About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Documentation / networking / stmmac.txt




Custom Search

Based on kernel version 4.13.3. Page generated on 2017-09-23 13:55 EST.

1	       STMicroelectronics 10/100/1000 Synopsys Ethernet driver
2	
3	Copyright (C) 2007-2015  STMicroelectronics Ltd
4	Author: Giuseppe Cavallaro <peppe.cavallaro@st.com>
5	
6	This is the driver for the MAC 10/100/1000 on-chip Ethernet controllers
7	(Synopsys IP blocks).
8	
9	Currently this network device driver is for all STi embedded MAC/GMAC
10	(i.e. 7xxx/5xxx SoCs), SPEAr (arm), Loongson1B (mips) and XLINX XC2V3000
11	FF1152AMT0221 D1215994A VIRTEX FPGA board.
12	
13	DWC Ether MAC 10/100/1000 Universal version 3.70a (and older) and DWC Ether
14	MAC 10/100 Universal version 4.0 have been used for developing this driver.
15	
16	This driver supports both the platform bus and PCI.
17	
18	Please, for more information also visit: www.stlinux.com
19	
20	1) Kernel Configuration
21	The kernel configuration option is STMMAC_ETH:
22	 Device Drivers ---> Network device support ---> Ethernet (1000 Mbit) --->
23	 STMicroelectronics 10/100/1000 Ethernet driver (STMMAC_ETH)
24	
25	CONFIG_STMMAC_PLATFORM: is to enable the platform driver.
26	CONFIG_STMMAC_PCI: is to enable the pci driver.
27	
28	2) Driver parameters list:
29		debug: message level (0: no output, 16: all);
30		phyaddr: to manually provide the physical address to the PHY device;
31		buf_sz: DMA buffer size;
32		tc: control the HW FIFO threshold;
33		watchdog: transmit timeout (in milliseconds);
34		flow_ctrl: Flow control ability [on/off];
35		pause: Flow Control Pause Time;
36		eee_timer: tx EEE timer;
37		chain_mode: select chain mode instead of ring.
38	
39	3) Command line options
40	Driver parameters can be also passed in command line by using:
41		stmmaceth=watchdog:100,chain_mode=1
42	
43	4) Driver information and notes
44	
45	4.1) Transmit process
46	The xmit method is invoked when the kernel needs to transmit a packet; it sets
47	the descriptors in the ring and informs the DMA engine, that there is a packet
48	ready to be transmitted.
49	By default, the driver sets the NETIF_F_SG bit in the features field of the
50	net_device structure, enabling the scatter-gather feature. This is true on
51	chips and configurations where the checksum can be done in hardware.
52	Once the controller has finished transmitting the packet, timer will be
53	scheduled to release the transmit resources.
54	
55	4.2) Receive process
56	When one or more packets are received, an interrupt happens. The interrupts
57	are not queued, so the driver has to scan all the descriptors in the ring during
58	the receive process.
59	This is based on NAPI, so the interrupt handler signals only if there is work
60	to be done, and it exits.
61	Then the poll method will be scheduled at some future point.
62	The incoming packets are stored, by the DMA, in a list of pre-allocated socket
63	buffers in order to avoid the memcpy (zero-copy).
64	
65	4.3) Interrupt mitigation
66	The driver is able to mitigate the number of its DMA interrupts
67	using NAPI for the reception on chips older than the 3.50.
68	New chips have an HW RX-Watchdog used for this mitigation.
69	Mitigation parameters can be tuned by ethtool.
70	
71	4.4) WOL
72	Wake up on Lan feature through Magic and Unicast frames are supported for the
73	GMAC core.
74	
75	4.5) DMA descriptors
76	Driver handles both normal and alternate descriptors. The latter has been only
77	tested on DWC Ether MAC 10/100/1000 Universal version 3.41a and later.
78	
79	STMMAC supports DMA descriptor to operate both in dual buffer (RING)
80	and linked-list(CHAINED) mode. In RING each descriptor points to two
81	data buffer pointers whereas in CHAINED mode they point to only one data
82	buffer pointer. RING mode is the default.
83	
84	In CHAINED mode each descriptor will have pointer to next descriptor in
85	the list, hence creating the explicit chaining in the descriptor itself,
86	whereas such explicit chaining is not possible in RING mode.
87	
88	4.5.1) Extended descriptors
89	The extended descriptors give us information about the Ethernet payload
90	when it is carrying PTP packets or TCP/UDP/ICMP over IP.
91	These are not available on GMAC Synopsys chips older than the 3.50.
92	At probe time the driver will decide if these can be actually used.
93	This support also is mandatory for PTPv2 because the extra descriptors
94	are used for saving the hardware timestamps and Extended Status.
