`vc4_hdmi_audio_init` calls `devm_snd_dmaengine_pcm_register` which may return EPROBE_DEFER. Calling `drm_connector_hdmi_audio_init` adds a child device. The driver model docs[1] state that adding a child device prior to returning EPROBE_DEFER may result in an infinite loop.
[1] https://www.kernel.org/doc/html/v6.14/driver-api/driver-model/driver.html Fixes: 9640f1437a ("drm/vc4: hdmi: switch to using generic HDMI Codec infrastructure") Signed-off-by: Gabriel Dalimonte <gabriel.dalimo...@gmail.com> --- Starting with v6.14, my Raspberry Pi 4B on the mainline kernel started seeing the vc4 driver looping during probe with: vc4-drm gpu: bound fe400000.hvs (ops vc4_hvs_ops [vc4]) Registered IR keymap rc-cec rc rc0: vc4-hdmi-0 as /devices/platform/soc/fef00700.hdmi/rc/rc0 input: vc4-hdmi-0 as /devices/platform/soc/fef00700.hdmi/rc/rc0/input3503 vc4_hdmi fef00700.hdmi: Could not register PCM component: -517 repeating several times per second. >From my understanding, this happens when the sound subsystem can't create a device, thus returning -517 (EPROBE_DEFER). All of this is consistent with what I experienced prior to 6.14 as well. However, prior to 6.14 it did not try to probe infinitely. Bisecting 6.13 -> 6.14, it looks like 9640f1437a88d8c617ff5523f1f9dc8c3ff29121 [1] moved HDMI audio connector initialization from vc4 audio initialization to vc4 connector initialization. If my understanding is correct, this change causes a child device to be added before EPROBE_DEFER is returned and queues the device probe to happen when a new device is added, which happens immediately because the audio child device was added earlier in the probe. [1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/?id=9640f1437a88d8c617ff5523f1f9dc8c3ff29121 --- Changes in v2: - Add Fixes: tag - Link to v1: https://lore.kernel.org/r/20250426-vc4-audio-inf-probe-v1-1-a500785b7...@gmail.com --- drivers/gpu/drm/vc4/vc4_hdmi.c | 12 ++++++------ 1 file changed, 6 insertions(+), 6 deletions(-) diff --git a/drivers/gpu/drm/vc4/vc4_hdmi.c b/drivers/gpu/drm/vc4/vc4_hdmi.c index a29a6ef266f9a5952af53030a9a2d313e2ecdfce..163d092bd973bb3dfc5ea61187ec5fdf4f4f6029 100644 --- a/drivers/gpu/drm/vc4/vc4_hdmi.c +++ b/drivers/gpu/drm/vc4/vc4_hdmi.c @@ -560,12 +560,6 @@ static int vc4_hdmi_connector_init(struct drm_device *dev, if (ret) return ret; - ret = drm_connector_hdmi_audio_init(connector, dev->dev, - &vc4_hdmi_audio_funcs, - 8, false, -1); - if (ret) - return ret; - drm_connector_helper_add(connector, &vc4_hdmi_connector_helper_funcs); /* @@ -2291,6 +2285,12 @@ static int vc4_hdmi_audio_init(struct vc4_hdmi *vc4_hdmi) return ret; } + ret = drm_connector_hdmi_audio_init(&vc4_hdmi->connector, dev, + &vc4_hdmi_audio_funcs, 8, false, + -1); + if (ret) + return ret; + dai_link->cpus = &vc4_hdmi->audio.cpu; dai_link->codecs = &vc4_hdmi->audio.codec; dai_link->platforms = &vc4_hdmi->audio.platform; --- base-commit: b60301774a8fe6c30b14a95104ec099290a2e904 change-id: 20250426-vc4-audio-inf-probe-f67a8aa2a180 Best regards, -- Gabriel Dalimonte <gabriel.dalimo...@gmail.com>
