forked from marfrit/libva-v4l2-request-fourier
test0r
597e896594
The hantro stateless decoder derives the CAPTURE format from the SPS attached to the per-request OUTPUT controls. Calling VIDIOC_S_FMT on the CAPTURE queue at vaCreateSurfaces2 time can leave the driver's vb2 state in an inconsistent configuration where the queue accepts buffers and DQBUF returns successfully but the kernel never actually writes decoded pixels into them. Cross-reference: GStreamer's gst-plugins-bad/sys/v4l2codecs/ gstv4l2decoder.c only calls VIDIOC_G_FMT on the CAPTURE side (via gst_v4l2_decoder_negotiate_src_format and friends). The same code path produces correctly-decoded NV12 frames on the same RK3568 hantro-vpu where libva-v4l2-request-with-S_FMT emits flat-green zeroed CAPTURE buffers. The v4l2_get_format() call immediately after this block already gives us the bytesperline / sizes the driver chose; nothing else in this file consumed the explicit S_FMT side-effects. Empirical hypothesis test for the lingering "kernel decodes without errors but emits zeroed CAPTURE" bug. If post-patch output shows actual picture content, this confirms the diagnosis: explicit CAPTURE format mutation breaks hantro's internal state. If output remains flat-green, the bug is elsewhere and we resume hex-dump-grade instrumentation. Signed-off-by: Markus Fritsche <fritsche.markus@gmail.com>