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 [off-list ref] wrote:

Gregory,

2016-11-29 11:19 GMT+01:00 Gregory CLEMENT [off-list ref]:

quoted

Hi Marcin,

 On mar., nov. 29 2016, Marcin Wojtas [off-list ref] wrote:

quoted

Hi Gregory,

Another remark below, sorry for noise.

2016-11-29 10:37 GMT+01:00 Gregory CLEMENT [off-list ref]:

quoted

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 <redacted>
---
 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.

quoted

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