Re: [PATCH] net: octeontx2: Make sure the buffer is 128 byte aligned

On Thu, Jan 21, 2021 at 5:26 PM Kevin Hao [off-list ref] wrote:

On Thu, Jan 21, 2021 at 09:53:08AM +0000, David Laight wrote:

quoted

From: Kevin Hao

quoted

Sent: 21 January 2021 07:09

The octeontx2 hardware needs the buffer to be 128 byte aligned.
But in the current implementation of napi_alloc_frag(), it can't
guarantee the return address is 128 byte aligned even the request size
is a multiple of 128 bytes, so we have to request an extra 128 bytes and
use the PTR_ALIGN() to make sure that the buffer is aligned correctly.

Fixes: 7a36e4918e30 ("octeontx2-pf: Use the napi_alloc_frag() to alloc the pool buffers")
Reported-by: Subbaraya Sundeep <sbhatta@marvell.com>
Signed-off-by: Kevin Hao <redacted>
---
 drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c | 3 ++-
 1 file changed, 2 insertions(+), 1 deletion(-)

diff --git a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c

b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
index bdfa2e293531..5ddedc3b754d 100644

--- a/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c
+++ b/drivers/net/ethernet/marvell/octeontx2/nic/otx2_common.c

@@ -488,10 +488,11 @@ dma_addr_t __otx2_alloc_rbuf(struct otx2_nic *pfvf, struct otx2_pool *pool)
    dma_addr_t iova;
    u8 *buf;

-   buf = napi_alloc_frag(pool->rbsize);
+   buf = napi_alloc_frag(pool->rbsize + OTX2_ALIGN);
    if (unlikely(!buf))
            return -ENOMEM;

+   buf = PTR_ALIGN(buf, OTX2_ALIGN);
    iova = dma_map_single_attrs(pfvf->dev, buf, pool->rbsize,
                                DMA_FROM_DEVICE, DMA_ATTR_SKIP_CPU_SYNC);
    if (unlikely(dma_mapping_error(pfvf->dev, iova))) {
--

2.29.2

Doesn't that break the 'free' code ?
Surely it needs the original pointer.

Why do we care about the original pointer? The free code should work with
the mangling poiner. Did I miss something?

quoted

I too agree, put_page(buf) or put_page(buf + OTX2_ALIGN) is same.