1FMC Device
   4Within the Linux bus framework, the FMC device is created and
   5registered by the carrier driver. For example, the PCI driver for the
   6SPEC card fills a data structure for each SPEC that it drives, and
   7registers an associated FMC device for each card.  The SVEC driver can
   8do exactly the same for the VME carrier (actually, it should do it
   9twice, because the SVEC carries two FMC mezzanines).  Similarly, an
  10Etherbone driver will be able to register its own FMC devices, offering
  11communication primitives through frame exchange.
  13The contents of the EEPROM within the FMC are used for identification
  14purposes, i.e. for matching the device with its own driver. For this
  15reason the device structure includes a complete copy of the EEPROM
  16(actually, the carrier driver may choose whether or not to return it -
  17for example we most likely won't have the whole EEPROM available for
  18Etherbone devices.
  20The following listing shows the current structure defining a device.
  21Please note that all the machinery is in place but some details may
  22still change in the future.  For this reason, there is a version field
  23at the beginning of the structure.  As usual, the minor number will
  24change for compatible changes (like a new flag) and the major number
  25will increase when an incompatible change happens (for example, a
  26change in layout of some fmc data structures).  Device writers should
  27just set it to the value FMC_VERSION, and be ready to get back -EINVAL
  28at registration time.
  30     struct fmc_device {
  31             unsigned long version;
  32             unsigned long flags;
  33             struct module *owner;           /* char device must pin it */
  34             struct fmc_fru_id id;           /* for EEPROM-based match */
  35             struct fmc_operations *op;      /* carrier-provided */
  36             int irq;                        /* according to host bus. 0 == none */
  37             int eeprom_len;                 /* Usually 8kB, may be less */
  38             int eeprom_addr;                /* 0x50, 0x52 etc */
  39             uint8_t *eeprom;                /* Full contents or leading part */
  40             char *carrier_name;             /* "SPEC" or similar, for special use */
  41             void *carrier_data;             /* "struct spec *" or equivalent */
  42             __iomem void *fpga_base;        /* May be NULL (Etherbone) */
  43             __iomem void *slot_base;        /* Set by the driver */
  44             struct fmc_device **devarray;   /* Allocated by the bus */
  45             int slot_id;                    /* Index in the slot array */
  46             int nr_slots;                   /* Number of slots in this carrier */
  47             unsigned long memlen;           /* Used for the char device */
  48             struct device dev;              /* For Linux use */
  49             struct device *hwdev;           /* The underlying hardware device */
  50             unsigned long sdbfs_entry;
  51             struct sdb_array *sdb;
  52             uint32_t device_id;             /* Filled by the device */
  53             char *mezzanine_name;           /* Defaults to ``fmc'' */
  54             void *mezzanine_data;
  55     };
  57The meaning of most fields is summarized in the code comment above.
  59The following fields must be filled by the carrier driver before
  62   * version: must be set to FMC_VERSION.
  64   * owner: set to MODULE_OWNER.
  66   * op: the operations to act on the device.
  68   * irq: number for the mezzanine; may be zero.
  70   * eeprom_len: length of the following array.
  72   * eeprom_addr: 0x50 for first mezzanine and so on.
  74   * eeprom: the full content of the I2C EEPROM.
  76   * carrier_name.
  78   * carrier_data: a unique pointer for the carrier.
  80   * fpga_base: the I/O memory address (may be NULL).
  82   * slot_id: the index of this slot (starting from zero).
  84   * memlen: if fpga_base is valid, the length of I/O memory.
  86   * hwdev: to be used in some dev_err() calls.
  88   * device_id: a slot-specific unique integer number.
  91Please note that the carrier should read its own EEPROM memory before
  92registering the device, as well as fill all other fields listed above.
  94The following fields should not be assigned, because they are filled
  95later by either the bus or the device driver:
  97   * flags.
  99   * fru_id: filled by the bus, parsing the eeprom.
 101   * slot_base: filled and used by the driver, if useful to it.
 103   * devarray: an array og all mezzanines driven by a singe FPGA.
 105   * nr_slots: set by the core at registration time.
 107   * dev: used by Linux.
 109   * sdb: FPGA contents, scanned according to driver's directions.
 111   * sdbfs_entry: SDB entry point in EEPROM: autodetected.
 113   * mezzanine_data: available for the driver.
 115   * mezzanine_name: filled by fmc-bus during identification.
