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

From: Gregory CLEMENT
Date: Tue Nov 29 2016 - 05:39:21 EST


Hi Marcin,

On mar., nov. 29 2016, Marcin Wojtas <mw@xxxxxxxxxxxx> wrote:

> Gregory,
>
> 2016-11-29 11:19 GMT+01:00 Gregory CLEMENT <gregory.clement@xxxxxxxxxxxxxxxxxx>:
>> Hi Marcin,
>>
>> On mar., nov. 29 2016, Marcin Wojtas <mw@xxxxxxxxxxxx> wrote:
>>
>>> Hi Gregory,
>>>
>>> Another remark below, sorry for noise.
>>>
>>> 2016-11-29 10:37 GMT+01:00 Gregory CLEMENT <gregory.clement@xxxxxxxxxxxxxxxxxx>:
>>>> 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@xxxxxxxxxxxxxxxxxx>
>>>> ---
>>>> 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