linux-kernel - [PATCH v3 2/7] OF: Simplify DMA range calculations

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Date: Fri,  9 Feb 2024 16:49:59 +0000
From: Robin Murphy <robin.murphy@....com>
To: 
Cc: Vineet Gupta <vgupta@...nel.org>,
	Russell King <linux@...linux.org.uk>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will@...nel.org>,
	Huacai Chen <chenhuacai@...nel.org>,
	WANG Xuerui <kernel@...0n.name>,
	Thomas Bogendoerfer <tsbogend@...ha.franken.de>,
	Paul Walmsley <paul.walmsley@...ive.com>,
	Palmer Dabbelt <palmer@...belt.com>,
	Albert Ou <aou@...s.berkeley.edu>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Hanjun Guo <guohanjun@...wei.com>,
	Sudeep Holla <sudeep.holla@....com>,
	"K. Y. Srinivasan" <kys@...rosoft.com>,
	Haiyang Zhang <haiyangz@...rosoft.com>,
	Wei Liu <wei.liu@...nel.org>,
	Dexuan Cui <decui@...rosoft.com>,
	Suravee Suthikulpanit <suravee.suthikulpanit@....com>,
	David Woodhouse <dwmw2@...radead.org>,
	Lu Baolu <baolu.lu@...ux.intel.com>,
	Niklas Schnelle <schnelle@...ux.ibm.com>,
	Matthew Rosato <mjrosato@...ux.ibm.com>,
	Gerald Schaefer <gerald.schaefer@...ux.ibm.com>,
	Jean-Philippe Brucker <jean-philippe@...aro.org>,
	Rob Herring <robh+dt@...nel.org>,
	Frank Rowand <frowand.list@...il.com>,
	Marek Szyprowski <m.szyprowski@...sung.com>,
	Jason Gunthorpe <jgg@...pe.ca>,
	linux-kernel@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org,
	linux-acpi@...r.kernel.org,
	iommu@...ts.linux.dev,
	devicetree@...r.kernel.org,
	Rob Herring <robh@...nel.org>,
	Jason Gunthorpe <jgg@...dia.com>
Subject: [PATCH v3 2/7] OF: Simplify DMA range calculations

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).

Acked-by: Rob Herring <robh@...nel.org>
Reviewed-by: Jason Gunthorpe <jgg@...dia.com>
Signed-off-by: Robin Murphy <robin.murphy@....com>
---
 drivers/of/device.c | 19 ++++++++-----------
 1 file changed, 8 insertions(+), 11 deletions(-)

diff --git a/drivers/of/device.c b/drivers/of/device.c
index a988bee2ee5a..841ccd3a19d1 100644
--- a/drivers/of/device.c
+++ b/drivers/of/device.c
@@ -96,7 +96,7 @@ 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 iommu_ret;
 	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;
@@ -185,7 +182,7 @@ int of_dma_configure_id(struct device *dev, struct device_node *np,
 	} else
 		dev_dbg(dev, "device is behind an iommu\n");
 
-	arch_setup_dma_ops(dev, dma_start, size, coherent);
+	arch_setup_dma_ops(dev, dma_start, end - dma_start + 1, coherent);
 
 	if (iommu_ret)
 		of_dma_set_restricted_buffer(dev, np);
-- 
2.39.2.101.g768bb238c484.dirty