates over the next bridges until the
>> previous hook returns !NULL. If it doesn't find anything, return
>> NULL.
>>
>> AFAIK, it solves all the problems being discussed here, while dealing
>> with legacy and new-style bridge drivers.
>
>I'm still fail to understand how does that solve the issue for new-style
>bridges. How do we find the created drm_bridge_connector for them?
>
>>
>> > But frankly speaking, I think it might be easier to pass down the
>> > connector to the detect callback (as drm_connector_funcs.detect already
>> > gets the connecor) rather than making bridge drivers go through the
>> > chain to get the value that is already present in the caller function.
>> >
>> > (For some other usecases I'd totally agree with you, especially if the
>> > connector isn't already available on the caller side).
>>
>> Still, we've tried to converge to the same API for all entities, it
>> feels like a step backward to me.
>
>I'd argue here a bit. The drm_connector interface has connector here.
>drm_bridge is an extension/subpart of the drm_connector, so it would be
>logical to extend that interface.
Yes, since all the calls to drm_bridge_funcs.detect are initiated by the
connecter,
I think it is reasonable to pass this connecter to the corresponding bridge.
And this can prevent iterates failures caused by various complex bridge
connection logic changes.
>
>
>--
>With best wishes
>Dmitry
