On 3/24/21 11:27 AM, David Laight wrote:
From: Alex Elder
Sent: 23 March 2021 01:05
It is possible for a 32 bit x86 build to use a 64 bit DMA address.
There are two remaining spots where the IPA driver does a modulo
operation to check alignment of a DMA address, and under certain
conditions this can lead to a build error on i386 (at least).
The alignment checks we're doing are for power-of-2 values, and this
means the lower 32 bits of the DMA address can be used. This ensures
both operands to the modulo operator are 32 bits wide.
Reported-by: Randy Dunlap <rdun...@infradead.org>
Signed-off-by: Alex Elder <el...@linaro.org>
---
drivers/net/ipa/gsi.c | 11 +++++++----
drivers/net/ipa/ipa_table.c | 9 ++++++---
2 files changed, 13 insertions(+), 7 deletions(-)
diff --git a/drivers/net/ipa/gsi.c b/drivers/net/ipa/gsi.c
index 7f3e338ca7a72..b6355827bf900 100644
--- a/drivers/net/ipa/gsi.c
+++ b/drivers/net/ipa/gsi.c
@@ -1436,15 +1436,18 @@ static void gsi_evt_ring_rx_update(struct gsi_evt_ring
*evt_ring, u32 index)
/* Initialize a ring, including allocating DMA memory for its entries */
static int gsi_ring_alloc(struct gsi *gsi, struct gsi_ring *ring, u32 count)
{
- size_t size = count * GSI_RING_ELEMENT_SIZE;
+ u32 size = count * GSI_RING_ELEMENT_SIZE;
struct device *dev = gsi->dev;
dma_addr_t addr;
- /* Hardware requires a 2^n ring size, with alignment equal to size */
+ /* Hardware requires a 2^n ring size, with alignment equal to size.
+ * The size is a power of 2, so we can check alignment using just
+ * the bottom 32 bits for a DMA address of any size.
+ */
ring->virt = dma_alloc_coherent(dev, size, &addr, GFP_KERNEL);
Doesn't dma_alloc_coherent() guarantee that alignment?
I doubt anywhere else checks?
I normally wouldn't check something like this if it
weren't guaranteed. I'm not sure why I did it here.
I see it's "guaranteed to be aligned to the smallest
PAGE_SIZE order which is greater than or equal to
the requested size." So I think the answer to your
question is "yes, it does guarantee that."
I'll make a note to remove this check in a future
patch, and will credit you with the suggestion.
Thanks.
-Alex
David
-
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