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linux/drivers/net/ethernet/stmicro/stmmac/dwmac1000_dma.c
Rohan G Thomas 45d100ee0d net: stmmac: dwmac: Disable flushing frames on Rx Buffer Unavailable 
In Store and Forward mode, flushing frames when the receive buffer is
unavailable, can cause the MTL Rx FIFO to go out of sync. This results
in buffering of a few frames in the FIFO without triggering Rx DMA
from transferring the data to the system memory until another packet
is received. Once the issue happens, for a ping request, the packet is
forwarded to the system memory only after we receive another packet
and hece we observe a latency equivalent to the ping interval.

64 bytes from 192.168.2.100: seq=1 ttl=64 time=1000.344 ms

Also, we can observe constant gmacgrp_debug register value of
0x00000120, which indicates "Reading frame data".

The issue is not reproducible after disabling frame flushing when Rx
buffer is unavailable. But in that case, the Rx DMA enters a suspend
state due to buffer unavailability. To resume operation, software
must write to the receive_poll_demand register after adding new
descriptors, which reactivates the Rx DMA.

This issue is observed in the socfpga platforms which has dwmac1000 IP
like Arria 10, Cyclone V and Agilex 7. Issue is reproducible after
running iperf3 server at the DUT for UDP lower packet sizes.

Signed-off-by: Rohan G Thomas <rohan.g.thomas@altera.com>
Reviewed-by: Matthew Gerlach <matthew.gerlach@altera.com>
Tested-by: Maxime Chevallier <maxime.chevallier@bootlin.com>
Reviewed-by: Russell King (Oracle) <rmk+kernel@armlinux.org.uk>
Link: https://patch.msgid.link/20251126-a10_ext_fix-v1-1-d163507f646f@altera.com
Signed-off-by: Paolo Abeni <pabeni@redhat.com>
2025-11-27 13:05:24 +01:00