 118Note: mezzanine_data may be redundant, because Linux offers the drvdata
 119approach, so the field may be removed in later versions of this bus
 122As I write this, she SPEC carrier is already completely functional in
 123the fmc-bus environment, and is a good reference to look at.
 126The API Offered by Carriers
 129The carrier provides a number of methods by means of the
 130`fmc_operations' structure, which currently is defined like this
 131(again, it is a moving target, please refer to the header rather than
 132this document):
 134     struct fmc_operations {
 135             uint32_t (*readl)(struct fmc_device *fmc, int offset);
 136             void (*writel)(struct fmc_device *fmc, uint32_t value, int offset);
 137             int (*reprogram)(struct fmc_device *f, struct fmc_driver *d, char *gw);
 138             int (*validate)(struct fmc_device *fmc, struct fmc_driver *drv);
 139             int (*irq_request)(struct fmc_device *fmc, irq_handler_t h,
 140                                char *name, int flags);
 141             void (*irq_ack)(struct fmc_device *fmc);
 142             int (*irq_free)(struct fmc_device *fmc);
 143             int (*gpio_config)(struct fmc_device *fmc, struct fmc_gpio *gpio,
 144                                int ngpio);
 145             int (*read_ee)(struct fmc_device *fmc, int pos, void *d, int l);
 146             int (*write_ee)(struct fmc_device *fmc, int pos, const void *d, int l);
 147     };
 149The individual methods perform the following tasks:
 153     These functions access FPGA registers by whatever means the
 154     carrier offers. They are not expected to fail, and most of the time
 155     they will just make a memory access to the host bus. If the
 156     carrier provides a fpga_base pointer, the driver may use direct
 157     access through that pointer. For this reason the header offers the
 158     inline functions fmc_readl and fmc_writel that access fpga_base if
 159     the respective method is NULL. A driver that wants to be portable
 160     and efficient should use fmc_readl and fmc_writel.  For Etherbone,
 161     or other non-local carriers, error-management is still to be
 162     defined.
 165     Module parameters are used to manage different applications for
 166     two or more boards of the same kind. Validation is based on the
 167     busid module parameter, if provided, and returns the matching
 168     index in the associated array. See *note Module Parameters:: in in
 169     doubt. If no match is found, `-ENOENT' is returned; if the user
 170     didn't pass `busid=', all devices will pass validation.  The value
 171     returned by the validate method can be used as index into other
 172     parameters (for example, some drivers use the `lm32=' parameter in
 173     this way). Such "generic parameters" are documented in *note
 174     Module Parameters::, below. The validate method is used by
 175     `fmc-trivial.ko', described in *note fmc-trivial::.
 178     The carrier enumerates FMC devices by loading a standard (or
 179     golden) FPGA binary that allows EEPROM access. Each driver, then,
 180     will need to reprogram the FPGA by calling this function.  If the
 181     name argument is NULL, the carrier should reprogram the golden
 182     binary. If the gateware name has been overridden through module
 183     parameters (in a carrier-specific way) the file loaded will match
 184     the parameters. Per-device gateware names can be specified using
 185     the `gateware=' parameter, see *note Module Parameters::.  Note:
 186     Clients should call rhe new helper, fmc_reprogram, which both
 187     calls this method and parse the SDB tree of the FPGA.
 192     Interrupt management is carrier-specific, so it is abstracted as
 193     operations. The interrupt number is listed in the device
 194     structure, and for the mezzanine driver the number is only
 195     informative.  The handler will receive the fmc pointer as dev_id;
 196     the flags argument is passed to the Linux request_irq function,
 197     but fmc-specific flags may be added in the future. You'll most
 198     likely want to pass the `IRQF_SHARED' flag.
 201     The method allows to configure a GPIO pin in the carrier, and read
 202     its current value if it is configured as input. See *note The GPIO
 203     Abstraction:: for details.
 207     Read or write the EEPROM. The functions are expected to be only
 208     called before reprogramming and the carrier should refuse them
 209     with `ENODEV' after reprogramming.  The offset is expected to be
 210     within 8kB (the current size), but addresses up to 1MB are
 211     reserved to fit bigger I2C devices in the future. Carriers may
 212     offer access to other internal flash memories using these same
 213     methods: for example the SPEC driver may define that its carrier
 214     I2C memory is seen at offset 1M and the internal SPI flash is seen
 215     at offset 16M.  This multiplexing of several flash memories in the
 216     same address space is is carrier-specific and should only be used
 217     by a driver that has verified the `carrier_name' field.