95	
96	4.6) Ethtool support
97	Ethtool is supported.
98	
99	For example, driver statistics (including RMON), internal errors can be taken
100	using:
101	  # ethtool -S ethX
102	command
103	
104	4.7) Jumbo and Segmentation Offloading
105	Jumbo frames are supported and tested for the GMAC.
106	The GSO has been also added but it's performed in software.
107	LRO is not supported.
108	
109	4.8) Physical
110	The driver is compatible with Physical Abstraction Layer to be connected with
111	PHY and GPHY devices.
112	
113	4.9) Platform information
114	Several information can be passed through the platform and device-tree.
115	
116	struct plat_stmmacenet_data {
117		char *phy_bus_name;
118		int bus_id;
119		int phy_addr;
120		int interface;
121		struct stmmac_mdio_bus_data *mdio_bus_data;
122		struct stmmac_dma_cfg *dma_cfg;
123		int clk_csr;
124		int has_gmac;
125		int enh_desc;
126		int tx_coe;
127		int rx_coe;
128		int bugged_jumbo;
129		int pmt;
130		int force_sf_dma_mode;
131		int force_thresh_dma_mode;
132		int riwt_off;
133		int max_speed;
134		int maxmtu;
135		void (*fix_mac_speed)(void *priv, unsigned int speed);
136		void (*bus_setup)(void __iomem *ioaddr);
137		int (*init)(struct platform_device *pdev, void *priv);
138		void (*exit)(struct platform_device *pdev, void *priv);
139		void *bsp_priv;
140		int has_gmac4;
141		bool tso_en;
142	};
143	
144	Where:
145	 o phy_bus_name: phy bus name to attach to the stmmac.
146	 o bus_id: bus identifier.
147	 o phy_addr: the physical address can be passed from the platform.
148		    If it is set to -1 the driver will automatically
149		    detect it at run-time by probing all the 32 addresses.
150	 o interface: PHY device's interface.
151	 o mdio_bus_data: specific platform fields for the MDIO bus.
152	 o dma_cfg: internal DMA parameters
153	   o pbl: the Programmable Burst Length is maximum number of beats to
154	       be transferred in one DMA transaction.
155	       GMAC also enables the 4xPBL by default. (8xPBL for GMAC 3.50 and newer)
156	   o txpbl/rxpbl: GMAC and newer supports independent DMA pbl for tx/rx.
157	   o pblx8: Enable 8xPBL (4xPBL for core rev < 3.50). Enabled by default.
158	   o fixed_burst/mixed_burst/aal
159	 o clk_csr: fixed CSR Clock range selection.
160	 o has_gmac: uses the GMAC core.
161	 o enh_desc: if sets the MAC will use the enhanced descriptor structure.
162	 o tx_coe: core is able to perform the tx csum in HW.
163	 o rx_coe: the supports three check sum offloading engine types:
164		   type_1, type_2 (full csum) and no RX coe.
165	 o bugged_jumbo: some HWs are not able to perform the csum in HW for
166			over-sized frames due to limited buffer sizes.
167			Setting this flag the csum will be done in SW on
168			JUMBO frames.
169	 o pmt: core has the embedded power module (optional).
170	 o force_sf_dma_mode: force DMA to use the Store and Forward mode
171			     instead of the Threshold.
172	 o force_thresh_dma_mode: force DMA to use the Threshold mode other than
173			     the Store and Forward mode.
174	 o riwt_off: force to disable the RX watchdog feature and switch to NAPI mode.
175	 o fix_mac_speed: this callback is used for modifying some syscfg registers
176			 (on ST SoCs) according to the link speed negotiated by the
177			 physical layer .
178	 o bus_setup: perform HW setup of the bus. For example, on some ST platforms
179		     this field is used to configure the AMBA  bridge to generate more
180		     efficient STBus traffic.
181	 o init/exit: callbacks used for calling a custom initialization;
182		     this is sometime necessary on some platforms (e.g. ST boxes)
183		     where the HW needs to have set some PIO lines or system cfg
184		     registers.  init/exit callbacks should not use or modify
185		     platform data.
186	 o bsp_priv: another private pointer.
187	 o has_gmac4: uses GMAC4 core.
188	 o tso_en: Enables TSO (TCP Segmentation Offload) feature.
189	
190	For MDIO bus The we have:
191	
192	 struct stmmac_mdio_bus_data {
193		int (*phy_reset)(void *priv);
194		unsigned int phy_mask;
195		int *irqs;
196		int probed_phy_irq;
197	 };
198	
199	Where:
200	 o phy_reset: hook to reset the phy device attached to the bus.
201	 o phy_mask: phy mask passed when register the MDIO bus within the driver.
202	 o irqs: list of IRQs, one per PHY.
