From: "Måns Rullgård" <mans@mansr•com>
To: Christophe Leroy <christophe.leroy@csgroup•eu>
Cc: Pantelis Antoniou <pantelis.antoniou@gmail•com>,
"David S. Miller" <davem@davemloft•net>,
Eric Dumazet <edumazet@google•com>,
Jakub Kicinski <kuba@kernel•org>, Paolo Abeni <pabeni@redhat•com>,
Vitaly Bordug <vbordug@ru•mvista.com>,
Dan Malek <dan@embeddededge•com>,
Joakim Tjernlund <joakim.tjernlund@lumentis•se>,
"linuxppc-dev@lists•ozlabs.org" <linuxppc-dev@lists•ozlabs.org>,
"netdev@vger•kernel.org" <netdev@vger•kernel.org>,
"linux-kernel@vger•kernel.org" <linux-kernel@vger•kernel.org>
Subject: Re: [PATCH] net: fs_enet: sync rx dma buffer before reading
Date: Fri, 20 May 2022 13:35:48 +0100 [thread overview]
Message-ID: <yw1xmtfc9yaj.fsf@mansr.com> (raw)
In-Reply-To: <03f24864-9d4d-b4f9-354a-f3b271c0ae66@csgroup.eu> (Christophe Leroy's message of "Fri, 20 May 2022 05:39:38 +0000")
Christophe Leroy <christophe.leroy@csgroup•eu> writes:
> Le 19/05/2022 à 21:24, Mans Rullgard a écrit :
>> The dma_sync_single_for_cpu() call must precede reading the received
>> data. Fix this.
>
> See original commit 070e1f01827c. It explicitely says that the cache
> must be invalidate _AFTER_ the copy.
>
> The cache is initialy invalidated by dma_map_single(), so before the
> copy the cache is already clean.
>
> After the copy, data is in the cache. In order to allow re-use of the
> skb, it must be put back in the same condition as before, in extenso the
> cache must be invalidated in order to be in the same situation as after
> dma_map_single().
>
> So I think your change is wrong.
OK, looking at it more closely, the change is at least unnecessary since
there will be a cache invalidation between each use of the buffer either
way. Please disregard the patch. Sorry for the noise.
>>
>> Fixes: 070e1f01827c ("net: fs_enet: don't unmap DMA when packet len is below copybreak")
>> Signed-off-by: Mans Rullgard <mans@mansr•com>
>> ---
>> drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c | 8 ++++----
>> 1 file changed, 4 insertions(+), 4 deletions(-)
>>
>> diff --git a/drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c b/drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c
>> index b3dae17e067e..432ce10cbfd0 100644
>> --- a/drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c
>> +++ b/drivers/net/ethernet/freescale/fs_enet/fs_enet-main.c
>> @@ -240,14 +240,14 @@ static int fs_enet_napi(struct napi_struct *napi, int budget)
>> /* +2 to make IP header L1 cache aligned */
>> skbn = netdev_alloc_skb(dev, pkt_len + 2);
>> if (skbn != NULL) {
>> + dma_sync_single_for_cpu(fep->dev,
>> + CBDR_BUFADDR(bdp),
>> + L1_CACHE_ALIGN(pkt_len),
>> + DMA_FROM_DEVICE);
>> skb_reserve(skbn, 2); /* align IP header */
>> skb_copy_from_linear_data(skb,
>> skbn->data, pkt_len);
>> swap(skb, skbn);
>> - dma_sync_single_for_cpu(fep->dev,
>> - CBDR_BUFADDR(bdp),
>> - L1_CACHE_ALIGN(pkt_len),
>> - DMA_FROM_DEVICE);
>> }
>> } else {
>> skbn = netdev_alloc_skb(dev, ENET_RX_FRSIZE);
>> --
>> 2.35.1
>>
--
Måns Rullgård
next prev parent reply other threads:[~2022-05-20 12:42 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-05-19 19:24 [PATCH] net: fs_enet: sync rx dma buffer before reading Mans Rullgard
2022-05-20 5:39 ` Christophe Leroy
2022-05-20 12:35 ` Måns Rullgård [this message]
2022-05-20 12:54 ` Christophe Leroy
2022-05-20 17:43 ` Jakub Kicinski
2022-05-21 6:44 ` Christophe Leroy
2022-05-21 17:44 ` Jakub Kicinski
2022-05-23 20:23 ` Jakub Kicinski
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