 221The GPIO Abstraction
 224Support for GPIO pins in the fmc-bus environment is not very
 225straightforward and deserves special discussion.
 227While the general idea of a carrier-independent driver seems to fly,
 228configuration of specific signals within the carrier needs at least
 229some knowledge of the carrier itself.  For this reason, the specific
 230driver can request to configure carrier-specific GPIO pins, numbered
 231from 0 to at most 4095.  Configuration is performed by passing a
 232pointer to an array of struct fmc_gpio items, as well as the length of
 233the array. This is the data structure:
 235        struct fmc_gpio {
 236                char *carrier_name;
 237                int gpio;
 238                int _gpio;      /* internal use by the carrier */
 239                int mode;       /* GPIOF_DIR_OUT etc, from <linux/gpio.h> */
 240                int irqmode;    /* IRQF_TRIGGER_LOW and so on */
 241        };
 243By specifying a carrier_name for each pin, the driver may access
 244different pins in different carriers.  The gpio_config method is
 245expected to return the number of pins successfully configured, ignoring
 246requests for other carriers. However, if no pin is configured (because
 247no structure at all refers to the current carrier_name), the operation
 248returns an error so the caller will know that it is running under a
 249yet-unsupported carrier.
 251So, for example, a driver that has been developed and tested on both
 252the SPEC and the SVEC may request configuration of two different GPIO
 253pins, and expect one such configuration to succeed - if none succeeds
 254it most likely means that the current carrier is a still-unknown one.
 256If, however, your GPIO pin has a specific known role, you can pass a
 257special number in the gpio field, using one of the following macros:
 259        #define FMC_GPIO_RAW(x)         (x)             /* 4096 of them */
 260        #define FMC_GPIO_IRQ(x)         ((x) + 0x1000)  /*  256 of them */
 261        #define FMC_GPIO_LED(x)         ((x) + 0x1100)  /*  256 of them */
 262        #define FMC_GPIO_KEY(x)         ((x) + 0x1200)  /*  256 of them */
 263        #define FMC_GPIO_TP(x)          ((x) + 0x1300)  /*  256 of them */
 264        #define FMC_GPIO_USER(x)        ((x) + 0x1400)  /*  256 of them */
 266Use of virtual GPIO numbers (anything but FMC_GPIO_RAW) is allowed
 267provided the carrier_name field in the data structure is left
 268unspecified (NULL). Each carrier is responsible for providing a mapping
 269between virtual and physical GPIO numbers. The carrier may then use the
 270_gpio field to cache the result of this mapping.
 272All carriers must map their I/O lines to the sets above starting from
 273zero.  The SPEC, for example, maps interrupt pins 0 and 1, and test
 274points 0 through 3 (even if the test points on the PCB are called
 277If, for example, a driver requires a free LED and a test point (for a
 278scope probe to be plugged at some point during development) it may ask
 279for FMC_GPIO_LED(0) and FMC_GPIO_TP(0). Each carrier will provide
 280suitable GPIO pins.  Clearly, the person running the drivers will know
 281the order used by the specific carrier driver in assigning leds and
 282testpoints, so to make a carrier-dependent use of the diagnostic tools.
 284In theory, some form of autodetection should be possible: a driver like
 285the wr-nic (which uses IRQ(1) on the SPEC card) should configure
 286IRQ(0), make a test with software-generated interrupts and configure
 287IRQ(1) if the test fails. This probing step should be used because even
 288if the wr-nic gateware is known to use IRQ1 on the SPEC, the driver
 289should be carrier-independent and thus use IRQ(0) as a first bet -
 290actually, the knowledge that IRQ0 may fail is carrier-dependent
 291information, but using it doesn't make the driver unsuitable for other
 294The return value of gpio_config is defined as follows:
 296   * If no pin in the array can be used by the carrier, `-ENODEV'.
 298   * If at least one virtual GPIO number cannot be mapped, `-ENOENT'.
 300   * On success, 0 or positive. The value returned is the number of
 301     high input bits (if no input is configured, the value for success
 302     is 0).
 304While I admit the procedure is not completely straightforward, it
 305allows configuration, input and output with a single carrier operation.
 306Given the typical use case of FMC devices, GPIO operations are not
 307expected to ever by in hot paths, and GPIO access so fare has only been
 308used to configure the interrupt pin, mode and polarity. Especially
 309reading inputs is not expected to be common. If your device has GPIO
 310capabilities in the hot path, you should consider using the kernel's
 311GPIO mechanisms.