Claude review: drm/i915/display: Error codes for async flip failures

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Patch Review

> +		drm_mode_atomic_add_error_msg(&state->base.error_code,
> +					      DRM_MODE_ATOMIC_INVALID_API_USAGE,
> +					      "[PLANE:%d:%s] pixel format %p4cc / 0x%llx modifier does not support async flip",
> +					      plane->base.base.id, plane->base.name,
> +					      &new_plane_state->hw.fb->format->format,
> +					      new_plane_state->hw.fb->modifier);

The `%p4cc` format specifier is a kernel printk extension. While `kvasprintf` (used internally) does support it, the resulting string is copied to userspace. The kernel %p extensions produce kernel-internal formatting that may change between kernel versions. Passing kernel-formatted strings to userspace as a stable API is fragile. Consider using a plain hex value instead.

The conversion is also incomplete. Only 3 out of many error cases in `intel_async_flip_check_uapi` and `intel_async_flip_check_hw` have been converted. For example, the "not active", "joiner disallowed", "no old or new framebuffer", "stride cannot change", "modifier cannot change", etc. cases all still use `drm_dbg_kms`. If the feature is to be useful, it should cover all error paths, not just a few.

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