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

[Sunil Kovvuri <sunil.kovvuri@gmail.com>]

On Thu, Jan 21, 2021 at 5:26 PM Kevin Hao <haokexin@gmail.com> wrote:
>
> On Thu, Jan 21, 2021 at 09:53:08AM +0000, David Laight wrote:
> > From: Kevin Hao
> > > 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 <haokexin@gmail.com>
> > > ---
> > >  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?
>
> >

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