From: Imre Deak imre.deak@intel.com

commit fe2352fd64029918174de4b460dfe6df0c6911cd upstream

This is not a clean cherry-pick due to code divergence.

Add a helper to reschedule drm_mode_config::output_poll_work after polling has been enabled for a connector (and needing a reschedule, since previously polling was disabled for all connectors and hence output_poll_work was not running).

This is needed by the next patch fixing HPD polling on i915.

Cc: stable@vger.kernel.org # 6.4+ Cc: Dmitry Baryshkov dmitry.baryshkov@linaro.org Cc: dri-devel@lists.freedesktop.org Reviewed-by: Jouni Högander jouni.hogander@intel.com Reviewed-by: Dmitry Baryshkov dmitry.baryshkov@linaro.org Signed-off-by: Imre Deak imre.deak@intel.com Link: https://patchwork.freedesktop.org/patch/msgid/20230822113015.41224-1-imre.de... Signed-off-by: Nicusor Huhulea nicusor.huhulea@siemens.com --- drivers/gpu/drm/drm_probe_helper.c | 74 +++++++++++++++++++----------- include/drm/drm_probe_helper.h | 1 + 2 files changed, 49 insertions(+), 26 deletions(-)

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c index 0e5eadc6d44d..787f6699971f 100644 --- a/drivers/gpu/drm/drm_probe_helper.c +++ b/drivers/gpu/drm/drm_probe_helper.c @@ -224,6 +224,26 @@ drm_connector_mode_valid(struct drm_connector *connector, }

#define DRM_OUTPUT_POLL_PERIOD (10*HZ) +static void reschedule_output_poll_work(struct drm_device *dev) +{ + unsigned long delay = DRM_OUTPUT_POLL_PERIOD; + + if (dev->mode_config.delayed_event) + /* + * FIXME: + * + * Use short (1s) delay to handle the initial delayed event. + * This delay should not be needed, but Optimus/nouveau will + * fail in a mysterious way if the delayed event is handled as + * soon as possible like it is done in + * drm_helper_probe_single_connector_modes() in case the poll + * was enabled before. + */ + delay = HZ; + + schedule_delayed_work(&dev->mode_config.output_poll_work, delay); +} + /** * drm_kms_helper_poll_enable - re-enable output polling. * @dev: drm_device @@ -244,43 +264,45 @@ drm_connector_mode_valid(struct drm_connector *connector, */ void drm_kms_helper_poll_enable(struct drm_device *dev) { - bool poll = false; + struct drm_connector *connector; struct drm_connector_list_iter conn_iter; - unsigned long delay = DRM_OUTPUT_POLL_PERIOD;

if (drm_WARN_ON_ONCE(dev, !dev->mode_config.poll_enabled) || !drm_kms_helper_poll || dev->mode_config.poll_running) return;

- drm_connector_list_iter_begin(dev, &conn_iter); - drm_for_each_connector_iter(connector, &conn_iter) { - if (connector->polled & (DRM_CONNECTOR_POLL_CONNECT | - DRM_CONNECTOR_POLL_DISCONNECT)) - poll = true; - } - drm_connector_list_iter_end(&conn_iter); + if (drm_kms_helper_enable_hpd(dev) || + dev->mode_config.delayed_event) + reschedule_output_poll_work(dev);

- if (dev->mode_config.delayed_event) { - /* - * FIXME: - * - * Use short (1s) delay to handle the initial delayed event. - * This delay should not be needed, but Optimus/nouveau will - * fail in a mysterious way if the delayed event is handled as - * soon as possible like it is done in - * drm_helper_probe_single_connector_modes() in case the poll - * was enabled before. - */ - poll = true; - delay = HZ; - } - - if (poll) - schedule_delayed_work(&dev->mode_config.output_poll_work, delay); + dev->mode_config.poll_running = true; } EXPORT_SYMBOL(drm_kms_helper_poll_enable);

