linux-kernel - [PATCH v2 3/4] dma-pool: Introduce dma_guess

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Date:   Tue, 14 Jul 2020 14:39:27 +0200
From:   Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
To:     hch@....de, linux-kernel@...r.kernel.org,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Robin Murphy <robin.murphy@....com>
Cc:     linux-rpi-kernel@...ts.infradead.org, jeremy.linton@....com,
        Nicolas Saenz Julienne <nsaenzjulienne@...e.de>,
        iommu@...ts.linux-foundation.org
Subject: [PATCH v2 3/4] dma-pool: Introduce dma_guess_pool()

dma-pool's dev_to_pool() creates the false impression that there is a
way to grantee a mapping between a device's DMA constraints and an
atomic pool. It tuns out it's just a guess, and the device might need to
use an atomic pool containing memory from a 'safer' (or lower) memory
zone.

To help mitigate this, introduce dma_guess_pool() which can be fed a
device's DMA constraints and atomic pools already known to be faulty, in
order for it to provide an better guess on which pool to use.

Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@...e.de>
---
 kernel/dma/pool.c | 26 +++++++++++++++++++++++---
 1 file changed, 23 insertions(+), 3 deletions(-)

diff --git a/kernel/dma/pool.c b/kernel/dma/pool.c
index 318035e093fb..5b9eaa2b498d 100644
--- a/kernel/dma/pool.c
+++ b/kernel/dma/pool.c
@@ -203,7 +203,7 @@ static int __init dma_atomic_pool_init(void)
 }
 postcore_initcall(dma_atomic_pool_init);
 
-static inline struct gen_pool *dev_to_pool(struct device *dev)
+static inline struct gen_pool *dma_guess_pool_from_device(struct device *dev)
 {
 	u64 phys_mask;
 	gfp_t gfp;
@@ -217,10 +217,30 @@ static inline struct gen_pool *dev_to_pool(struct device *dev)
 	return atomic_pool_kernel;
 }
 
+static inline struct gen_pool *dma_get_safer_pool(struct gen_pool *bad_pool)
+{
+	if (bad_pool == atomic_pool_kernel)
+		return atomic_pool_dma32 ? : atomic_pool_dma;
+
+	if (bad_pool == atomic_pool_dma32)
+		return atomic_pool_dma;
+
+	return NULL;
+}
+
+static inline struct gen_pool *dma_guess_pool(struct device *dev,
+					      struct gen_pool *bad_pool)
+{
+	if (bad_pool)
+		return dma_get_safer_pool(bad_pool);
+
+	return dma_guess_pool_from_device(dev);
+}
+
 void *dma_alloc_from_pool(struct device *dev, size_t size,
 			  struct page **ret_page, gfp_t flags)
 {
-	struct gen_pool *pool = dev_to_pool(dev);
+	struct gen_pool *pool = dma_guess_pool(dev, NULL);
 	unsigned long val;
 	void *ptr = NULL;
 
@@ -249,7 +269,7 @@ void *dma_alloc_from_pool(struct device *dev, size_t size,
 
 bool dma_free_from_pool(struct device *dev, void *start, size_t size)
 {
-	struct gen_pool *pool = dev_to_pool(dev);
+	struct gen_pool *pool = dma_guess_pool(dev, NULL);
 
 	if (!pool || !gen_pool_has_addr(pool, (unsigned long)start, size))
 		return false;
-- 
2.27.0