203	 o probed_phy_irq: if irqs is NULL, use this for probed PHY.
204	
205	For DMA engine we have the following internal fields that should be
206	tuned according to the HW capabilities.
207	
208	struct stmmac_dma_cfg {
209		int pbl;
210		int txpbl;
211		int rxpbl;
212		bool pblx8;
213		int fixed_burst;
214		int mixed_burst;
215		bool aal;
216	};
217	
218	Where:
219	 o pbl: Programmable Burst Length (tx and rx)
220	 o txpbl: Transmit Programmable Burst Length. Only for GMAC and newer.
221		 If set, DMA tx will use this value rather than pbl.
222	 o rxpbl: Receive Programmable Burst Length. Only for GMAC and newer.
223		 If set, DMA rx will use this value rather than pbl.
224	 o pblx8: Enable 8xPBL (4xPBL for core rev < 3.50). Enabled by default.
225	 o fixed_burst: program the DMA to use the fixed burst mode
226	 o mixed_burst: program the DMA to use the mixed burst mode
227	 o aal: Address-Aligned Beats
228	
229	---
230	
231	Below an example how the structures above are using on ST platforms.
232	
233	 static struct plat_stmmacenet_data stxYYY_ethernet_platform_data = {
234		.has_gmac = 0,
235		.enh_desc = 0,
236		.fix_mac_speed = stxYYY_ethernet_fix_mac_speed,
237					|
238					|-> to write an internal syscfg
239					|   on this platform when the
240					|   link speed changes from 10 to
241					|   100 and viceversa
242		.init = &stmmac_claim_resource,
243					|
244					|-> On ST SoC this calls own "PAD"
245					|   manager framework to claim
246					|   all the resources necessary
247					|   (GPIO ...). The .custom_cfg field
248					|   is used to pass a custom config.
249	};
250	
251	Below the usage of the stmmac_mdio_bus_data: on this SoC, in fact,
252	there are two MAC cores: one MAC is for MDIO Bus/PHY emulation
253	with fixed_link support.
254	
255	static struct stmmac_mdio_bus_data stmmac1_mdio_bus = {
256		.phy_reset = phy_reset;
257			|
258			|-> function to provide the phy_reset on this board
259		.phy_mask = 0,
260	};
261	
262	static struct fixed_phy_status stmmac0_fixed_phy_status = {
263		.link = 1,
264		.speed = 100,
265		.duplex = 1,
266	};
267	
268	During the board's device_init we can configure the first
269	MAC for fixed_link by calling:
270	  fixed_phy_add(PHY_POLL, 1, &stmmac0_fixed_phy_status, -1);
271	and the second one, with a real PHY device attached to the bus,
272	by using the stmmac_mdio_bus_data structure (to provide the id, the
273	reset procedure etc).
274	
275	Note that, starting from new chips, where it is available the HW capability
276	register, many configurations are discovered at run-time for example to
277	understand if EEE, HW csum, PTP, enhanced descriptor etc are actually
278	available. As strategy adopted in this driver, the information from the HW
279	capability register can replace what has been passed from the platform.
280	
281	4.10) Device-tree support.
282	
283	Please see the following document:
284		Documentation/devicetree/bindings/net/stmmac.txt
285	
286	4.11) This is a summary of the content of some relevant files:
287	 o stmmac_main.c: implements the main network device driver;
288	 o stmmac_mdio.c: provides MDIO functions;
289	 o stmmac_pci: this is the PCI driver;
290	 o stmmac_platform.c: this the platform driver (OF supported);
291	 o stmmac_ethtool.c: implements the ethtool support;
292	 o stmmac.h: private driver structure;
293	 o common.h: common definitions and VFTs;
294	 o mmc_core.c/mmc.h: Management MAC Counters;
295	 o stmmac_hwtstamp.c: HW timestamp support for PTP;
296	 o stmmac_ptp.c: PTP 1588 clock;
297	 o stmmac_pcs.h: Physical Coding Sublayer common implementation;
298	 o dwmac-<XXX>.c: these are for the platform glue-logic file; e.g. dwmac-sti.c
299	   for STMicroelectronics SoCs.
