doc/en_US.ISO8859-1/books/developers-handbook/pci/chapter.sgml

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<chapter id="pci">
  <title>PCI Devices</title>

  <para>This chapter will talk about the FreeBSD mechanisms for
    writing a device driver for a device on a PCI bus.</para>

  <sect1 id="pci-probe">
    <title>Probe and Attach</title>

    <para>Information here about how the PCI bus code iterates through
      the unattached devices and see if a newly loaded kld will attach
      to any of them.</para>

<programlisting>/*
 * Simple KLD to play with the PCI functions.
 *
 * Murray Stokely
 */

#define MIN(a,b) (((a) < (b)) ? (a) : (b))

#include &lt;sys/types.h&gt;
#include &lt;sys/module.h&gt;
#include &lt;sys/systm.h&gt;  /* uprintf */ 
#include &lt;sys/errno.h&gt;
#include &lt;sys/param.h&gt;  /* defines used in kernel.h */
#include &lt;sys/kernel.h&gt; /* types used in module initialization */
#include &lt;sys/conf.h&gt;   /* cdevsw struct */
#include &lt;sys/uio.h&gt;    /* uio struct */
#include &lt;sys/malloc.h&gt;
#include &lt;sys/bus.h&gt;	/* structs, prototypes for pci bus stuff */

#include &lt;pci/pcivar.h&gt; /* For get_pci macros! */

/* Function prototypes */
d_open_t      mypci_open;
d_close_t     mypci_close;
d_read_t      mypci_read;
d_write_t     mypci_write;

/* Character device entry points */

static struct cdevsw mypci_cdevsw = {
  mypci_open,
  mypci_close,
  mypci_read,
  mypci_write,
  noioctl,
  nopoll,
  nommap,
  nostrategy,
  "mypci",
  36,                   /* reserved for lkms - /usr/src/sys/conf/majors */
  nodump,
  nopsize,
  D_TTY,
  -1
};

/* vars */
static dev_t sdev;

/* We're more interested in probe/attach than with
   open/close/read/write at this point */

int 
mypci_open(dev_t dev, int oflags, int devtype, struct proc *p)
{
  int err = 0;

  uprintf("Opened device \"mypci\" successfully.\n");
  return(err);
}

int 
mypci_close(dev_t dev, int fflag, int devtype, struct proc *p)
{
  int err=0;

  uprintf("Closing device \"mypci.\"\n"); 
  return(err);
} 

int
mypci_read(dev_t dev, struct uio *uio, int ioflag)
{
  int err = 0;

  uprintf("mypci read!\n");
  return err;
}

int
mypci_write(dev_t dev, struct uio *uio, int ioflag)
{
  int err = 0;

  uprintf("mypci write!\n");
  return(err);
}

/* PCI Support Functions */

/*
 * Return identification string if this is device is ours.
 */
static int
mypci_probe(device_t dev)
{
  uprintf("MyPCI Probe\n"
	  "Vendor ID : 0x%x\n"
	  "Device ID : 0x%x\n",pci_get_vendor(dev),pci_get_device(dev));

  if (pci_get_vendor(dev) == 0x11c1) {
    uprintf("We've got the Winmodem, probe successful!\n");
    return 0;
  }

  return ENXIO;
}

/* Attach function is only called if the probe is successful */

static int
mypci_attach(device_t dev)
{
  uprintf("MyPCI Attach for : deviceID : 0x%x\n",pci_get_vendor(dev));
  sdev = make_dev(<literal>&</literal>mypci_cdevsw,
		  0,
		  UID_ROOT,
		  GID_WHEEL,
		  0600,
		  "mypci");
  uprintf("Mypci device loaded.\n");
  return ENXIO;
}

/* Detach device. */

static int
mypci_detach(device_t dev)
{
  uprintf("Mypci detach!\n");
  return 0;
}

/* Called during system shutdown after sync. */

static int
mypci_shutdown(device_t dev)
{
  uprintf("Mypci shutdown!\n");
  return 0;
}

/*
 * Device suspend routine.  
 */
static int
mypci_suspend(device_t dev)
{
  uprintf("Mypci suspend!\n");
  return 0;
}

/*
 * Device resume routine.
 */

static int
mypci_resume(device_t dev)
{
  uprintf("Mypci resume!\n");
  return 0;
}

static device_method_t mypci_methods[] = {
	/* Device interface */
	DEVMETHOD(device_probe,		mypci_probe),
	DEVMETHOD(device_attach,	mypci_attach),
	DEVMETHOD(device_detach,	mypci_detach),
	DEVMETHOD(device_shutdown,	mypci_shutdown),
	DEVMETHOD(device_suspend,	mypci_suspend),
	DEVMETHOD(device_resume,	mypci_resume),

	{ 0, 0 }
};

static driver_t mypci_driver = {
	"mypci",
	mypci_methods,
	0,
	/*	sizeof(struct mypci_softc), */
};

static devclass_t mypci_devclass;

DRIVER_MODULE(mypci, pci, mypci_driver, mypci_devclass, 0, 0);</programlisting>
      
    <para>Additional Resources
    <itemizedlist>
      <listitem><simpara><ulink url="http://www.pcisig.org/">PCI
	Special Interest Group</ulink></simpara></listitem>

      <listitem><simpara>PCI System Architecture, Fourth Edition by
	Tom Shanley, et al.</simpara></listitem>

