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

From: Anand Moon <linux.amoon@gmail.com>
To: Neil Armstrong <neil.armstrong@linaro.org>,
	Maarten Lankhorst <maarten.lankhorst@linux.intel.com>,
	Maxime Ripard <mripard@kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@gmail.com>, Simona Vetter <simona@ffwll.ch>,
	Kevin Hilman <khilman@baylibre.com>,
	Jerome Brunet <jbrunet@baylibre.com>,
	Martin Blumenstingl <martin.blumenstingl@googlemail.com>,
	Mauro Carvalho Chehab <mchehab@kernel.org>,
	Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
	dri-devel@lists.freedesktop.org (open list:DRM DRIVERS FOR
	AMLOGIC SOCS),
	linux-amlogic@lists.infradead.org (open list:DRM DRIVERS FOR
	AMLOGIC SOCS),
	linux-arm-kernel@lists.infradead.org (moderated list:ARM/Amlogic
	Meson SoC support), linux-kernel@vger.kernel.org (open list),
	linux-media@vger.kernel.org (open list:MESON VIDEO DECODER
	DRIVER FOR AMLOGIC SOCS),
	linux-staging@lists.linux.dev (open list:STAGING SUBSYSTEM)
Cc: Doruk Tan Ozturk <doruk@0sec.ai>,
	Nicolas Dufresne <nicolas@ndufresne.ca>
Subject: [PATCH v7 19/19] gpu: drm: meson: Fix DMA segment size limits and maximize allocation boundaries
Date: Mon, 13 Jul 2026 17:37:14 +0530	[thread overview]
Message-ID: <20260713120840.17427-20-linux.amoon@gmail.com> (raw)
In-Reply-To: <20260713120840.17427-1-linux.amoon@gmail.com>

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@ndufresne.ca>
Signed-off-by: Anand Moon <linux.amoon@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


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