Manual browser: wdc(9)

WDC(9) Kernel Developer's Manual WDC(9)


wdcmachine-independent IDE/ATAPI driver


#include <dev/ata/atavar.h>
#include <sys/dev/ic/wdcvar.h>

wdcprobe(struct channel_softc * chp);

wdcattach(struct channel_softc * chp);


The wdc driver provides the machine independent core functions for driving IDE devices. IDE devices-specific drivers (wd(4) or atapibus(4)) will use services provided by wdc.

The machine-dependent bus front-end provides informations to wdc with the wdc_softc and channel_softc structures. The first one defines global controller properties, and the second contains per-channel informations. wdc returns informations about the attached devices in the ata_drive_datas structure.

struct wdc_softc { /* Per controller state */ 
        struct device sc_dev; 
        int           cap; 
#define WDC_CAPABILITY_DATA16 0x0001 
#define WDC_CAPABILITY_DATA32 0x0002 
#define WDC_CAPABILITY_MODE   0x0004 
#define WDC_CAPABILITY_DMA    0x0008 
#define WDC_CAPABILITY_UDMA   0x0010 
#define WDC_CAPABILITY_NOIRQ  0x1000 
#define WDC_CAPABILITY_SELECT  0x2000 
        uint8_t      pio_mode; 
        uint8_t      dma_mode; 
        int nchannels; 
        struct channel_softc *channels; 
        void            *dma_arg; 
        int            (*dma_init)(void *, int, int, void *, size_t, int); 
        void           (*dma_start)(void *, int, int, int); 
        int            (*dma_finish)(void *, int, int, int); 
#define WDC_DMA_READ 0x01 
#define WDC_DMA_POLL 0x02 
        int            (*claim_hw)(void *, int); 
        void            (*free_hw)(void *); 
struct channel_softc { /* Per channel data */ 
        int channel; 
        struct wdc_softc *wdc; 
        bus_space_tag_t       cmd_iot; 
        bus_space_handle_t    cmd_ioh; 
        bus_space_tag_t       ctl_iot; 
        bus_space_handle_t    ctl_ioh; 
        bus_space_tag_t       data32iot; 
        bus_space_handle_t    data32ioh; 
        int ch_flags; 
#define WDCF_ACTIVE   0x01 
#define WDCF_IRQ_WAIT 0x10 
        uint8_t ch_status; 
        uint8_t ch_error; 
        struct ata_drive_datas ch_drive[2]; 
        struct channel_queue *ch_queue; 
struct ata_drive_datas { 
    uint8_t drive; 
    uint8_t drive_flags; 
#define DRIVE_ATA   0x01 
#define DRIVE_ATAPI 0x02 
#define DRIVE_CAP32 0x04 
#define DRIVE_DMA   0x08 
#define DRIVE_UDMA  0x10 
#define DRIVE_MODE 0x20 
    uint8_t PIO_mode; 
    uint8_t DMA_mode; 
    uint8_t UDMA_mode; 
    uint8_t state; 
    struct device *drv_softc; 
    void* chnl_softc; 

The bus front-end needs to fill in the following elements of wdc_softc:

supports one or more of the WDC_CAPABILITY flags
number of channels supported by this controller
array of struct channel_softc of size nchannels properly initialised
The following elements are optional:

The WDC_CAPABILITY_DATA16 and WDC_CAPABILITY_DATA32 flags informs wdc whether the controller supports 16- or 32-bit I/O accesses on the data port. If both are set, a test will be done for each drive using the ATA or ATAPI IDENTIFY command, to automatically select the working mode.

The WDC_CAPABILITY_DMA and WDC_CAPABILITY_UDMA flags are set for controllers supporting the DMA and Ultra-DMA modes. The bus front-end needs to provide the dma_init(), dma_start() and dma_finish() functions. dma_init() is called just before issuing a DMA command to the IDE device. The arguments are, respectively: dma_arg, the channel number, the drive number on this channel, the virtual address of the DMA buffer, the size of the transfer, and the WDC_DMA flags. dma_start() is called just after issuing a DMA command to the IDE device. The arguments are, respectively: dma_arg, the channel number, the drive number on this channel, and the WDC_DMA flags. dma_finish() is called once the transfer is complete. The arguments are, respectively: dma_arg, the channel number, the drive number on this channel, and the WDC_DMA flags. WDC_DMA_READ indicates the direction of the data transfer, and WDC_DMA_POLL indicates if the transfer will use (or used) interrupts.