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// SPDX-License-Identifier: GPL-2.0-only
/*******************************************************************************
This is the driver for the GMAC on-chip Ethernet controller for ST SoCs.
DWC Ether MAC 10/100/1000 Universal version 3.41a has been used for
developing this code.
This contains the functions to handle the dma.
Copyright (C) 2007-2009 STMicroelectronics Ltd
Author: Giuseppe Cavallaro <peppe.cavallaro@st.com>
*******************************************************************************/
#include <linux/io.h>
#include "dwmac1000.h"
#include "dwmac_dma.h"
static void dwmac1000_dma_axi(void __iomem *ioaddr, struct stmmac_axi *axi)
{
u32 value = readl(ioaddr + DMA_AXI_BUS_MODE);
pr_info("dwmac1000: Master AXI performs %s burst length\n",
!(value & DMA_AXI_UNDEF) ? "fixed" : "any");
if (axi->axi_lpi_en)
value |= DMA_AXI_EN_LPI;
if (axi->axi_xit_frm)
value |= DMA_AXI_LPI_XIT_FRM;
value &= ~DMA_AXI_WR_OSR_LMT;
value |= (axi->axi_wr_osr_lmt & DMA_AXI_WR_OSR_LMT_MASK) <<
DMA_AXI_WR_OSR_LMT_SHIFT;
value &= ~DMA_AXI_RD_OSR_LMT;
value |= (axi->axi_rd_osr_lmt & DMA_AXI_RD_OSR_LMT_MASK) <<
DMA_AXI_RD_OSR_LMT_SHIFT;
/* Depending on the UNDEF bit the Master AXI will perform any burst
* length according to the BLEN programmed (by default all BLEN are
* set). Note that the UNDEF bit is readonly, and is the inverse of
* Bus Mode bit 16.
*/
value = (value & ~DMA_AXI_BLEN_MASK) | axi->axi_blen_regval;
writel(value, ioaddr + DMA_AXI_BUS_MODE);
}
static void dwmac1000_dma_init_channel(struct stmmac_priv *priv,
void __iomem *ioaddr,
struct stmmac_dma_cfg *dma_cfg, u32 chan)
{
int txpbl = dma_cfg->txpbl ?: dma_cfg->pbl;
int rxpbl = dma_cfg->rxpbl ?: dma_cfg->pbl;
u32 value;
value = readl(ioaddr + DMA_CHAN_BUS_MODE(chan));
/* Set the DMA PBL (Programmable Burst Length) mode.
*
* Note: before stmmac core 3.50 this mode bit was 4xPBL, and
* post 3.5 mode bit acts as 8*PBL.
*/
if (dma_cfg->pblx8)
value |= DMA_BUS_MODE_MAXPBL;
value |= DMA_BUS_MODE_USP;
value &= ~(DMA_BUS_MODE_PBL_MASK | DMA_BUS_MODE_RPBL_MASK);
value |= (txpbl << DMA_BUS_MODE_PBL_SHIFT);
value |= (rxpbl << DMA_BUS_MODE_RPBL_SHIFT);
/* Set the Fixed burst mode */
if (dma_cfg->fixed_burst)
value |= DMA_BUS_MODE_FB;
/* Mixed Burst has no effect when fb is set */
if (dma_cfg->mixed_burst)
value |= DMA_BUS_MODE_MB;
if (dma_cfg->atds)
value |= DMA_BUS_MODE_ATDS;
if (dma_cfg->aal)
value |= DMA_BUS_MODE_AAL;
writel(value, ioaddr + DMA_CHAN_BUS_MODE(chan));
/* Mask interrupts by writing to CSR7 */
writel(DMA_INTR_DEFAULT_MASK, ioaddr + DMA_CHAN_INTR_ENA(chan));
}
static void dwmac1000_dma_init_rx(struct stmmac_priv *priv,
void __iomem *ioaddr,
struct stmmac_dma_cfg *dma_cfg,
dma_addr_t dma_rx_phy, u32 chan)
{
/* RX descriptor base address list must be written into DMA CSR3 */
writel(lower_32_bits(dma_rx_phy), ioaddr + DMA_CHAN_RCV_BASE_ADDR(chan));
}
static void dwmac1000_dma_init_tx(struct stmmac_priv *priv,
void __iomem *ioaddr,
struct stmmac_dma_cfg *dma_cfg,
dma_addr_t dma_tx_phy, u32 chan)
{
/* TX descriptor base address list must be written into DMA CSR4 */
writel(lower_32_bits(dma_tx_phy), ioaddr + DMA_CHAN_TX_BASE_ADDR(chan));
}
static u32 dwmac1000_configure_fc(u32 csr6, int rxfifosz)
{
csr6 &= ~DMA_CONTROL_RFA_MASK;
csr6 &= ~DMA_CONTROL_RFD_MASK;
/* Leave flow control disabled if receive fifo size is less than
* 4K or 0. Otherwise, send XOFF when fifo is 1K less than full,
* and send XON when 2K less than full.
*/
if (rxfifosz < 4096) {
csr6 &= ~DMA_CONTROL_EFC;
pr_debug("GMAC: disabling flow control, rxfifo too small(%d)\n",
rxfifosz);
} else {
csr6 |= DMA_CONTROL_EFC;
csr6 |= RFA_FULL_MINUS_1K;
csr6 |= RFD_FULL_MINUS_2K;
}
return csr6;
}
static void dwmac1000_dma_operation_mode_rx(struct stmmac_priv *priv,
void __iomem *ioaddr, int mode,
u32 channel, int fifosz, u8 qmode)
{
u32 csr6 = readl(ioaddr + DMA_CHAN_CONTROL(channel));
if (mode == SF_DMA_MODE) {
pr_debug("GMAC: enable RX store and forward mode\n");
csr6 |= DMA_CONTROL_RSF | DMA_CONTROL_DFF;
} else {
pr_debug("GMAC: disable RX SF mode (threshold %d)\n", mode);
csr6 &= ~(DMA_CONTROL_RSF | DMA_CONTROL_DFF);
csr6 &= DMA_CONTROL_TC_RX_MASK;
if (mode <= 32)
csr6 |= DMA_CONTROL_RTC_32;