+/** + * drm_kms_helper_poll_reschedule - reschedule the output polling work + * @dev: drm_device + * + * This function reschedules the output polling work, after polling for a + * connector has been enabled. + * + * Drivers must call this helper after enabling polling for a connector by + * setting %DRM_CONNECTOR_POLL_CONNECT / %DRM_CONNECTOR_POLL_DISCONNECT flags + * in drm_connector::polled. Note that after disabling polling by clearing these + * flags for a connector will stop the output polling work automatically if + * the polling is disabled for all other connectors as well. + * + * The function can be called only after polling has been enabled by calling + * drm_kms_helper_poll_init() / drm_kms_helper_poll_enable(). + */ +void drm_kms_helper_poll_reschedule(struct drm_device *dev) +{ + if (dev->mode_config.poll_running) + reschedule_output_poll_work(dev); +} +EXPORT_SYMBOL(drm_kms_helper_poll_reschedule); + static enum drm_connector_status drm_helper_probe_detect_ctx(struct drm_connector *connector, bool force) { diff --git a/include/drm/drm_probe_helper.h b/include/drm/drm_probe_helper.h index 5880daa14624..429a85f38036 100644 --- a/include/drm/drm_probe_helper.h +++ b/include/drm/drm_probe_helper.h @@ -25,6 +25,7 @@ void drm_kms_helper_connector_hotplug_event(struct drm_connector *connector);

void drm_kms_helper_poll_disable(struct drm_device *dev); void drm_kms_helper_poll_enable(struct drm_device *dev); +void drm_kms_helper_poll_reschedule(struct drm_device *dev); bool drm_kms_helper_is_poll_worker(void);

enum drm_mode_status drm_crtc_helper_mode_valid_fixed(struct drm_crtc *crtc,

From: Dmitry Baryshkov dmitry.baryshkov@linaro.org

commit c8268795c9a9cc7be50f78d4502fad83a2a4f8df upstream

This is not a direct cherry-pick of the upstream commit. Only the helper functions required as dependencies for "drm/i915: Fix HPD polling, reenabling the output poll work as needed" were extracted from the original commit. The rest of the code was not applied, as the codebase has diverged significantly from upstream.

This partial adaptation ensures that the required drm_connector_helper_funcs are available for the dependent fix, while minimizing changes to the existing code.

Introduce two drm_connector_helper_funcs: enable_hpd() and disable_hpd(). They are called by drm_kms_helper_poll_enable() and drm_kms_helper_poll_disable() (and thus drm_kms_helper_poll_init() and drm_kms_helper_poll_fini()) respectively.

This allows DRM drivers to rely on drm_kms_helper_poll for enabling and disabling HPD detection rather than doing that manually.

Signed-off-by: Dmitry Baryshkov dmitry.baryshkov@linaro.org Reviewed-by: Tomi Valkeinen tomi.valkeinen@ideasonboard.com Signed-off-by: Neil Armstrong neil.armstrong@linaro.org Link: https://patchwork.freedesktop.org/patch/msgid/20221102180705.459294-3-dmitry... Signed-off-by: Nicusor Huhulea nicusor.huhulea@siemens.com --- include/drm/drm_modeset_helper_vtables.h | 22 ++++++++++++++++++++++ 1 file changed, 22 insertions(+)

diff --git a/include/drm/drm_modeset_helper_vtables.h b/include/drm/drm_modeset_helper_vtables.h index 6f19cf5c210e..54f4848a655a 100644 --- a/include/drm/drm_modeset_helper_vtables.h +++ b/include/drm/drm_modeset_helper_vtables.h @@ -1144,6 +1144,28 @@ struct drm_connector_helper_funcs { */ void (*cleanup_writeback_job)(struct drm_writeback_connector *connector, struct drm_writeback_job *job); + + /** + * @enable_hpd: + * + * Enable hot-plug detection for the connector. + * + * This operation is optional. + * + * This callback is used by the drm_kms_helper_poll_enable() helpers. + */ + void (*enable_hpd)(struct drm_connector *connector); + + /** + * @disable_hpd: + * + * Disable hot-plug detection for the connector. + * + * This operation is optional. + * + * This callback is used by the drm_kms_helper_poll_disable() helpers. + */ + void (*disable_hpd)(struct drm_connector *connector); };

/**

Hi Nicusor,

thanks for the report and the root causing effort. The patchset itself has a few issues:

- commit cfd48ad8c4a9 ("drm/i915: Fix HPD polling, reenabling the output poll work as needed") you backport fixes d33a54e3991d ("drm/probe_helper: sort out poll_running vs poll_enabled"), but this fixed commit is not part of the 6.1.y stable tree which you are targeting.

Similarly commit d33a54e3991d fixes c8268795c9a9 ("drm/probe-helper: enable and disable HPD on connectors"), which is not part of 6.1.y either.

This means the issue commit cfd48ad8c4a9 is fixing is not present in the 6.1.y tree, as the changes introducing that issue are not present in that tree either.

- The compile errors the patches in your patchset introduce would prevent bisection, so fixing up these compile errors only at the end of the patchset is not ok; the tree should compile without errors at each patch/commit.

