diff mbox series

[2/7] OF: Simplify DMA range calculations

Message ID 73becf4a75f15662b2dda5fba7cfeacdf3d866f8.1701268753.git.robin.murphy@arm.com (mailing list archive)
State New, archived
Headers show
Series dma-mapping: Clean up arch_setup_dma_ops() | expand

Commit Message

Robin Murphy Nov. 29, 2023, 5:42 p.m. UTC
Juggling start, end, and size values for a range is somewhat redundant
and a little hard to follow. Consolidate down to just using inclusive
start and end, which saves us worrying about size overflows for full
64-bit ranges (note that passing a potentially-overflowed value through
to arch_setup_dma_ops() is benign for all current implementations, and
this is working towards removing that anyway).

Signed-off-by: Robin Murphy <robin.murphy@arm.com>
---
 drivers/of/device.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

Comments

Jason Gunthorpe Nov. 30, 2023, 12:46 a.m. UTC | #1
On Wed, Nov 29, 2023 at 05:42:59PM +0000, Robin Murphy wrote:
> Juggling start, end, and size values for a range is somewhat redundant
> and a little hard to follow. Consolidate down to just using inclusive
> start and end, which saves us worrying about size overflows for full
> 64-bit ranges (note that passing a potentially-overflowed value through
> to arch_setup_dma_ops() is benign for all current implementations, and
> this is working towards removing that anyway).

In iommu code I've been trying to use consistent language with other
parts of the kernel like interval tree and maple tree:

 * In this file the term 'last' indicates an inclusive and closed interval, eg
 * [0,0] refers to a single PFN. 'end' means an open range, eg [0,0) refers to
 * no PFNs.

Here I think you've swapped end to mean last?

Regardless the change looks correct

Reviewed-by: Jason Gunthorpe <jgg@nvidia.com>

Jason
Rob Herring Nov. 30, 2023, 2:56 p.m. UTC | #2
On Wed, Nov 29, 2023 at 11:43 AM Robin Murphy <robin.murphy@arm.com> wrote:
>
> Juggling start, end, and size values for a range is somewhat redundant
> and a little hard to follow. Consolidate down to just using inclusive
> start and end, which saves us worrying about size overflows for full
> 64-bit ranges (note that passing a potentially-overflowed value through
> to arch_setup_dma_ops() is benign for all current implementations, and
> this is working towards removing that anyway).
>
> Signed-off-by: Robin Murphy <robin.murphy@arm.com>
> ---
>  drivers/of/device.c | 19 ++++++++-----------
>  1 file changed, 8 insertions(+), 11 deletions(-)

Acked-by: Rob Herring <robh@kernel.org>
diff mbox series

Patch

diff --git a/drivers/of/device.c b/drivers/of/device.c
index 526a42cdf66e..51062a831970 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -97,7 +97,7 @@  int of_dma_configure_id(struct device *dev, struct device_node *np,
 	const struct bus_dma_region *map = NULL;
 	struct device_node *bus_np;
 	u64 dma_start = 0;
-	u64 mask, end, size = 0;
+	u64 mask, end = 0;
 	bool coherent;
 	int ret;
 
@@ -118,17 +118,15 @@  int of_dma_configure_id(struct device *dev, struct device_node *np,
 			return ret == -ENODEV ? 0 : ret;
 	} else {
 		const struct bus_dma_region *r = map;
-		u64 dma_end = 0;
 
 		/* Determine the overall bounds of all DMA regions */
 		for (dma_start = ~0; r->size; r++) {
 			/* Take lower and upper limits */
 			if (r->dma_start < dma_start)
 				dma_start = r->dma_start;
-			if (r->dma_start + r->size > dma_end)
-				dma_end = r->dma_start + r->size;
+			if (r->dma_start + r->size > end)
+				end = r->dma_start + r->size;
 		}
-		size = dma_end - dma_start;
 	}
 
 	/*
@@ -142,16 +140,15 @@  int of_dma_configure_id(struct device *dev, struct device_node *np,
 		dev->dma_mask = &dev->coherent_dma_mask;
 	}
 
-	if (!size && dev->coherent_dma_mask)
-		size = max(dev->coherent_dma_mask, dev->coherent_dma_mask + 1);
-	else if (!size)
-		size = 1ULL << 32;
+	if (!end && dev->coherent_dma_mask)
+		end = dev->coherent_dma_mask;
+	else if (!end)
+		end = (1ULL << 32) - 1;
 
 	/*
 	 * Limit coherent and dma mask based on size and default mask
 	 * set by the driver.
 	 */
-	end = dma_start + size - 1;
 	mask = DMA_BIT_MASK(ilog2(end) + 1);
 	dev->coherent_dma_mask &= mask;
 	*dev->dma_mask &= mask;
@@ -177,7 +174,7 @@  int of_dma_configure_id(struct device *dev, struct device_node *np,
 	dev_dbg(dev, "device is%sbehind an iommu\n",
 		iommu ? " " : " not ");
 
-	arch_setup_dma_ops(dev, dma_start, size, iommu, coherent);
+	arch_setup_dma_ops(dev, dma_start, end - dma_start + 1, iommu, coherent);
 
 	if (!iommu)
 		of_dma_set_restricted_buffer(dev, np);