Re: [PATCH 6.1.y-cip 0/5] drm/i915: fixes for i915 Hot Plug Detection and build/runtime issues

[Jan Kiszka <jan.kiszka@siemens.com>]

On 23.07.25 14:54, Nicusor Huhulea wrote:
> Hello maintainers,
> 
> This series addresses a defect observed on certain hardware platforms using Linux kernel 6.1.127 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:
>     Most of the tests were conducted on 6.1.127 (manual/standalone kernel build, CIP/Isar context). But it also happens on 6.1.145-cip44
> Root cause analysis:
>     Through testing and diagnostics, it appears that the HPD finite state machine or polling logic in kernel 6.1.127 is marginal for this edge case. Device IPC227E's behavior triggers
>     this kernel edge case, likely due to slight variations in signal integrity, electrical margins, or internal component timing.
>     Simatic IPC227G, functions as expected, possibly due to cleaner electrical signaling or more optimal timing characteristics, thus avoiding the triggering condition.
> Summary:
>     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.
> Patch 5:
>     - Additional modifications to ensure the driver builds and resolves run-time issues
>     - Contains cherry-picked logic plus context/compatibility amendments as needed.
>     - Together these fixes greatly improve reliability of hotplug detection on both devices, with no regression detected in our setups.

What is this series targeting, regular stable 6.1 or 6.1-cip only? If
the latter, why only cip? 6.1 stable is still alive, and this introduces
itself as fix.

Jan

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