The WDC_CAPABILITY_MODE flag means that the bus front-end can program the PIO and DMA modes, so wdc needs to provide back the supported modes for each drive, and set the drives modes. The pio_mode and dma_mode needs to be set to the highest PIO and DMA mode supported. If WDC_CAPABILITY_UDMA is set, then dma_mode must be set to the highest Ultra-DMA mode supported. If WDC_CAPABILITY_MODE is not set, wdc will not attempt to change the current drive's settings, assuming the host's firmware has done it right.

The WDC_CAPABILITY_HWLOCK flag is set for controllers needing hardware looking before accessing the I/O ports. If this flag is set, the bus front-end needs to provide the claim_hw() and free_hw() functions. claim_hw() will be called when the driver wants to access the controller ports. The second parameter is set to 1 when it is possible to sleep waiting for the lock, 0 otherwise. It should return 1 when access has been granted, 0 otherwise. When access has not been granted and sleep is not allowed, the bus front-end shall call wdcrestart() with the first argument passed to claim_hw() as argument. This arguments will also be the one passed to free_hw(). This function is called once the transfer is complete, so that the lock can be released.

Accesses to the data port are done by using the bus_space stream functions, unless the WDC_CAPABILITY_ATA_NOSTREAM or WDC_CAPABILITY_ATAPI_NOSTREAM flags are set. This should not be used, unless the data bus is not wired properly (which seems common on big-endian systems), and byte-order needs to be preserved for compatibility with the host's firmware. Also note that the IDE bus is a little-endian bus, so the bus_space functions used for the bus_space tag passed in the channel_softc have to do the appropriate byte-swapping for big-endian systems.

WDC_CAPABILITY_NO_EXTRA_RESETS avoid the controller reset at the end of the disks probe. This reset is needed for some controllers, but causes problems with some others.

WDC_CAPABILITY_NOIRQ tells the driver that this controller doesn't have its interrupt lines wired up usefully, so it should always use polled transfers.

The bus front-end needs to fill in the following elements of channel_softc:

The channel number on the controller
A pointer to the controller's wdc_softc
cmd_iot, cmd_ioh
Bus-space tag and handle for access to the command block registers (which includes the 16-bit data port)
ctl_iot, ctl_ioh
Bus-space tag and handle for access to the control block registers
A pointer to a struct channel_queue. This will hold the queues of outstanding commands for this controller.
The following elements are optional:
data32iot, data32ioh
Bus-space tag and handle for 32-bit data accesses. Only needed if WDC_CAPABILITY_DATA32 is set in the controller's wdc_softc.

ch_queue can point to a common struct channel_queue if the controller doesn't support concurrent access to its different channels. If all channels are independent, it is recommended that each channel has its own ch_queue (for better performance).

The bus-specific front-end can use the wdcprobe() function, with a properly initialised struct channel_softc as argument ( wdc can be set to NULL. This allows wdcprobe() to be easily used in bus front-end probe functions). This function will return an integer where bit 0 will be set if the master device has been found, and 1 if the slave device has been found.

The bus-specific attach function has to call wdcattach() for each channel, with a pointer to a properly initialised channel softc as argument. This will probe devices attached to the IDE channel and attach them. Once this function returns, the ch_drive array of the channel_softc will contain the drive's capabilities. This can be used to properly initialise the controller's mode, or disable a channel without drives.

The elements of interest in ata_drive_datas for a bus front-end are:

The drive number
Flags indicating the drive capabilities. A null drive_flags indicate either that no drive is here, or that no driver was found for this device.
PIO_mode, DMA_mode, UDMA_mode
the highest supported modes for this drive compatible with the controller's capabilities. Needs to be reset to the mode to use by the drive, if known.
A pointer to the drive's softc. Can be used to print the drive's name.

drive_flags handles the following flags:

Gives the drive type, if any. The shortcut DRIVE can be used to just test the presence/absence of a drive.
This drive works with 32-bit data I/O.
This drive supports DMA.
This drive supports Ultra-DMA.
This drive properly reported its PIO and DMA mode.

Once the controller has been initialised, it has to reset the DRIVE_DMA and DRIVE_UDMA, as well as the values of PIO_mode, DMA_mode and UDMA_mode if the modes to be used are not highest ones supported by the drive.


The wdc core functions are implemented in sys/dev/ic/wdc.c. Low-level ATA and ATAPI support is provided by sys/dev/ata_wdc.c and sys/dev/scsipi/atapi_wdc.c respectively.

An example of a simple bus front-end can be found in sys/dev/isapnp/wdc_isapnp.c. A more complex one, with multiple channels and bus-master DMA support is sys/dev/pci/pciide.c. sys/arch/atari/dev/wdc_mb.c makes use of hardware locking, and also provides an example of bus-front end for a big-endian system, which needs byte-swapping bus_space functions.


wdc(4), bus_space(9)
April 18, 2010 NetBSD 7.0