[PATCH 1/2] of: Fix DMA mask generation

[Robin Murphy]

Historically, DMA masks have suffered some ambiguity between whether
they represent the range of physical memory a device can access, or the
address bits a device is capable of driving, particularly since on many
platforms the two are equivalent. Whilst there are some stragglers left
(dma_max_pfn(), I'm looking at you...), the majority of DMA code has
been cleaned up to follow the latter definition, not least since it is
the only one which makes sense once IOMMUs are involved.

In this respect, of_dma_configure() has always done the wrong thing in
how it generates initial masks based on "dma-ranges". Although rounding
down did not affect the TI Keystone platform where dma_addr + size is
already a power of two, in any other case it results in a mask which is
at best unnecessarily constrained and at worst unusable.

BCM2837 illustrates the problem nicely, where we have a DMA base of 3GB
and a size of 1GB - 16MB, giving dma_addr + size = 0xff000000 and a
resultant mask of 0x7fffffff, which is then insufficient to even cover
the necessary offset, effectively making all DMA addresses out-of-range.
This has been hidden until now (mostly because we don't yet prevent
drivers from simply overwriting this initial mask later upon probe), but
due to recent changes elsewhere now shows up as USB being broken on
Raspberry Pi 3.

Make it right by rounding up instead of down, such that the mask
correctly correctly describes all possisble bits the device needs to
emit.

Fixes: 9a6d7298b083 ("of: Calculate device DMA masks based on DT dma-range size")
Reported-by: Stefan Wahren <stefan.wahren at i2se.com>
Reported-by: Andreas Färber <afaerber at suse.de>
Reported-by: Hans Verkuil <hverkuil at xs4all.nl>
Signed-off-by: Robin Murphy <robin.murphy at arm.com>
---

Either of these patches alone should be sufficient to un-break RPi3,
and they apply independently, so I'm quite happy for one to go in as a
fix now and the other to wait for 4.14.

Robin.

 drivers/of/device.c | 8 ++++----
 1 file changed, 4 insertions(+), 4 deletions(-)

diff --git a/drivers/of/device.c b/drivers/of/device.c
index 28c38c756f92..e0a28ea341fe 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -89,6 +89,7 @@ int of_dma_configure(struct device *dev, struct device_node *np)
 	bool coherent;
 	unsigned long offset;
 	const struct iommu_ops *iommu;
+	u64 mask;
 
 	/*
 	 * Set default coherent_dma_mask to 32 bit.  Drivers are expected to
@@ -134,10 +135,9 @@ int of_dma_configure(struct device *dev, struct device_node *np)
 	 * Limit coherent and dma mask based on size and default mask
 	 * set by the driver.
 	 */
-	dev->coherent_dma_mask = min(dev->coherent_dma_mask,
-				     DMA_BIT_MASK(ilog2(dma_addr + size)));
-	*dev->dma_mask = min((*dev->dma_mask),
-			     DMA_BIT_MASK(ilog2(dma_addr + size)));
+	mask = DMA_BIT_MASK(ilog2(dma_addr + size - 1) + 1);
+	dev->coherent_dma_mask &= mask;
+	*dev->dma_mask &= mask;
 
 	coherent = of_dma_is_coherent(np);
 	dev_dbg(dev, "device is%sdma coherent\n",
-- 
2.13.4.dirty