[PATCH v2 2/2] drm/mediatek: set DMA max segment size

[Alexandre Courbot <acourbot@chromium.org>]

This driver requires imported PRIME buffers to appear contiguously in
its IO address space. Make sure this is the case by setting the maximum
DMA segment size to a more suitable value than the default 64KB.

Signed-off-by: Alexandre Courbot <acourbot@chromium.org>
Reviewed-by: Tomasz Figa <tfiga@chromium.org>
---
 drivers/gpu/drm/mediatek/mtk_drm_drv.c | 35 ++++++++++++++++++++++++--
 drivers/gpu/drm/mediatek/mtk_drm_drv.h |  2 ++
 2 files changed, 35 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
index 8b18a00a58c7..c021d4c8324f 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
+++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
@@ -213,6 +213,7 @@ static int mtk_drm_kms_init(struct drm_device *drm)
 	struct mtk_drm_private *private = drm->dev_private;
 	struct platform_device *pdev;
 	struct device_node *np;
+	struct device *dma_dev;
 	int ret;
 
 	if (!iommu_present(&platform_bus_type))
@@ -275,7 +276,29 @@ static int mtk_drm_kms_init(struct drm_device *drm)
 		goto err_component_unbind;
 	}
 
-	private->dma_dev = &pdev->dev;
+	dma_dev = &pdev->dev;
+	private->dma_dev = dma_dev;
+
+	/*
+	 * Configure the DMA segment size to make sure we get contiguous IOVA
+	 * when importing PRIME buffers.
+	 */
+	if (!dma_dev->dma_parms) {
+		private->dma_parms_allocated = true;
+		dma_dev->dma_parms =
+			devm_kzalloc(drm->dev, sizeof(*dma_dev->dma_parms),
+				     GFP_KERNEL);
+	}
+	if (!dma_dev->dma_parms) {
+		ret = -ENOMEM;
+		goto err_component_unbind;
+	}
+
+	ret = dma_set_max_seg_size(dma_dev, (unsigned int)DMA_BIT_MASK(32));
+	if (ret) {
+		dev_err(dma_dev, "Failed to set DMA segment size\n");
+		goto err_unset_dma_parms;
+	}
 
 	/*
 	 * We don't use the drm_irq_install() helpers provided by the DRM
@@ -285,13 +308,16 @@ static int mtk_drm_kms_init(struct drm_device *drm)
 	drm->irq_enabled = true;
 	ret = drm_vblank_init(drm, MAX_CRTC);
 	if (ret < 0)
-		goto err_component_unbind;
+		goto err_unset_dma_parms;
 
 	drm_kms_helper_poll_init(drm);
 	drm_mode_config_reset(drm);
 
 	return 0;
 
+err_unset_dma_parms:
+	if (private->dma_parms_allocated)
+		dma_dev->dma_parms = NULL;
 err_component_unbind:
 	component_unbind_all(drm->dev, drm);
 err_config_cleanup:
@@ -302,9 +328,14 @@ static int mtk_drm_kms_init(struct drm_device *drm)
 
 static void mtk_drm_kms_deinit(struct drm_device *drm)
 {
+	struct mtk_drm_private *private = drm->dev_private;
+
 	drm_kms_helper_poll_fini(drm);
 	drm_atomic_helper_shutdown(drm);
 
+	if (private->dma_parms_allocated)
+		private->dma_dev->dma_parms = NULL;
+
 	component_unbind_all(drm->dev, drm);
 	drm_mode_config_cleanup(drm);
 }
diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.h b/drivers/gpu/drm/mediatek/mtk_drm_drv.h
index 598ff3e70446..e03fea12ff59 100644
--- a/drivers/gpu/drm/mediatek/mtk_drm_drv.h
+++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.h
@@ -51,6 +51,8 @@ struct mtk_drm_private {
 	} commit;
 
 	struct drm_atomic_state *suspend_state;
+
+	bool dma_parms_allocated;
 };
 
 extern struct platform_driver mtk_ddp_driver;
-- 
2.22.0.709.g102302147b-goog