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authorDavid S. Miller <davem@davemloft.net>2010-04-11 17:53:53 -0400
committerDavid S. Miller <davem@davemloft.net>2010-04-11 17:53:53 -0400
commit871039f02f8ec4ab2e5e9010718caa8e085786f1 (patch)
treef0d2b3127fc48c862967d68c46c2d46668137515 /Documentation/networking
parente4077e018b5ead3de9951fc01d8bf12eeeeeefed (diff)
parent4a1032faac94ebbf647460ae3e06fc21146eb280 (diff)
Merge branch 'master' of master.kernel.org:/pub/scm/linux/kernel/git/davem/net-2.6
Conflicts: drivers/net/stmmac/stmmac_main.c drivers/net/wireless/wl12xx/wl1271_cmd.c drivers/net/wireless/wl12xx/wl1271_main.c drivers/net/wireless/wl12xx/wl1271_spi.c net/core/ethtool.c net/mac80211/scan.c
Diffstat (limited to 'Documentation/networking')
-rw-r--r--Documentation/networking/timestamping.txt76
1 files changed, 46 insertions, 30 deletions
diff --git a/Documentation/networking/timestamping.txt b/Documentation/networking/timestamping.txt
index 0e58b4539176..e8c8f4f06c67 100644
--- a/Documentation/networking/timestamping.txt
+++ b/Documentation/networking/timestamping.txt
@@ -41,11 +41,12 @@ SOF_TIMESTAMPING_SOFTWARE: return system time stamp generated in
41SOF_TIMESTAMPING_TX/RX determine how time stamps are generated. 41SOF_TIMESTAMPING_TX/RX determine how time stamps are generated.
42SOF_TIMESTAMPING_RAW/SYS determine how they are reported in the 42SOF_TIMESTAMPING_RAW/SYS determine how they are reported in the
43following control message: 43following control message:
44 struct scm_timestamping { 44
45 struct timespec systime; 45struct scm_timestamping {
46 struct timespec hwtimetrans; 46 struct timespec systime;
47 struct timespec hwtimeraw; 47 struct timespec hwtimetrans;
48 }; 48 struct timespec hwtimeraw;
49};
49 50
50recvmsg() can be used to get this control message for regular incoming 51recvmsg() can be used to get this control message for regular incoming
51packets. For send time stamps the outgoing packet is looped back to 52packets. For send time stamps the outgoing packet is looped back to
@@ -87,12 +88,13 @@ by the network device and will be empty without that support.
87SIOCSHWTSTAMP: 88SIOCSHWTSTAMP:
88 89
89Hardware time stamping must also be initialized for each device driver 90Hardware time stamping must also be initialized for each device driver
90that is expected to do hardware time stamping. The parameter is: 91that is expected to do hardware time stamping. The parameter is defined in
92/include/linux/net_tstamp.h as:
91 93
92struct hwtstamp_config { 94struct hwtstamp_config {
93 int flags; /* no flags defined right now, must be zero */ 95 int flags; /* no flags defined right now, must be zero */
94 int tx_type; /* HWTSTAMP_TX_* */ 96 int tx_type; /* HWTSTAMP_TX_* */
95 int rx_filter; /* HWTSTAMP_FILTER_* */ 97 int rx_filter; /* HWTSTAMP_FILTER_* */
96}; 98};
97 99
98Desired behavior is passed into the kernel and to a specific device by 100Desired behavior is passed into the kernel and to a specific device by
@@ -139,42 +141,56 @@ enum {
139 /* time stamp any incoming packet */ 141 /* time stamp any incoming packet */
140 HWTSTAMP_FILTER_ALL, 142 HWTSTAMP_FILTER_ALL,
141 143
142 /* return value: time stamp all packets requested plus some others */ 144 /* return value: time stamp all packets requested plus some others */
143 HWTSTAMP_FILTER_SOME, 145 HWTSTAMP_FILTER_SOME,
144 146
145 /* PTP v1, UDP, any kind of event packet */ 147 /* PTP v1, UDP, any kind of event packet */
146 HWTSTAMP_FILTER_PTP_V1_L4_EVENT, 148 HWTSTAMP_FILTER_PTP_V1_L4_EVENT,
147 149
148 ... 150 /* for the complete list of values, please check
151 * the include file /include/linux/net_tstamp.h
152 */
149}; 153};
150 154
151 155
152DEVICE IMPLEMENTATION 156DEVICE IMPLEMENTATION
153 157
154A driver which supports hardware time stamping must support the 158A driver which supports hardware time stamping must support the
155SIOCSHWTSTAMP ioctl. Time stamps for received packets must be stored 159SIOCSHWTSTAMP ioctl and update the supplied struct hwtstamp_config with
156in the skb with skb_hwtstamp_set(). 160the actual values as described in the section on SIOCSHWTSTAMP.
