Message ID | 25eeec13-8aed-b715-2f06-54dbf04825d4@linux.intel.com |
---|---|
State | RFC, archived |
Delegated to: | David Miller |
Headers | show |
Series | [RFC] net: stmmac: RX Jumbo packet size > 8191 problem | expand |
On 25-10-2018 21:41, Thor Thayer wrote: > Hi, > > I'm running into a weird issue at the DMA boundary for large > packets (>8192) that I can't explain. I'm hoping someone here > has an idea on why I'm seeing this issue. > > This is the Synopsys DesignWare Ethernet GMAC core (3.74) using > the stmmac driver found at drivers/net/ethernet/stmicro/stmmac. > > If I ping with data sizes that exceed the first DMA buffer size > (size set to 8191), ping reports a data mismatch as follows at > byte #8144: > > $ ping -c 1 -M do -s 8150 192.168.1.99 > PING 192.168.1.99 (192.168.1.99) 8150(8178) bytes of data. > 8158 bytes from 192.168.1.99: icmp_seq=1 ttl=64 time=0.669 ms > wrong data byte #8144 should be 0xd0 but was 0x0 > #16 10 11 12 13 14 15 16 17 18 19 1a 1b 1c 1d 1e 1f 20 21 22 > 23 24 25 26 27 28 29 2a 2b 2c 2d 2e 2f > %< ---------------snip-------------------------------------- > #8112 b0 b1 b2 b3 b4 b5 b6 b7 b8 b9 ba bb bc bd be bf c0 c1 > c2 c3 c4 c5 c6 c7 c8 c9 ca cb cc cd ce cf > #8144 0 0 0 0 d0 d1 > ^^^^^^^ > Notice the 4 bytes of 0 there before the expected byte of d0. I > confirmed the on-wire result with wireshark - same data packet > as shown above. > > Looking at the queue, I'm seeing these values in the RX > descriptors (I'm using ring mode, enhanced descriptors). > 0xa0040320 0x9fff1fff 0x7a358042 0x7a35a042 > ^des0 ^des1 ^des2 ^desc3 > > desc0 => 8196 bytes, OWN, First & Last Descriptor, Frame type = > Eth > desc1 => Disable IRQ on done, Rx Buffer2 sz = 8191, Rx Buffer1 > sz = 8191 > desc2 => Buffer 1 Addr Pointer > desc3 => Buffer 2 Addr Pointer > > If I adjust init_desc3() and refill_desc3() to initialize desc3 > to desc2+BUF_SIZE_8KiB-4, I get a descriptor as show below and > ping completes successfully. > 0xa0040320 0x9fff1fff 0x77df8042 0x77dfa03e > ^ this is now different > > But I'm not sure why the -4 works because desc3 overlaps into > the end of the first DMA buffer area (des2) which is > counterintuitive. By databook you have to set buffer size as multiple of bus width but you are setting 8191 so this is not correct. Can you try changing ehn_desc_rx_set_on_ring() and remove the subtraction, as well as in enh_desc_init_rx_desc() ? Thanks and Best Regards, Jose Miguel Abreu
diff --git a/drivers/net/ethernet/stmicro/stmmac/ring_mode.c b/drivers/net/ethernet/stmicro/stmmac/ring_mode.c index abc3f85270cd..b52be0235d8f 100644 --- a/drivers/net/ethernet/stmicro/stmmac/ring_mode.c +++ b/drivers/net/ethernet/stmicro/stmmac/ring_mode.c @@ -115,13 +115,13 @@ static void refill_desc3(void *priv_ptr, struct dma_desc *p) /* Fill DES3 in case of RING mode */ if (priv->dma_buf_sz >= BUF_SIZE_8KiB) - p->des3 = cpu_to_le32(le32_to_cpu(p->des2) + BUF_SIZE_8KiB); + p->des3 = cpu_to_le32(le32_to_cpu(p->des2) + + BUF_SIZE_8KiB - 4); } /* In ring mode we need to fill the desc3 because it is used as buffer */ static void init_desc3(struct dma_desc *p) { - p->des3 = cpu_to_le32(le32_to_cpu(p->des2) + BUF_SIZE_8KiB); + p->des3 = cpu_to_le32(le32_to_cpu(p->des2) + BUF_SIZE_8KiB - 4); }