Looking at v6.1.y and the patchset I suspect the actual issue is the

commit 4ad8d57d902f ("drm: Check output polling initialized before disabling") backport in v6.1.y, which had the

- if (!dev->mode_config.poll_enabled || !drm_kms_helper_poll) + if (drm_WARN_ON_ONCE(dev, !dev->mode_config.poll_enabled) || + !drm_kms_helper_poll || dev->mode_config.poll_running)

change, not part of the original

commit 5abffb66d12b ("drm: Check output polling initialized before disabling"). i.e. the original patch didn't add the check for dev->mode_config.poll_running. So could you try on top of v6.1.147 (w/o the changes in the patchset you posted):

diff --git a/drivers/gpu/drm/drm_probe_helper.c b/drivers/gpu/drm/drm_probe_helper.c index 0e5eadc6d44d..a515b78f839e 100644 --- a/drivers/gpu/drm/drm_probe_helper.c +++ b/drivers/gpu/drm/drm_probe_helper.c @@ -250,7 +250,7 @@ void drm_kms_helper_poll_enable(struct drm_device *dev) unsigned long delay = DRM_OUTPUT_POLL_PERIOD;

if (drm_WARN_ON_ONCE(dev, !dev->mode_config.poll_enabled) || - !drm_kms_helper_poll || dev->mode_config.poll_running) + !drm_kms_helper_poll) return;

drm_connector_list_iter_begin(dev, &conn_iter);

If this doesn't resolve the issue, I think we need to figure out the actual root cause, for that could you please open at a ticket at

https://gitlab.freedesktop.org/drm/i915/kernel/-/issues/new

attaching a dmesg log booting v6.1.147 and if possible also the latest drm-tip kernel with the drm.debug=0xe kernel parameter?

Thanks, Imre

On Wed, Jul 30, 2025 at 07:11:01PM +0300, Nicusor Huhulea wrote:

Hello maintainers,

This series addresses a defect observed on certain hardware platforms using Linux kernel 6.1.147 with the i915 driver. The issue concerns hot plug detection (HPD) logic, leading to unreliable or missed detection events on affected hardware. This is happening on some specific devices.

### Background

Issue: On Simatic IPC227E, we observed unreliable or missing hot plug detection events, while on Simatic IPC227G (otherwise similar platform), expected hot plug behavior was maintained. Affected kernel: This patch series is intended for the Linux 6.1.y stable tree only (tested on 6.1.147) Most of the tests were conducted on 6.1.147 (manual/standalone kernel build, CIP/Isar context). Root cause analysis: I do not have access to hardware signal traces or scope data to conclusively prove the root cause at electrical level. My understanding is based on observed driver behavior and logs. Therefore my assumption as to the real cause is that on IPC227G, HPD IRQ storms are apparently not occurring, so the standard HPD IRQ-based detection works as expected. On IPC227E, frequent HPD interrupts trigger the i915 driver’s storm detection logic, causing it to switch to polling mode. Therefore polling does not resume correctly, leading to the hotplug issue this series addresses. Device IPC227E's behavior triggers this kernel edge case, likely due to slight variations in signal integrity, electrical margins, or internal component timing. Device IPC227G, functions as expected, possibly due to cleaner electrical signaling or more optimal timing characteristics, thus avoiding the triggering condition. Conclusion: This points to a hardware-software interaction where kernel code assumes nicer signaling or margins than IPC227E is able to provide, exposing logic gaps not visible on more robust hardware.

### Patches

Patches 1-4: - Partial backports of upstream commits; only the relevant logic or fixes are applied, with other code omitted due to downstream divergence. - Applied minimal merging without exhaustive backport of all intermediate upstream changes. Patch 5: - Contains cherry-picked logic plus context/compatibility amendments as needed. Ensures that the driver builds. - Together these fixes greatly improve reliability of hotplug detection on both devices, with no regression detected in our setups.

Thank you for your review, Nicusor Huhulea

This patch series contains the following changes:

Dmitry Baryshkov (2): drm/probe_helper: extract two helper functions drm/probe-helper: enable and disable HPD on connectors

Imre Deak (2): drm/i915: Fix HPD polling, reenabling the output poll work as needed drm: Add an HPD poll helper to reschedule the poll work

Nicusor Huhulea (1): drm/i915: fixes for i915 Hot Plug Detection and build/runtime issues

drivers/gpu/drm/drm_probe_helper.c | 127 ++++++++++++++----- drivers/gpu/drm/i915/display/intel_hotplug.c | 4 +- include/drm/drm_modeset_helper_vtables.h | 22 ++++ include/drm/drm_probe_helper.h | 1 + 4 files changed, 122 insertions(+), 32 deletions(-)

-- 2.39.2