161
162Time stamps for received packets must be stored in the skb. To get a pointer
163to the shared time stamp structure of the skb call skb_hwtstamps(). Then
164set the time stamps in the structure:
165
166struct skb_shared_hwtstamps {
167 /* hardware time stamp transformed into duration
168 * since arbitrary point in time
169 */
170 ktime_t hwtstamp;
171 ktime_t syststamp; /* hwtstamp transformed to system time base */
172};
157 173
158Time stamps for outgoing packets are to be generated as follows: 174Time stamps for outgoing packets are to be generated as follows:
159- In hard_start_xmit(), check if skb_hwtstamp_check_tx_hardware() 175- In hard_start_xmit(), check if skb_tx(skb)->hardware is set no-zero.
160 returns non-zero. If yes, then the driver is expected 176 If yes, then the driver is expected to do hardware time stamping.
161 to do hardware time stamping.
162- If this is possible for the skb and requested, then declare 177- If this is possible for the skb and requested, then declare
163 that the driver is doing the time stamping by calling 178 that the driver is doing the time stamping by setting the field
164 skb_hwtstamp_tx_in_progress(). A driver not supporting 179 skb_tx(skb)->in_progress non-zero. You might want to keep a pointer
165 hardware time stamping doesn't do that. A driver must never 180 to the associated skb for the next step and not free the skb. A driver
166 touch sk_buff::tstamp! It is used to store how time stamping 181 not supporting hardware time stamping doesn't do that. A driver must
167 for an outgoing packets is to be done. 182 never touch sk_buff::tstamp! It is used to store software generated
183 time stamps by the network subsystem.
168- As soon as the driver has sent the packet and/or obtained a 184- As soon as the driver has sent the packet and/or obtained a
169 hardware time stamp for it, it passes the time stamp back by 185 hardware time stamp for it, it passes the time stamp back by
170 calling skb_hwtstamp_tx() with the original skb, the raw 186 calling skb_hwtstamp_tx() with the original skb, the raw
171 hardware time stamp and a handle to the device (necessary 187 hardware time stamp. skb_hwtstamp_tx() clones the original skb and
172 to convert the hardware time stamp to system time). If obtaining 188 adds the timestamps, therefore the original skb has to be freed now.
173 the hardware time stamp somehow fails, then the driver should 189 If obtaining the hardware time stamp somehow fails, then the driver
174 not fall back to software time stamping. The rationale is that 190 should not fall back to software time stamping. The rationale is that
175 this would occur at a later time in the processing pipeline 191 this would occur at a later time in the processing pipeline than other
176 than other software time stamping and therefore could lead 192 software time stamping and therefore could lead to unexpected deltas
177 to unexpected deltas between time stamps. 193 between time stamps.
178- If the driver did not call skb_hwtstamp_tx_in_progress(), then 194- If the driver did not call set skb_tx(skb)->in_progress, then
179 dev_hard_start_xmit() checks whether software time stamping 195 dev_hard_start_xmit() checks whether software time stamping
180 is wanted as fallback and potentially generates the time stamp. 196 is wanted as fallback and potentially generates the time stamp.