    </itemizedlist>
    </para>
  </sect1>

  <sect1 id="pci-bus">
    <title>Bus Resources</title>

    <para>FreeBSD provides an object-oriented mechanism for requesting
      resources from a parent bus.  Almost all devices will be a child
      member of some sort of bus (PCI, ISA, USB, SCSI, etc) and these
      devices need to acquire resources from their parent bus (such as
      memory segments, interrupt lines, or DMA channels).</para>

    <sect2>
      <title>Base Address Registers</title>

      <para>To do anything particularly useful with a PCI device you
      will need to obtain the <emphasis>Base Address
      Registers</emphasis> (BARs) from the PCI Configuration space.
      The PCI-specific details of obtaining the BAR are abstracted in
      the <function>bus_alloc_resource()</function> function.</para>

      <para>For example, a typical driver might have something similar
      to this in the <function>attach()</function> function:</para>

<programlisting>    sc->bar0id = 0x10;
    sc->bar0res = bus_alloc_resource(dev, SYS_RES_MEMORY, &amp;(sc->bar0id),
				  0, ~0, 1, RF_ACTIVE);
    if (sc->bar0res == NULL) {
        uprintf("Memory allocation of PCI base register 0 failed!\n");
        error = ENXIO;
        goto fail1;
    }

    sc->bar1id = 0x14;
    sc->bar1res = bus_alloc_resource(dev, SYS_RES_MEMORY, &amp;(sc->bar1id),
				  0, ~0, 1, RF_ACTIVE);
    if (sc->bar1res == NULL) {
        uprintf("Memory allocation of PCI base register 1 failed!\n");
        error =  ENXIO;
        goto fail2;
    }
    sc->bar0_bt = rman_get_bustag(sc->bar0res);
    sc->bar0_bh = rman_get_bushandle(sc->bar0res);
    sc->bar1_bt = rman_get_bustag(sc->bar1res);
    sc->bar1_bh = rman_get_bushandle(sc->bar1res);

</programlisting>

      <para>Handles for each base address register are kept in the
        <structname>softc</structname> structure so that they can be
        used to write to the device later.</para>

      <para>These handles can then be used to read or write from the
        device registers with the <function>bus_space_*</function>
        functions.  For example, a driver might contain a shorthand
        function to read from a board specific register like this:</para>

<programlisting>uint16_t
board_read(struct ni_softc *sc, uint16_t address) {
    return bus_space_read_2(sc->bar1_bt, sc->bar1_bh, address);
}
</programlisting>

      <para>Similarly, one could write to the registers with:</para>

<programlisting>void
board_write(struct ni_softc *sc, uint16_t address, uint16_t value) {
    bus_space_write_2(sc->bar1_bt, sc->bar1_bh, address, value);
}
</programlisting>

      <para>These functions exist in 8bit, 16bit, and 32bit versions
        and you should use
        <function>bus_space_{read|write}_{1|2|4}</function>
        accordingly.</para>

    </sect2>
    <sect2>
      <title>Interrupts</title>

      <para>Interrupts are allocated from the object-oriented bus code
        in a way similar to the memory resources.  First an IRQ
        resource must be allocated from the parent bus, and then the
        interrupt handler must be setup to deal with this IRQ.</para>

      <para>Again, a sample from a device
        <function>attach()</function> function says more than
        words.</para>

<programlisting>/* Get the IRQ resource */

    sc->irqid = 0x0;
    sc->irqres = bus_alloc_resource(dev, SYS_RES_IRQ, &amp;(sc->irqid),
				  0, ~0, 1, RF_SHAREABLE | RF_ACTIVE);
    if (sc->irqres == NULL) {
	uprintf("IRQ allocation failed!\n");
	error = ENXIO;
	goto fail3;
    }

    /* Now we should setup the interrupt handler */

    error = bus_setup_intr(dev, sc->irqres, INTR_TYPE_MISC,
			   my_handler, sc, &amp;(sc->handler));
    if (error) {
	printf("Couldn't set up irq\n");
	goto fail4;
    }

    sc->irq_bt = rman_get_bustag(sc->irqres);
    sc->irq_bh = rman_get_bushandle(sc->irqres);
</programlisting>

    </sect2>

    <sect2>
      <title>DMA</title>
      <para>On the PC, peripherals that want to do bus-mastering DMA
      must deal with physical addresses.  This is a problem since
      FreeBSD uses virtual memory and deals almost exclusively with
      virtual addresses.  Fortunately, there is a function,
      <function>vtophys()</function> to help.</para>

<programlisting>#include &lt;vm/vm.h&gt;
#include &lt;vm/pmap.h&gt;

#define vtophys(virtual_address) (...)
</programlisting>

      <para>The solution is a bit different on the alpha however, and
        what we really want is a function called
        <function>vtobus()</function>.</para>

<programlisting>#if defined(__alpha__)
#define vtobus(va)      alpha_XXX_dmamap((vm_offset_t)va)
#else
#define vtobus(va)      vtophys(va)
#endif
</programlisting>

    </sect2>

    <sect2>
      <title>Deallocating Resources</title>

      <para>It is very important to deallocate all of the resources
        that were allocated during <function>attach()</function>.
        Care must be taken to deallocate the correct stuff even on a
        failure condition so that the system will remain usable while
        your driver dies.</para>

    </sect2>
  </sect1>

</chapter>