linux-kernel - [PATCH 3/3] drm/etnaviv: use a 32 bit mask as coherent DMA mask

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Message-Id: <20210826121006.685257-4-michael@walle.cc>
Date:   Thu, 26 Aug 2021 14:10:06 +0200
From:   Michael Walle <michael@...le.cc>
To:     etnaviv@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org
Cc:     "Lukas F . Hartmann" <lukas@...re.com>,
        Marek Vasut <marek.vasut@...il.com>,
        Lucas Stach <l.stach@...gutronix.de>,
        Russell King <linux+etnaviv@...linux.org.uk>,
        Christian Gmeiner <christian.gmeiner@...il.com>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Michael Walle <michael@...le.cc>
Subject: [PATCH 3/3] drm/etnaviv: use a 32 bit mask as coherent DMA mask

The STLB and the first command buffer (which is used to set up the TLBs)
has a 32 bit size restriction in hardware. There seems to be no way to
specify addresses larger than 32 bit. Keep it simple and restict the
addresses to the lower 4 GiB range for all coherent DMA memory
allocations.

Signed-off-by: Michael Walle <michael@...le.cc>
---
 drivers/gpu/drm/etnaviv/etnaviv_drv.c | 19 +++++++++++++++++--
 1 file changed, 17 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/etnaviv/etnaviv_drv.c b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
index ff6425f6ebad..0b756ecb1bc2 100644
--- a/drivers/gpu/drm/etnaviv/etnaviv_drv.c
+++ b/drivers/gpu/drm/etnaviv/etnaviv_drv.c
@@ -613,8 +613,23 @@ static int etnaviv_pdev_probe(struct platform_device *pdev)
 			component_match_add(dev, &match, compare_str, names[i]);
 	}
 
-	pdev->dev.coherent_dma_mask = DMA_BIT_MASK(40);
-	pdev->dev.dma_mask = &pdev->dev.coherent_dma_mask;
+	/*
+	 * PTA and MTLB can have 40 bit base addresses, but
+	 * unfortunately, an entry in the MTLB can only point to a
+	 * 32 bit base address of a STLB. Moreover, to initialize the
+	 * MMU we need a command buffer with a 32 bit address because
+	 * without an MMU there is only an indentity mapping between
+	 * the internal 32 bit addresses and the bus addresses.
+	 *
+	 * To make things easy, we set the dma_coherent_mask to 32
+	 * bit to make sure we are allocating the command buffers and
+	 * TLBs in the lower 4 GiB address space.
+	 */
+	if (dma_set_mask(&pdev->dev, DMA_BIT_MASK(40)) ||
+	    dma_set_coherent_mask(&pdev->dev, DMA_BIT_MASK(32))) {
+		dev_dbg(&pdev->dev, "No suitable DMA available\n");
+		return -ENODEV;
+	}
 
 	/*
 	 * Apply the same DMA configuration to the virtual etnaviv
-- 
2.30.2