mpv-fourier: iter1 patch — explicit DMA_BUF_IOCTL_SYNC on import fds

Workaround for the dmabuf-wayland green-frames bug
(marfrit/dmabuf-modifier-triage#1). iter1 phase 2 source-read of
KWin 6.6.4 + Mesa 26.0.6 ruled out the original H1/H2 hypotheses
(panfrost offset handling and KWin wl_dmabuf import are clean) and
matched the green tone to BT.601 limited-range YUV(0,0,0) -> RGB(0,
135, 0). Conclusion: panfrost reads zero-fill memory despite hantro
having written real data — a cache-coherency / synchronization gap.

V4L2 doesn't attach implicit fences (dma_resv) to CAPTURE buffers
on VIDIOC_DQBUF; this gap is the same one our vb2_dma_resv RFC v2
addresses upstream. The userspace workaround is to issue
DMA_BUF_IOCTL_SYNC(SYNC_START|SYNC_RW) + SYNC_END(SYNC_RW) on each
EXPBUF fd before submitting to the compositor — invokes the producer
driver's begin_cpu_access / end_cpu_access path, which on most ARM
SoCs flushes write buffers and synchronizes coherent memory.

Patch covers BOTH vaapi_dmabuf_importer (the path our test exercises
via `mpv --hwdec=vaapi`) and drmprime_dmabuf_importer (for symmetry
when used via `--hwdec=drmprime`).

If this works, ship it; if it doesn't, hypothesis space narrows
further to GPU-side cache invalidation in panfrost's kernel-mode
dma_buf import path (H7).

pkgrel 8 -> 9. Patch sha256
6c929bea7636b8d81b63a1275ba1d8a471fe2f249fc23509043ace6cf9b076a7.

arch/mpv-fourier/PKGBUILD

@@ -23,8 +23,8 @@ pkgname=mpv-fourier
 _upstreampkg=mpv
 epoch=1
 pkgver=0.41.0
-pkgrel=8
-pkgdesc='mpv with fourier-umbrella patches (vo_dmabuf_wayland plane-semantics fix slot)'
+pkgrel=9
+pkgdesc='mpv with fourier-umbrella patches (vo_dmabuf_wayland explicit cache-sync workaround)'
 arch=('aarch64')
 url='https://mpv.io/'
 license=('GPL-2.0-or-later AND LGPL-2.1-or-later')
@@ -49,21 +49,21 @@ options=('!emptydirs')
 
 source=(
     "${_upstreampkg}-${pkgver}.tar.gz::https://github.com/mpv-player/${_upstreampkg}/archive/v${pkgver}/${_upstreampkg}-${pkgver}.tar.gz"
+    '0001-vo_dmabuf_wayland-explicit-cache-sync-on-import-fd.patch'
 )
 sha256sums=(
     'ee21092a5ee427353392360929dc64645c54479aefdb5babc5cfbb5fad626209'
+    '6c929bea7636b8d81b63a1275ba1d8a471fe2f249fc23509043ace6cf9b076a7'
 )
 
 prepare() {
     cd "${_upstreampkg}-${pkgver}"
 
-    # Patch slot — iter1 of dmabuf-modifier-triage will produce the actual
-    # vo_dmabuf_wayland.c plane-semantics fix and add it as 0001-... here.
-    # When the patch lands, add it to source=() above + sha256sums=() and
-    # uncomment the patch -p1 below.
-    #
-    # patch -p1 < "${srcdir}/0001-vo_dmabuf_wayland-plane-semantics.patch"
-    :
+    # iter1 of dmabuf-modifier-triage — explicit DMA_BUF_IOCTL_SYNC on import
+    # fds in vaapi_dmabuf_importer + drmprime_dmabuf_importer. Workaround for
+    # missing implicit-fence on V4L2 stateless CAPTURE buffers; root cause is
+    # being addressed upstream via the vb2_dma_resv RFC.
+    patch -p1 < "${srcdir}/0001-vo_dmabuf_wayland-explicit-cache-sync-on-import-fd.patch"
 }
 
 build() {