[PATCH v7 19/19] gpu: drm: meson: Fix DMA segment size limits and maximize allocation boundaries

[Anand Moon]

When importing DMABUFs exported by the Amlogic video decoder driver
(meson_vdec) for hardware-accelerated rendering paths, the DMA core
subsystem throws constraint validation warnings. This occurs because the
display controller master device lacks explicit DMA layout configuration,
causing it to fall back to a default 64KB maximum segment size limit.

Address these architectural constraints during the master bind sequence:

1. Initialize and validate a 32-bit coherent DMA allocation window by
   invoking dma_set_mask_and_coherent() with a DMA_BIT_MASK(32) argument.
2. Maximize the contiguous scatter-gather allocation segment boundary
   check constraint to UINT_MAX using the dma_set_max_seg_size() helper.

This guarantees that large video bitstream frame buffers can be imported
and scanned out across sub-driver domains without triggering allocation
warnings or page boundary splits.

Cc: Nicolas Dufresne <nicolas at ndufresne.ca>
Signed-off-by: Anand Moon <linux.amoon at gmail.com>
---
 drivers/gpu/drm/meson/meson_drv.c | 6 ++++++
 1 file changed, 6 insertions(+)

diff --git a/drivers/gpu/drm/meson/meson_drv.c b/drivers/gpu/drm/meson/meson_drv.c
index 49ff9f1f16d32..899e70bca4ce2 100644
--- a/drivers/gpu/drm/meson/meson_drv.c
+++ b/drivers/gpu/drm/meson/meson_drv.c
@@ -202,6 +202,12 @@ static int meson_drv_bind_master(struct device *dev, bool has_components)
 	if (IS_ERR(drm))
 		return PTR_ERR(drm);
 
+	ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
+	if (ret)
+		goto free_drm;
+
+	dma_set_max_seg_size(dev, UINT_MAX);
+
 	priv = devm_kzalloc(dev, sizeof(*priv), GFP_KERNEL);
 	if (!priv) {
 		ret = -ENOMEM;
-- 
2.50.1