300	
301	- GMAC 3.x
302	 o descs.h: descriptor structure definitions;
303	 o dwmac1000_core.c: dwmac GiGa core functions;
304	 o dwmac1000_dma.c: dma functions for the GMAC chip;
305	 o dwmac1000.h: specific header file for the dwmac GiGa;
306	 o dwmac100_core: dwmac 100 core code;
307	 o dwmac100_dma.c: dma functions for the dwmac 100 chip;
308	 o dwmac1000.h: specific header file for the MAC;
309	 o dwmac_lib.c: generic DMA functions;
310	 o enh_desc.c: functions for handling enhanced descriptors;
311	 o norm_desc.c: functions for handling normal descriptors;
312	 o chain_mode.c/ring_mode.c:: functions to manage RING/CHAINED modes;
313	
314	- GMAC4.x generation
315	 o dwmac4_core.c: dwmac GMAC4.x core functions;
316	 o dwmac4_desc.c: functions for handling GMAC4.x descriptors;
317	 o dwmac4_descs.h: descriptor definitions;
318	 o dwmac4_dma.c: dma functions for the GMAC4.x chip;
319	 o dwmac4_dma.h: dma definitions for the GMAC4.x chip;
320	 o dwmac4.h: core definitions for the GMAC4.x chip;
321	 o dwmac4_lib.c: generic GMAC4.x functions;
322	
323	4.12) TSO support (GMAC4.x)
324	
325	TSO (Tcp Segmentation Offload) feature is supported by GMAC 4.x chip family.
326	When a packet is sent through TCP protocol, the TCP stack ensures that
327	the SKB provided to the low level driver (stmmac in our case) matches with
328	the maximum frame len (IP header + TCP header + payload <= 1500 bytes (for
329	MTU set to 1500)). It means that if an application using TCP want to send a
330	packet which will have a length (after adding headers) > 1514 the packet
331	will be split in several TCP packets: The data payload is split and headers
332	(TCP/IP ..) are added. It is done by software.
333	
334	When TSO is enabled, the TCP stack doesn't care about the maximum frame
335	length and provide SKB packet to stmmac as it is. The GMAC IP will have to
336	perform the segmentation by it self to match with maximum frame length.
337	
338	This feature can be enabled in device tree through "snps,tso" entry.
339	
340	5) Debug Information
341	
342	The driver exports many information i.e. internal statistics,
343	debug information, MAC and DMA registers etc.
344	
345	These can be read in several ways depending on the
346	type of the information actually needed.
347	
348	For example a user can be use the ethtool support
349	to get statistics: e.g. using: ethtool -S ethX
350	(that shows the Management counters (MMC) if supported)
351	or sees the MAC/DMA registers: e.g. using: ethtool -d ethX
352	
353	Compiling the Kernel with CONFIG_DEBUG_FS the driver will export the following
354	debugfs entries:
355	
356	/sys/kernel/debug/stmmaceth/descriptors_status
357	  To show the DMA TX/RX descriptor rings
358	
359	Developer can also use the "debug" module parameter to get further debug
360	information (please see: NETIF Msg Level).
361	
362	6) Energy Efficient Ethernet
363	
364	Energy Efficient Ethernet(EEE) enables IEEE 802.3 MAC sublayer along
365	with a family of Physical layer to operate in the Low power Idle(LPI)
366	mode. The EEE mode supports the IEEE 802.3 MAC operation at 100Mbps,
367	1000Mbps & 10Gbps.
368	
369	The LPI mode allows power saving by switching off parts of the
370	communication device functionality when there is no data to be
371	transmitted & received. The system on both the side of the link can
372	disable some functionalities & save power during the period of low-link
373	utilization. The MAC controls whether the system should enter or exit
374	the LPI mode & communicate this to PHY.
375	
376	As soon as the interface is opened, the driver verifies if the EEE can
377	be supported. This is done by looking at both the DMA HW capability
378	register and the PHY devices MCD registers.
379	To enter in Tx LPI mode the driver needs to have a software timer
380	that enable and disable the LPI mode when there is nothing to be
381	transmitted.
382	
383	7) Precision Time Protocol (PTP)
384	The driver supports the IEEE 1588-2002, Precision Time Protocol (PTP),
385	which enables precise synchronization of clocks in measurement and
386	control systems implemented with technologies such as network
387	communication.
388	
389	In addition to the basic timestamp features mentioned in IEEE 1588-2002
390	Timestamps, new GMAC cores support the advanced timestamp features.
391	IEEE 1588-2008 that can be enabled when configure the Kernel.
392	
393	8) SGMII/RGMII support
394	New GMAC devices provide own way to manage RGMII/SGMII.
395	This information is available at run-time by looking at the
396	HW capability register. This means that the stmmac can manage
397	auto-negotiation and link status w/o using the PHYLIB stuff.
398	In fact, the HW provides a subset of extended registers to
399	restart the ANE, verify Full/Half duplex mode and Speed.
400	Thanks to these registers, it is possible to look at the
401	Auto-negotiated Link Parter Ability.
Hide Line Numbers
About Kernel Documentation Linux Kernel Contact Linux Resources Linux Blog

Information is copyright its respective author. All material is available from the Linux Kernel Source distributed under a GPL License. This page is provided as a free service by mjmwired.net.