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Diffstat (limited to 'Documentation')
| -rw-r--r-- | Documentation/networking/stmmac.txt | 143 |
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diff --git a/Documentation/networking/stmmac.txt b/Documentation/networking/stmmac.txt new file mode 100644 index 000000000000..7ee770b5ef5f --- /dev/null +++ b/Documentation/networking/stmmac.txt @@ -0,0 +1,143 @@ + STMicroelectronics 10/100/1000 Synopsys Ethernet driver + +Copyright (C) 2007-2010 STMicroelectronics Ltd +Author: Giuseppe Cavallaro <peppe.cavallaro@st.com> + +This is the driver for the MAC 10/100/1000 on-chip Ethernet controllers +(Synopsys IP blocks); it has been fully tested on STLinux platforms. + +Currently this network device driver is for all STM embedded MAC/GMAC +(7xxx SoCs). + +DWC Ether MAC 10/100/1000 Universal version 3.41a and DWC Ether MAC 10/100 +Universal version 4.0 have been used for developing the first code +implementation. + +Please, for more information also visit: www.stlinux.com + +1) Kernel Configuration +The kernel configuration option is STMMAC_ETH: + Device Drivers ---> Network device support ---> Ethernet (1000 Mbit) ---> + STMicroelectronics 10/100/1000 Ethernet driver (STMMAC_ETH) + +2) Driver parameters list: + debug: message level (0: no output, 16: all); + phyaddr: to manually provide the physical address to the PHY device; + dma_rxsize: DMA rx ring size; + 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: + stmmaceth=dma_rxsize:128,dma_txsize:512 + +4) Driver information and notes + +4.1) Transmit process +The xmit method is invoked when the kernel needs to transmit a packet; it sets +the descriptors in the ring and informs the DMA engine that there is a packet +ready to be transmitted. +Once the controller has finished transmitting the packet, an interrupt is +triggered; So the driver will be able to release the socket buffers. +By default, the driver sets the NETIF_F_SG bit in the features field of the +net_device structure enabling the scatter/gather feature. + +4.2) Receive process +When one or more packets are received, an interrupt happens. The interrupts +are not queued so the driver has to scan all the descriptors in the ring during +the receive process. +This is based on NAPI so the interrupt handler signals only if there is work to be +done, and it exits. +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. + +4.4) WOL +Wake up on Lan feature through Magic Frame is only supported for the GMAC +core. + +4.5) DMA descriptors +Driver handles both normal and enhanced descriptors. The latter has been only +tested on DWC Ether MAC 10/100/1000 Universal version 3.41a. + +4.6) Ethtool support +Ethtool is supported. Driver statistics and internal errors can be taken using: +ethtool -S ethX command. It is possible to dump registers etc. + +4.7) Jumbo and Segmentation Offloading +Jumbo frames are supported and tested for the GMAC. +The GSO has been also added but it's performed in software. +LRO is not supported. + +4.8) Physical +The driver is compatible with PAL to work with PHY and GPHY devices. + +4.9) Platform information +Several information came from the platform; please refer to the +driver's Header file in include/linux directory. + +struct plat_stmmacenet_data { + int bus_id; + int pbl; + int has_gmac; + void (*fix_mac_speed)(void *priv, unsigned int speed); + void (*bus_setup)(unsigned long ioaddr); +#ifdef CONFIG_STM_DRIVERS + struct stm_pad_config *pad_config; +#endif + void *bsp_priv; +}; + +Where: +- pbl (Programmable Burst Length) is maximum number of + beats to be transferred in one DMA transaction. + GMAC also enables the 4xPBL by default. +- fix_mac_speed and bus_setup are used to configure internal target + registers (on STM platforms); +- has_gmac: GMAC core is on board (get it at run-time in the next step); +- bus_id: bus identifier. + +struct plat_stmmacphy_data { + int bus_id; + int phy_addr; + unsigned int phy_mask; + int interface; + int (*phy_reset)(void *priv); + void *priv; +}; + +Where: +- bus_id: bus identifier; +- phy_addr: physical address used for the attached phy device; + set it to -1 to get it at run-time; +- interface: physical MII interface mode; +- phy_reset: hook to reset HW function. + +TODO: +- Continue to make the driver more generic and suitable for other Synopsys + Ethernet controllers used on other architectures (i.e. ARM). +- 10G controllers are not supported. +- MAC uses Normal descriptors and GMAC uses enhanced ones. + This is a limit that should be reviewed. MAC could want to + use the enhanced structure. +- Checksumming: Rx/Tx csum is done in HW in case of GMAC only. +- Review the timer optimisation code to use an embedded device that seems to be + available in new chip generations. |