[PATCH v7 16/19] media: meson: vdec: Configure DMA mask and segment size in probe

[Anand Moon]

The vdec probe routine does not set explicit DMA constraints, leaving the
driver completely dependent on platform bus default values. This lack of
explicit layout initialization can lead to allocation failures, restricted
address space mappings, or broken contiguous buffer handling on
architectures with restrictive DMA layers.

Address these platform constraints with the following changes during driver
initialization:
1. Enforce 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 allocation segment boundary constraint to
   UINT_MAX using the vb2_dma_contig_set_max_seg_size() configuration
   helper.

This guarantees that large, contiguous video frame allocation requests
work reliably and explicitly aligns the memory management paths with
standard Linux kernel DMA management paradigms.

Cc: Nicolas Dufresne <nicolas@xxxxxxxxxxxx>
Signed-off-by: Anand Moon <linux.amoon@xxxxxxxxx>
---
 drivers/staging/media/meson/vdec/vdec.c | 10 ++++++++++
 1 file changed, 10 insertions(+)

diff --git a/drivers/staging/media/meson/vdec/vdec.c b/drivers/staging/media/meson/vdec/vdec.c
index ac86a9c4febff..d33cbebc4453b 100644
--- a/drivers/staging/media/meson/vdec/vdec.c
+++ b/drivers/staging/media/meson/vdec/vdec.c
@@ -1186,6 +1186,16 @@ static int vdec_probe(struct platform_device *pdev)
 	if (IS_ERR(core->canvas))
 		return PTR_ERR(core->canvas);
 
+	/* Enforce strict 32-bit DMA limit to match hardware capabilities */
+	ret = dma_set_mask_and_coherent(dev, DMA_BIT_MASK(32));
+	if (ret)
+		return dev_err_probe(dev, ret, "Failed to set 32-bit DMA mask\n");
+
+	ret = vb2_dma_contig_set_max_seg_size(dev, UINT_MAX);
+	if (ret)
+		return dev_err_probe(dev, ret,
+				     "Failed to set DMA max segment size\n");
+
 	of_id = of_match_node(vdec_dt_match, dev->of_node);
 	core->platform = of_id->data;
 
-- 
2.50.1