netdev - Re: [PATCH v3 net-next 2/6] net: mvneta: Use cacheable memory to store the rx buffer virtual address

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Message-ID: <87oa0yfu48.fsf@free-electrons.com>
Date:   Tue, 29 Nov 2016 11:39:03 +0100
From:   Gregory CLEMENT <gregory.clement@...e-electrons.com>
To:     Marcin Wojtas <mw@...ihalf.com>
Cc:     "David S. Miller" <davem@...emloft.net>,
        linux-kernel@...r.kernel.org, netdev@...r.kernel.org,
        Jisheng Zhang <jszhang@...vell.com>,
        Arnd Bergmann <arnd@...db.de>,
        Jason Cooper <jason@...edaemon.net>,
        Andrew Lunn <andrew@...n.ch>,
        Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>,
        Thomas Petazzoni <thomas.petazzoni@...e-electrons.com>,
        "linux-arm-kernel\@lists.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        Nadav Haklai <nadavh@...vell.com>,
        Dmitri Epshtein <dima@...vell.com>,
        Yelena Krivosheev <yelena@...vell.com>
Subject: Re: [PATCH v3 net-next 2/6] net: mvneta: Use cacheable memory to store the rx buffer virtual address

Hi Marcin,
 
 On mar., nov. 29 2016, Marcin Wojtas <mw@...ihalf.com> wrote:

> Gregory,
>
> 2016-11-29 11:19 GMT+01:00 Gregory CLEMENT <gregory.clement@...e-electrons.com>:
>> Hi Marcin,
>>
>>  On mar., nov. 29 2016, Marcin Wojtas <mw@...ihalf.com> wrote:
>>
>>> Hi Gregory,
>>>
>>> Another remark below, sorry for noise.
>>>
>>> 2016-11-29 10:37 GMT+01:00 Gregory CLEMENT <gregory.clement@...e-electrons.com>:
>>>> Until now the virtual address of the received buffer were stored in the
>>>> cookie field of the rx descriptor. However, this field is 32-bits only
>>>> which prevents to use the driver on a 64-bits architecture.
>>>>
>>>> With this patch the virtual address is stored in an array not shared with
>>>> the hardware (no more need to use the DMA API). Thanks to this, it is
>>>> possible to use cache contrary to the access of the rx descriptor member.
>>>>
>>>> The change is done in the swbm path only because the hwbm uses the cookie
>>>> field, this also means that currently the hwbm is not usable in 64-bits.
>>>>
>>>> Signed-off-by: Gregory CLEMENT <gregory.clement@...e-electrons.com>
>>>> ---
>>>>  drivers/net/ethernet/marvell/mvneta.c | 93 ++++++++++++++++++++++++----
>>>>  1 file changed, 81 insertions(+), 12 deletions(-)
>>>>
>>>> diff --git a/drivers/net/ethernet/marvell/mvneta.c b/drivers/net/ethernet/marvell/mvneta.c
>>>> index 1b84f746d748..32b142d0e44e 100644
>>>> --- a/drivers/net/ethernet/marvell/mvneta.c
>>>> +++ b/drivers/net/ethernet/marvell/mvneta.c
>>>> @@ -561,6 +561,9 @@ struct mvneta_rx_queue {
>>>>         u32 pkts_coal;
>>>>         u32 time_coal;
>>>>
>>>> +       /* Virtual address of the RX buffer */
>>>> +       void  **buf_virt_addr;
>>>> +
>>>>         /* Virtual address of the RX DMA descriptors array */
>>>>         struct mvneta_rx_desc *descs;
>>>>
>>>> @@ -1573,10 +1576,14 @@ static void mvneta_tx_done_pkts_coal_set(struct mvneta_port *pp,
>>>>
>>>>  /* Handle rx descriptor fill by setting buf_cookie and buf_phys_addr */
>>>>  static void mvneta_rx_desc_fill(struct mvneta_rx_desc *rx_desc,
>>>> -                               u32 phys_addr, u32 cookie)
>>>> +                               u32 phys_addr, void *virt_addr,
>>>> +                               struct mvneta_rx_queue *rxq)
>>>>  {
>>>> -       rx_desc->buf_cookie = cookie;
>>>> +       int i;
>>>> +
>>>>         rx_desc->buf_phys_addr = phys_addr;
>>>> +       i = rx_desc - rxq->descs;
>>>> +       rxq->buf_virt_addr[i] = virt_addr;
>>>>  }
>>>>
>>>>  /* Decrement sent descriptors counter */
>>>> @@ -1781,7 +1788,8 @@ EXPORT_SYMBOL_GPL(mvneta_frag_free);
>>>>
>>>>  /* Refill processing for SW buffer management */
>>>>  static int mvneta_rx_refill(struct mvneta_port *pp,
>>>> -                           struct mvneta_rx_desc *rx_desc)
>>>> +                           struct mvneta_rx_desc *rx_desc,
>>>> +                           struct mvneta_rx_queue *rxq)
>>>>
>>>>  {
>>>>         dma_addr_t phys_addr;
>>>> @@ -1799,7 +1807,7 @@ static int mvneta_rx_refill(struct mvneta_port *pp,
>>>>                 return -ENOMEM;
>>>>         }
>>>>
>>>> -       mvneta_rx_desc_fill(rx_desc, phys_addr, (u32)data);
>>>> +       mvneta_rx_desc_fill(rx_desc, phys_addr, data, rxq);
>>>>         return 0;
>>>>  }
>>>>
>>>> @@ -1861,7 +1869,12 @@ static void mvneta_rxq_drop_pkts(struct mvneta_port *pp,
>>>>
>>>>         for (i = 0; i < rxq->size; i++) {
>>>>                 struct mvneta_rx_desc *rx_desc = rxq->descs + i;
>>>> -               void *data = (void *)rx_desc->buf_cookie;
>>>> +               void *data;
>>>> +
>>>> +               if (!pp->bm_priv)
>>>> +                       data = rxq->buf_virt_addr[i];
>>>> +               else
>>>> +                       data = (void *)(uintptr_t)rx_desc->buf_cookie;
>>>
>>> Dropping packets for HWBM (in fact returning dropped buffers to the
>>> pool) is done a couple of lines above. This point will never be
>>
>> indeed I changed the code at every place the buf_cookie was used and
>> missed the fact that for HWBM this code was never reached.
>>
>>> reached with HWBM enabled (and it's also incorrect).
>>
>> What is incorrect?
>>
>
> Possible dma_unmapping + mvneta_frag_free for buffers in HWBM, when
> dropping packets.

Yes sure, but as you mentioned this code is never reached when HWBM is
enabled. I thought there was other part of the code to fix.

Thanks,

Gregory

>
> Thanks,
> Marcin

-- 
Gregory Clement, Free Electrons
Kernel, drivers, real-time and embedded Linux
development, consulting, training and support.
http://free-electrons.com