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| -rw-r--r-- | Documentation/fmc/mezzanine.txt | 123 |
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diff --git a/Documentation/fmc/mezzanine.txt b/Documentation/fmc/mezzanine.txt new file mode 100644 index 000000000..87910dbfc --- /dev/null +++ b/Documentation/fmc/mezzanine.txt @@ -0,0 +1,123 @@ +FMC Driver +********** + +An FMC driver is concerned with the specific mezzanine and associated +gateware. As such, it is expected to be independent of the carrier +being used: it will perform I/O accesses only by means of +carrier-provided functions. + +The matching between device and driver is based on the content of the +EEPROM (as mandated by the FMC standard) or by the actual cores +configured in the FPGA; the latter technique is used when the FPGA is +already programmed when the device is registered to the bus core. + +In some special cases it is possible for a driver to directly access +FPGA registers, by means of the `fpga_base' field of the device +structure. This may be needed for high-bandwidth peripherals like fast +ADC cards. If the device module registered a remote device (for example +by means of Etherbone), the `fpga_base' pointer will be NULL. +Therefore, drivers must be ready to deal with NULL base pointers, and +fail gracefully. Most driver, however, are not expected to access the +pointer directly but run fmc_readl and fmc_writel instead, which will +work in any case. + +In even more special cases, the driver may access carrier-specific +functionality: the `carrier_name' string allows the driver to check +which is the current carrier and make use of the `carrier_data' +pointer. We chose to use carrier names rather than numeric identifiers +for greater flexibility, but also to avoid a central registry within +the `fmc.h' file - we hope other users will exploit our framework with +their own carriers. An example use of carrier names is in GPIO setup +(see *note The GPIO Abstraction::), although the name match is not +expected to be performed by the driver. If you depend on specific +carriers, please check the carrier name and fail gracefully if your +driver finds it is running in a yet-unknown-to-it environment. + + +ID Table +======== + +Like most other Linux drivers, and FMC driver must list all the devices +which it is able to drive. This is usually done by means of a device +table, but in FMC we can match hardware based either on the contents of +their EEPROM or on the actual FPGA cores that can be enumerated. +Therefore, we have two tables of identifiers. + +Matching of FRU information depends on two names, the manufacturer (or +vendor) and the device (see *note FMC Identification::); for +flexibility during production (i.e. before writing to the EEPROM) the +bus supports a catch-all driver that specifies NULL strings. For this +reason, the table is specified as pointer-and-length, not a a +null-terminated array - the entry with NULL names can be a valid entry. + +Matching on FPGA cores depends on two numeric fields: the 64-bit vendor +number and the 32-bit device number. Support for matching based on +class is not yet implemented. Each device is expected to be uniquely +identified by an array of cores (it matches if all of the cores are +instantiated), and for consistency the list is passed as +pointer-and-length. Several similar devices can be driven by the same +driver, and thus the driver specifies and array of such arrays. + +The complete set of involved data structures is thus the following: + + struct fmc_fru_id { char *manufacturer; char *product_name; }; + struct fmc_sdb_one_id { uint64_t vendor; uint32_t device; }; + struct fmc_sdb_id { struct fmc_sdb_one_id *cores; int cores_nr; }; + + struct fmc_device_id { + struct fmc_fru_id *fru_id; int fru_id_nr; + struct fmc_sdb_id *sdb_id; int sdb_id_nr; + }; + +A better reference, with full explanation, is the <linux/fmc.h> header. + + +Module Parameters +================= + +Most of the FMC drivers need the same set of kernel parameters. This +package includes support to implement common parameters by means of +fields in the `fmc_driver' structure and simple macro definitions. + +The parameters are carrier-specific, in that they rely on the busid +concept, that varies among carriers. For the SPEC, the identifier is a +PCI bus and devfn number, 16 bits wide in total; drivers for other +carriers will most likely offer something similar but not identical, +and some code duplication is unavoidable. + +This is the list of parameters that are common to several modules to +see how they are actually used, please look at spec-trivial.c. + +`busid=' + This is an array of integers, listing carrier-specific + identification numbers. For PIC, for example, `0x0400' represents + bus 4, slot 0. If any such ID is specified, the driver will only + accept to drive cards that appear in the list (even if the FMC ID + matches). This is accomplished by the validate carrier method. + +`gateware=' + The argument is an array of strings. If no busid= is specified, + the first string of gateware= is used for all cards; otherwise the + identifiers and gateware names are paired one by one, in the order + specified. + +`show_sdb=' + For modules supporting it, this parameter asks to show the SDB + internal structure by means of kernel messages. It is disabled by + default because those lines tend to hide more important messages, + if you look at the system console while loading the drivers. + Note: the parameter is being obsoleted, because fmc.ko itself now + supports dump_sdb= that applies to every client driver. + + +For example, if you are using the trivial driver to load two different +gateware files to two different cards, you can use the following +parameters to load different binaries to the cards, after looking up +the PCI identifiers. This has been tested with a SPEC carrier. + + insmod fmc-trivial.ko \ + busid=0x0200,0x0400 \ + gateware=fmc/fine-delay.bin,fmc/simple-dio.bin + +Please note that not all sub-modules support all of those parameters. +You can use modinfo to check what is supported by each module. |