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

[Alexandre Courbot]

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 <acour...@chromium.org>
Reviewed-by: Tomasz Figa <tf...@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