else if (mode <= 64)
csr6 |= DMA_CONTROL_RTC_64;
else if (mode <= 96)
csr6 |= DMA_CONTROL_RTC_96;
else
csr6 |= DMA_CONTROL_RTC_128;
}
/* Configure flow control based on rx fifo size */
csr6 = dwmac1000_configure_fc(csr6, fifosz);
writel(csr6, ioaddr + DMA_CHAN_CONTROL(channel));
}
static void dwmac1000_dma_operation_mode_tx(struct stmmac_priv *priv,
void __iomem *ioaddr, int mode,
u32 channel, int fifosz, u8 qmode)
{
u32 csr6 = readl(ioaddr + DMA_CHAN_CONTROL(channel));
if (mode == SF_DMA_MODE) {
pr_debug("GMAC: enable TX store and forward mode\n");
/* Transmit COE type 2 cannot be done in cut-through mode. */
csr6 |= DMA_CONTROL_TSF;
/* Operating on second frame increase the performance
* especially when transmit store-and-forward is used.
*/
csr6 |= DMA_CONTROL_OSF;
} else {
pr_debug("GMAC: disabling TX SF (threshold %d)\n", mode);
csr6 &= ~DMA_CONTROL_TSF;
csr6 &= DMA_CONTROL_TC_TX_MASK;
/* Set the transmit threshold */
if (mode <= 32)
csr6 |= DMA_CONTROL_TTC_32;
else if (mode <= 64)
csr6 |= DMA_CONTROL_TTC_64;
else if (mode <= 128)
csr6 |= DMA_CONTROL_TTC_128;
else if (mode <= 192)
csr6 |= DMA_CONTROL_TTC_192;
else
csr6 |= DMA_CONTROL_TTC_256;
}
writel(csr6, ioaddr + DMA_CHAN_CONTROL(channel));
}
static void dwmac1000_dump_dma_regs(struct stmmac_priv *priv,
void __iomem *ioaddr, u32 *reg_space)
{
int i;
for (i = 0; i < NUM_DWMAC1000_DMA_REGS; i++)
if ((i < 12) || (i > 17))
reg_space[DMA_BUS_MODE / 4 + i] =
readl(ioaddr + DMA_BUS_MODE + i * 4);
}
static int dwmac1000_get_hw_feature(void __iomem *ioaddr,
struct dma_features *dma_cap)
{
u32 hw_cap = readl(ioaddr + DMA_HW_FEATURE);
if (!hw_cap) {
/* 0x00000000 is the value read on old hardware that does not
* implement this register
*/
return -EOPNOTSUPP;
}
dma_cap->mbps_10_100 = (hw_cap & DMA_HW_FEAT_MIISEL);
dma_cap->mbps_1000 = (hw_cap & DMA_HW_FEAT_GMIISEL) >> 1;
dma_cap->half_duplex = (hw_cap & DMA_HW_FEAT_HDSEL) >> 2;
dma_cap->hash_filter = (hw_cap & DMA_HW_FEAT_HASHSEL) >> 4;
dma_cap->multi_addr = (hw_cap & DMA_HW_FEAT_ADDMAC) >> 5;
dma_cap->pcs = (hw_cap & DMA_HW_FEAT_PCSSEL) >> 6;
dma_cap->sma_mdio = (hw_cap & DMA_HW_FEAT_SMASEL) >> 8;
dma_cap->pmt_remote_wake_up = (hw_cap & DMA_HW_FEAT_RWKSEL) >> 9;
dma_cap->pmt_magic_frame = (hw_cap & DMA_HW_FEAT_MGKSEL) >> 10;
/* MMC */
dma_cap->rmon = (hw_cap & DMA_HW_FEAT_MMCSEL) >> 11;
/* IEEE 1588-2002 */
dma_cap->time_stamp =
(hw_cap & DMA_HW_FEAT_TSVER1SEL) >> 12;
/* IEEE 1588-2008 */
dma_cap->atime_stamp = (hw_cap & DMA_HW_FEAT_TSVER2SEL) >> 13;
/* 802.3az - Energy-Efficient Ethernet (EEE) */
dma_cap->eee = (hw_cap & DMA_HW_FEAT_EEESEL) >> 14;
dma_cap->av = (hw_cap & DMA_HW_FEAT_AVSEL) >> 15;
/* TX and RX csum */
dma_cap->tx_coe = (hw_cap & DMA_HW_FEAT_TXCOESEL) >> 16;
dma_cap->rx_coe_type1 = (hw_cap & DMA_HW_FEAT_RXTYP1COE) >> 17;
dma_cap->rx_coe_type2 = (hw_cap & DMA_HW_FEAT_RXTYP2COE) >> 18;
dma_cap->rxfifo_over_2048 = (hw_cap & DMA_HW_FEAT_RXFIFOSIZE) >> 19;
/* TX and RX number of channels */
dma_cap->number_rx_channel = (hw_cap & DMA_HW_FEAT_RXCHCNT) >> 20;
dma_cap->number_tx_channel = (hw_cap & DMA_HW_FEAT_TXCHCNT) >> 22;
/* Alternate (enhanced) DESC mode */
dma_cap->enh_desc = (hw_cap & DMA_HW_FEAT_ENHDESSEL) >> 24;
return 0;
}
static void dwmac1000_rx_watchdog(struct stmmac_priv *priv,
void __iomem *ioaddr, u32 riwt, u32 queue)
{
writel(riwt, ioaddr + DMA_CHAN_RX_WATCHDOG(queue));
}
const struct stmmac_dma_ops dwmac1000_dma_ops = {
.reset = dwmac_dma_reset,
.init_chan = dwmac1000_dma_init_channel,
.init_rx_chan = dwmac1000_dma_init_rx,
.init_tx_chan = dwmac1000_dma_init_tx,
.axi = dwmac1000_dma_axi,
.dump_regs = dwmac1000_dump_dma_regs,
.dma_rx_mode = dwmac1000_dma_operation_mode_rx,
.dma_tx_mode = dwmac1000_dma_operation_mode_tx,
.enable_dma_transmission = dwmac_enable_dma_transmission,
.enable_dma_reception = dwmac_enable_dma_reception,
.enable_dma_irq = dwmac_enable_dma_irq,
.disable_dma_irq = dwmac_disable_dma_irq,
.start_tx = dwmac_dma_start_tx,
.stop_tx = dwmac_dma_stop_tx,
.start_rx = dwmac_dma_start_rx,
.stop_rx = dwmac_dma_stop_rx,
.dma_interrupt = dwmac_dma_interrupt,
.get_hw_feature = dwmac1000_get_hw_feature,
.rx_watchdog = dwmac1000_rx_watchdog,
};
EXPORT_SYMBOL_GPL(dwmac1000_dma_ops);
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