net: ipa: DMA addresses are nicely aligned

A recent patch avoided doing 64-bit modulo operations by checking
the alignment of some DMA allocations using only the lower 32 bits
of the address.

David Laight pointed out (after the fix was committed) that DMA
allocations might already satisfy the alignment requirements.  And
he was right.

Remove the alignment checks that occur after DMA allocation requests,
and update comments to explain why the constraint is satisfied.  The
only place IPA_TABLE_ALIGN was used was to check the alignment; it is
therefore no longer needed, so get rid of it.

Add comments where GSI_RING_ELEMENT_SIZE and the tre_count and
event_count channel data fields are defined to make explicit they
are required to be powers of 2.

Revise a comment in gsi_trans_pool_init_dma(), taking into account
that dma_alloc_coherent() guarantees its result is aligned to a page
size (or order thereof).

Don't bother printing an error if a DMA allocation fails.

Suggested-by: David Laight <David.Laight@ACULAB.COM>
Signed-off-by: Alex Elder <elder@linaro.org>
Signed-off-by: David S. Miller <davem@davemloft.net>

1 files changed, 6 insertions, 18 deletions

diff --git a/drivers/net/ipa/ipa_table.c b/drivers/net/ipa/ipa_table.c
index 4236a50ff03a..d9538661755f 100644
--- a/drivers/net/ipa/ipa_table.c
+++ b/drivers/net/ipa/ipa_table.c
@@ -96,9 +96,6 @@
  *                 ----------------------
  */
 
-/* IPA hardware constrains filter and route tables alignment */
-#define IPA_TABLE_ALIGN			128	/* Minimum table alignment */
-
 /* Assignment of route table entries to the modem and AP */
 #define IPA_ROUTE_MODEM_MIN		0
 #define IPA_ROUTE_MODEM_COUNT		8
@@ -652,26 +649,17 @@ int ipa_table_init(struct ipa *ipa)
 
 	ipa_table_validate_build();
 
+	/* The IPA hardware requires route and filter table rules to be
+	 * aligned on a 128-byte boundary.  We put the "zero rule" at the
+	 * base of the table area allocated here.  The DMA address returned
+	 * by dma_alloc_coherent() is guaranteed to be a power-of-2 number
+	 * of pages, which satisfies the rule alignment requirement.
+	 */
 	size = IPA_ZERO_RULE_SIZE + (1 + count) * IPA_TABLE_ENTRY_SIZE;
 	virt = dma_alloc_coherent(dev, size, &addr, GFP_KERNEL);
 	if (!virt)
 		return -ENOMEM;
 
-	/* We put the "zero rule" at the base of our table area.  The IPA
-	 * hardware requires route and filter table rules to be aligned
-	 * on a 128-byte boundary.  As long as the alignment constraint
-	 * is a power of 2, we can check alignment using just the bottom
-	 * 32 bits for a DMA address of any size.
-	 */
-	BUILD_BUG_ON(!is_power_of_2(IPA_TABLE_ALIGN));
-	if (lower_32_bits(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;