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stmmac: update the doc with new IRQ mitigation

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This patch updates the stmmac.txt adding some information
about the new rx/tx mitigation schema adopted in the driver.

Signed-off-by: Giuseppe Cavallaro <peppe.cavallaro@st.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Giuseppe CAVALLARO 2012-11-25 23:10:45 +00:00 committed by David S. Miller
parent 48f44da454
commit f9e01b5565
1 changed files with 15 additions and 13 deletions
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28
Documentation/networking/stmmac.txt
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@ -29,11 +29,9 @@ The kernel configuration option is STMMAC_ETH:
dma_txsize: DMA tx ring size;
buf_sz: DMA buffer size;
tc: control the HW FIFO threshold;
tx_coe: Enable/Disable Tx Checksum Offload engine;
watchdog: transmit timeout (in milliseconds);
flow_ctrl: Flow control ability [on/off];
pause: Flow Control Pause Time;
tmrate: timer period (only if timer optimisation is configured).
3) Command line options
Driver parameters can be also passed in command line by using:
@ -60,17 +58,19 @@ Then the poll method will be scheduled at some future point.
The incoming packets are stored, by the DMA, in a list of pre-allocated socket
buffers in order to avoid the memcpy (Zero-copy).
4.3) Timer-Driver Interrupt
Instead of having the device that asynchronously notifies the frame receptions,
the driver configures a timer to generate an interrupt at regular intervals.
Based on the granularity of the timer, the frames that are received by the
device will experience different levels of latency. Some NICs have dedicated
timer device to perform this task. STMMAC can use either the RTC device or the
TMU channel 2 on STLinux platforms.
The timers frequency can be passed to the driver as parameter; when change it,
take care of both hardware capability and network stability/performance impact.
Several performance tests on STM platforms showed this optimisation allows to
spare the CPU while having the maximum throughput.
4.3) Interrupt Mitigation
The driver is able to mitigate the number of its DMA interrupts
using NAPI for the reception on chips older than the 3.50.
New chips have an HW RX-Watchdog used for this mitigation.
On Tx-side, the mitigation schema is based on a SW timer that calls the
tx function (stmmac_tx) to reclaim the resource after transmitting the
frames.
Also there is another parameter (like a threshold) used to program
the descriptors avoiding to set the interrupt on completion bit in
when the frame is sent (xmit).
Mitigation parameters can be tuned by ethtool.
4.4) WOL
Wake up on Lan feature through Magic and Unicast frames are supported for the
@ -121,6 +121,7 @@ struct plat_stmmacenet_data {
int bugged_jumbo;
int pmt;
int force_sf_dma_mode;
int riwt_off;
void (*fix_mac_speed)(void *priv, unsigned int speed);
void (*bus_setup)(void __iomem *ioaddr);
int (*init)(struct platform_device *pdev);
@ -156,6 +157,7 @@ Where:
o pmt: core has the embedded power module (optional).
o force_sf_dma_mode: force DMA to use the Store and Forward mode
instead of the Threshold.
o riwt_off: force to disable the RX watchdog feature and switch to NAPI mode.
o fix_mac_speed: this callback is used for modifying some syscfg registers
(on ST SoCs) according to the link speed negotiated by the
physical layer .