linux-kernel - [PATCH net-next v2 3/4] net: ipa: fix table alignment requirement

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Date:   Thu, 18 Mar 2021 08:51:40 -0500
From:   Alex Elder <elder@...aro.org>
To:     davem@...emloft.net, kuba@...nel.org
Cc:     f.fainelli@...il.com, bjorn.andersson@...aro.org,
        evgreen@...omium.org, cpratapa@...eaurora.org,
        subashab@...eaurora.org, elder@...nel.org, netdev@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: [PATCH net-next v2 3/4] net: ipa: fix table alignment requirement

We currently have a build-time check to ensure that the minimum DMA
allocation alignment satisfies the constraint that IPA filter and
route tables must point to rules that are 128-byte aligned.

But what's really important is that the actual allocated DMA memory
has that alignment, even if the minimum is smaller than that.

Remove the BUILD_BUG_ON() call checking against minimim DMA alignment
and instead verify at rutime that the allocated memory is properly
aligned.

Signed-off-by: Alex Elder <elder@...aro.org>
---
 drivers/net/ipa/ipa_table.c | 20 ++++++++++++--------
 1 file changed, 12 insertions(+), 8 deletions(-)

diff --git a/drivers/net/ipa/ipa_table.c b/drivers/net/ipa/ipa_table.c
index dd07fe9dd87a3..988f2c2886b95 100644
--- a/drivers/net/ipa/ipa_table.c
+++ b/drivers/net/ipa/ipa_table.c
@@ -118,14 +118,6 @@
 /* Check things that can be validated at build time. */
 static void ipa_table_validate_build(void)
 {
-	/* IPA hardware accesses memory 128 bytes at a time.  Addresses
-	 * referred to by entries in filter and route tables must be
-	 * aligned on 128-byte byte boundaries.  The only rule address
-	 * ever use is the "zero rule", and it's aligned at the base
-	 * of a coherent DMA allocation.
-	 */
-	BUILD_BUG_ON(ARCH_DMA_MINALIGN % IPA_TABLE_ALIGN);
-
 	/* Filter and route tables contain DMA addresses that refer
 	 * to filter or route rules.  But the size of a table entry
 	 * is 64 bits regardless of what the size of an AP DMA address
@@ -665,6 +657,18 @@ int ipa_table_init(struct ipa *ipa)
 	if (!virt)
 		return -ENOMEM;
 
+	/* We put the "zero rule" at the base of our table area.  The IPA
+	 * hardware requires rules to be aligned on a 128-byte boundary.
+	 * Make sure the allocation satisfies this constraint.
+	 */
+	if (addr % IPA_TABLE_ALIGN) {
+		dev_err(dev, "table address %pad not %u-byte aligned\n",
+			&addr, IPA_TABLE_ALIGN);
+		dma_free_coherent(dev, size, virt, addr);
+
+		return -ERANGE;
+	}
+
 	ipa->table_virt = virt;
 	ipa->table_addr = addr;
 
-- 
2.27.0