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-rw-r--r--Documentation/DocBook/uio-howto.tmpl88
1 files changed, 88 insertions, 0 deletions
diff --git a/Documentation/DocBook/uio-howto.tmpl b/Documentation/DocBook/uio-howto.tmpl
index b787e4721c90..52e1b79ce0e6 100644
--- a/Documentation/DocBook/uio-howto.tmpl
+++ b/Documentation/DocBook/uio-howto.tmpl
@@ -42,6 +42,12 @@ GPL version 2.
42 42
43<revhistory> 43<revhistory>
44 <revision> 44 <revision>
45 <revnumber>0.7</revnumber>
46 <date>2008-12-23</date>
47 <authorinitials>hjk</authorinitials>
48 <revremark>Added generic platform drivers and offset attribute.</revremark>
49 </revision>
50 <revision>
45 <revnumber>0.6</revnumber> 51 <revnumber>0.6</revnumber>
46 <date>2008-12-05</date> 52 <date>2008-12-05</date>
47 <authorinitials>hjk</authorinitials> 53 <authorinitials>hjk</authorinitials>
@@ -312,6 +318,16 @@ interested in translating it, please email me
312 pointed to by addr. 318 pointed to by addr.
313 </para> 319 </para>
314</listitem> 320</listitem>
321<listitem>
322 <para>
323 <filename>offset</filename>: The offset, in bytes, that has to be
324 added to the pointer returned by <function>mmap()</function> to get
325 to the actual device memory. This is important if the device's memory
326 is not page aligned. Remember that pointers returned by
327 <function>mmap()</function> are always page aligned, so it is good
328 style to always add this offset.
329 </para>
330</listitem>
315</itemizedlist> 331</itemizedlist>
316 332
317<para> 333<para>
@@ -594,6 +610,78 @@ framework to set up sysfs files for this region. Simply leave it alone.
594 </para> 610 </para>
595</sect1> 611</sect1>
596 612
613<sect1 id="using_uio_pdrv">
614<title>Using uio_pdrv for platform devices</title>
615 <para>
616 In many cases, UIO drivers for platform devices can be handled in a
617 generic way. In the same place where you define your
618 <varname>struct platform_device</varname>, you simply also implement
619 your interrupt handler and fill your
620 <varname>struct uio_info</varname>. A pointer to this
621 <varname>struct uio_info</varname> is then used as
622 <varname>platform_data</varname> for your platform device.
623 </para>
624 <para>
625 You also need to set up an array of <varname>struct resource</varname>
626 containing addresses and sizes of your memory mappings. This
627 information is passed to the driver using the
628 <varname>.resource</varname> and <varname>.num_resources</varname>
629 elements of <varname>struct platform_device</varname>.
630 </para>
631 <para>
632 You now have to set the <varname>.name</varname> element of
633 <varname>struct platform_device</varname> to
634 <varname>"uio_pdrv"</varname> to use the generic UIO platform device
635 driver. This driver will fill the <varname>mem[]</varname> array
636 according to the resources given, and register the device.
637 </para>
638 <para>
639 The advantage of this approach is that you only have to edit a file
640 you need to edit anyway. You do not have to create an extra driver.
641 </para>
642</sect1>
643
644<sect1 id="using_uio_pdrv_genirq">
645<title>Using uio_pdrv_genirq for platform devices</title>
646 <para>
647 Especially in embedded devices, you frequently find chips where the
648 irq pin is tied to its own dedicated interrupt line. In such cases,
649 where you can be really sure the interrupt is not shared, we can take
650 the concept of <varname>uio_pdrv</varname> one step further and use a
651 generic interrupt handler. That's what
652 <varname>uio_pdrv_genirq</varname> does.
653 </para>
654 <para>
655 The setup for this driver is the same as described above for
656 <varname>uio_pdrv</varname>, except that you do not implement an
657 interrupt handler. The <varname>.handler</varname> element of
658 <varname>struct uio_info</varname> must remain
659 <varname>NULL</varname>. The <varname>.irq_flags</varname> element
660 must not contain <varname>IRQF_SHARED</varname>.
661 </para>
662 <para>
663 You will set the <varname>.name</varname> element of
664 <varname>struct platform_device</varname> to
665 <varname>"uio_pdrv_genirq"</varname> to use this driver.
666 </para>
667 <para>
668 The generic interrupt handler of <varname>uio_pdrv_genirq</varname>
669 will simply disable the interrupt line using
670 <function>disable_irq_nosync()</function>. After doing its work,
671 userspace can reenable the interrupt by writing 0x00000001 to the UIO
672 device file. The driver already implements an
673 <function>irq_control()</function> to make this possible, you must not
674 implement your own.
675 </para>
676 <para>
677 Using <varname>uio_pdrv_genirq</varname> not only saves a few lines of
678 interrupt handler code. You also do not need to know anything about
679 the chip's internal registers to create the kernel part of the driver.
680 All you need to know is the irq number of the pin the chip is
681 connected to.
682 </para>
683</sect1>
684
597</chapter> 685</chapter>
598 686
599<chapter id="userspace_driver" xreflabel="Writing a driver in user space"> 687<chapter id="userspace_driver" xreflabel="Writing a driver in user space">