Supported Standards

INF-8074

The INF-8084 standard was the original multiple source agreement (MSA) for SFP devices. It proposed the original series of management pages at i2c page 0xa0. This page contained up to 512 bytes, however, only the first 96 bytes are standardized. Bytes 97 to 127 are reserved for the vendor. The remaining bytes are reserved by the specification. The management page was subsequently adopted by SFP+ devices.

SFF-8472

The SFF-8472 standard extended the original SFP MSA. This standard added a second i2c page at 0xa2, while maintaining the original page at 0xa0. The page at 0xa0 is now explicitly 256 bytes. The page at 0xa2 is also 256 bytes. This standard was also adopted for all SFP28 parts, which are commonly used in transceivers for 25 Gb/s Ethernet.

SFF-8436

The SFF-8436 standard was developed for QSFP+ transceivers, which involve the bonding of 4 SFP+ links. QSFP+ is commonly used in the transceivers for 40 Gb/s Ethernet. This standard uses i2c page 0xa0 for read-only identification purposes. The lower half of the page is used for control, while the upper 128 bytes is similar to the INF-8084 and SFF-8472 standards.

SFF-8636

The SFF-8636 standard is a common management standard which is shared between both SAS and QSFP+ 28 Gb/s transceivers. The latter transceiver is commonly found in 100 Gb/s Ethernet. The transceiver's memory map is similar to that found in the SFF-8436 specification. The identification information is found in the upper 128 bytes of page 0xa0, while the lower part of the page is used for control, among other purposes.

The following table summarizes the above information.

MAC Capability Structure

When the device driver's mc_getcapab(9E) function entry point is called with the capability requested set to MAC_CAPAB_TRANSCEIVER, then the value of the capability structure is the following structure:

typedef struct mac_capab_transceiver {
	uint_t	mct_flags;
	uint_t	mct_ntransceivers;
	int	(*mct_info)(void *driver, uint_t id,
		    mac_transceiver_info_t *infop),
	int	(*mct_read)(void *driver, uint_t id, uint_t page,
		    void *buf, size_t nbytes, off_t offset,
		    size_t *nread)
} mac_capab_transceiver_t;

If the device driver supports the MAC_CAPAB_TRANSCEIVER capability, it should fill in this structure, based on the following rules:

mct_flags

The mct_flags member is used to negotiate extensions with the driver. MAC will set the value of mct_flags to include all of the currently known extensions. The driver should intersect this list with the set that they actually support. At this time, no such features are defined and the driver should set the member to 0.

mct_ntransceivers

The value of mct_ntransceivers indicates the number of transceivers present in the device. For most devices, it is expected that this value will be set to one. However, some devices do support multiple transceivers and PHYs that show up behind a single logical MAC.

It is expected that this value will not change across the lifetime of the device being attached. It is important to remember that this represents the total possible number of transceivers in the device, not how many are currently present and powered on.

The number of transceivers will influence the id argument used in the mct_info() and mct_read() entry points. The transceiver IDs will start at zero and go to the value of mct_ntransceivers - 1. It is up to the driver to keep the mapping between actual transceivers and the transceiver identifiers consistent.

mct_info

The mct_info() entry point is used to set basic information about the transceiver. This entry point is required. If the device driver cannot implement this entry point, then it should not indicate that it supports the capability.

The mct_info() entry point should fill in information about the transceiver with an identifier of id. See the description above of mct_ntransceivers for more information on how the IDs are determined.

The driver should then proceed to fill in basic information by calling the functions described in the section Information Functions. After successfully calling all of the functions, the driver should return 0. Otherwise, it should return the appropriate error number. For a full list of error numbers, see Intro(2). Common values are:

EINVAL

The transceiver identifier id was invalid.

ENOTSUP

This instance of the devices does not support a transceiver. For example, a device which sometimes has copper PHYs and therefore this instance does not have any PHYs.

EIO

An error occurred while trying to read device registers. For example, an FM-aware device had an error.

mct_read

The mct_read() function is used to read information from a transceiver's i2c bus. The mct_read() entry point is an optional entry point.

The transceiver should first check the value of id, which indicates which transceiver information is being requested. See the description above of mct_ntransceivers for more information on how the IDs are determined.

The driver should try to read up to nbytes of data from the i2c bus at page page. The driver should start reading at offset offset. Finally, it should update the value in nread with the number of bytes written to the buffer buf.

If for some reason the driver cannot read all of the requested bytes, that is acceptable. Instead it should perform a short read. This may occur because the transceiver does not allow reads at a requested region or the region is shorter than is common for most devices.

Upon successful completion, the driver should ensure that nread has been updated and then return 0. Otherwise, the driver should return the appropriate error number. For a full list of error numbers, see Intro(2). Common values are:

EINVAL

The value of id represented an invalid transceiver identifier. The transceiver i2c page page is not valid for this type of device. The value of offset is beyond the range supported for this page.

EIO

An error occurred while trying to read the device i2c pages.

Transceiver Information Functions

The mct_info() entry point is the primary required entry point for a device driver which supports this capability. The information structure is opaque to the device driver. Instead, a series of informational functions is available to the device driver to call on the transceiver. The device drivers should try to call and fill in as many of these as possible. There are two different properties that a driver can set:

1. Whether the transceiver is present.
2. Whether the transceiver is usable.

To set whether or not the transceiver is present, the driver should call mac_transceiver_info_set_present(9F). This is used to indicate whether the transceiver is plugged in or not. If the transceiver is a part of the NIC, then this function should always be called with the value set to B_TRUE.

Finally, the driver has the ability to provide information about whether or not the transceiver is usable or not. A transceiver may be present, but not usable, if the hardware and firmware support a limited number of transceivers. To set this information, the driver should call mac_transceiver_info_set_usable(9F). If the transceiver is not present, then the driver should not call this function.

Opaque Transceivers

Some devices abstract the nature of the transceiver and do not allow direct access to the transceiver. In this case, if the device driver still has access to enough information to know if the transceiver is at least present, then it should still implement the mct_info() entry point.

Locking and Data Access

Calls to get information about the transceivers may come at the same time as general I/O requests to the device to send or receive data. The driver should make sure that reading data from the i2c bus of the transceiver does not interfere with the device's functionality in this regard. Different locks should be used.

On some devices, reading from the transceiver's i2c bus might cause a disruption of service to the device. For example, on some devices a phy reset may be required or come about as a side effect of trying to read the device. If any kind of disruption would be caused, then the driver must not implement the mct_read entry point.