linux-kernel - [PATCH v4 1/3] drm/nouveau: set streaming DMA mask early

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Message-Id: <1474893160-12321-2-git-send-email-ard.biesheuvel@linaro.org>
Date:   Mon, 26 Sep 2016 05:32:38 -0700
From:   Ard Biesheuvel <ard.biesheuvel@...aro.org>
To:     linux-kernel@...r.kernel.org, bskeggs@...hat.com, airlied@...ux.ie,
        dri-devel@...ts.freedesktop.org, nouveau@...ts.freedesktop.org
Cc:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
Subject: [PATCH v4 1/3] drm/nouveau: set streaming DMA mask early

Some subdevices (i.e., fb/nv50.c and fb/gf100.c) map a scratch page using
dma_map_page() way before the TTM layer has had a chance to set the DMA
mask. This may prevent the driver from loading at all on platforms whose
system memory is not covered by the default DMA mask of 32-bit (i.e., when
all RAM is above 4 GB).

So set a preliminary DMA mask right after constructing the PCI device, and
base it on the .dma_bits member of the MMU subdevice, which is what the TTM
layer will base the DMA mask on as well.

Signed-off-by: Ard Biesheuvel <ard.biesheuvel@...aro.org>
---
 drivers/gpu/drm/nouveau/nouveau_drm.c | 11 +++++++++++
 1 file changed, 11 insertions(+)

diff --git a/drivers/gpu/drm/nouveau/nouveau_drm.c b/drivers/gpu/drm/nouveau/nouveau_drm.c
index 652ab111dd74..e61e9a0adb51 100644
--- a/drivers/gpu/drm/nouveau/nouveau_drm.c
+++ b/drivers/gpu/drm/nouveau/nouveau_drm.c
@@ -361,6 +361,17 @@ static int nouveau_drm_probe(struct pci_dev *pdev,
 
 	pci_set_master(pdev);
 
+	/*
+	 * Set a preliminary DMA mask based on the .dma_bits member of the
+	 * MMU subdevice. This allows other subdevices to create DMA mappings
+	 * in their init() function, which are called before the TTM layer sets
+	 * the DMA mask definitively.
+	 * This is necessary for platforms where the default DMA mask of 32
+	 * does not cover any system memory, i.e., when all RAM is > 4 GB.
+	 */
+	dma_set_mask_and_coherent(device->dev,
+				  DMA_BIT_MASK(device->mmu->dma_bits));
+
 	ret = drm_get_pci_dev(pdev, pent, &driver_pci);
 	if (ret) {
 		nvkm_device_del(&device);
-- 
2.7.4