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drm: Improve manual IRQ installation documentation
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Define the rules for using irqs from drm drivers.

Signed-off-by: Laurent Pinchart <laurent.pinchart+renesas@ideasonboard.com>
Reviewed-by: Daniel Vetter <daniel.vetter@ffwll.ch>
Signed-off-by: Dave Airlie <airlied@redhat.com>
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Laurent Pinchart authored and Dave Airlie committed Jun 28, 2013
1 parent da34242 commit 02b6298
Showing 1 changed file with 70 additions and 48 deletions.
118 changes: 70 additions & 48 deletions Documentation/DocBook/drm.tmpl
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<varlistentry>
<term>DRIVER_HAVE_IRQ</term><term>DRIVER_IRQ_SHARED</term>
<listitem><para>
DRIVER_HAVE_IRQ indicates whether the driver has an IRQ handler. The
DRM core will automatically register an interrupt handler when the
flag is set. DRIVER_IRQ_SHARED indicates whether the device &amp;
handler support shared IRQs (note that this is required of PCI
drivers).
DRIVER_HAVE_IRQ indicates whether the driver has an IRQ handler
managed by the DRM Core. The core will support simple IRQ handler
installation when the flag is set. The installation process is
described in <xref linkend="drm-irq-registration"/>.</para>
<para>DRIVER_IRQ_SHARED indicates whether the device &amp; handler
support shared IRQs (note that this is required of PCI drivers).
</para></listitem>
</varlistentry>
<varlistentry>
Expand Down Expand Up @@ -344,50 +345,71 @@ char *date;</synopsis>
The DRM core tries to facilitate IRQ handler registration and
unregistration by providing <function>drm_irq_install</function> and
<function>drm_irq_uninstall</function> functions. Those functions only
support a single interrupt per device.
</para>
<!--!Fdrivers/char/drm/drm_irq.c drm_irq_install-->
<para>
Both functions get the device IRQ by calling
<function>drm_dev_to_irq</function>. This inline function will call a
bus-specific operation to retrieve the IRQ number. For platform devices,
<function>platform_get_irq</function>(..., 0) is used to retrieve the
IRQ number.
</para>
<para>
<function>drm_irq_install</function> starts by calling the
<methodname>irq_preinstall</methodname> driver operation. The operation
is optional and must make sure that the interrupt will not get fired by
clearing all pending interrupt flags or disabling the interrupt.
</para>
<para>
The IRQ will then be requested by a call to
<function>request_irq</function>. If the DRIVER_IRQ_SHARED driver
feature flag is set, a shared (IRQF_SHARED) IRQ handler will be
requested.
</para>
<para>
The IRQ handler function must be provided as the mandatory irq_handler
driver operation. It will get passed directly to
<function>request_irq</function> and thus has the same prototype as all
IRQ handlers. It will get called with a pointer to the DRM device as the
second argument.
</para>
<para>
Finally the function calls the optional
<methodname>irq_postinstall</methodname> driver operation. The operation
usually enables interrupts (excluding the vblank interrupt, which is
enabled separately), but drivers may choose to enable/disable interrupts
at a different time.
</para>
<para>
<function>drm_irq_uninstall</function> is similarly used to uninstall an
IRQ handler. It starts by waking up all processes waiting on a vblank
interrupt to make sure they don't hang, and then calls the optional
<methodname>irq_uninstall</methodname> driver operation. The operation
must disable all hardware interrupts. Finally the function frees the IRQ
by calling <function>free_irq</function>.
support a single interrupt per device, devices that use more than one
IRQs need to be handled manually.
</para>
<sect4>
<title>Managed IRQ Registration</title>
<para>
Both the <function>drm_irq_install</function> and
<function>drm_irq_uninstall</function> functions get the device IRQ by
calling <function>drm_dev_to_irq</function>. This inline function will
call a bus-specific operation to retrieve the IRQ number. For platform
devices, <function>platform_get_irq</function>(..., 0) is used to
retrieve the IRQ number.
</para>
<para>
<function>drm_irq_install</function> starts by calling the
<methodname>irq_preinstall</methodname> driver operation. The operation
is optional and must make sure that the interrupt will not get fired by
clearing all pending interrupt flags or disabling the interrupt.
</para>
<para>
The IRQ will then be requested by a call to
<function>request_irq</function>. If the DRIVER_IRQ_SHARED driver
feature flag is set, a shared (IRQF_SHARED) IRQ handler will be
requested.
</para>
<para>
The IRQ handler function must be provided as the mandatory irq_handler
driver operation. It will get passed directly to
<function>request_irq</function> and thus has the same prototype as all
IRQ handlers. It will get called with a pointer to the DRM device as the
second argument.
</para>
<para>
Finally the function calls the optional
<methodname>irq_postinstall</methodname> driver operation. The operation
usually enables interrupts (excluding the vblank interrupt, which is
enabled separately), but drivers may choose to enable/disable interrupts
at a different time.
</para>
<para>
<function>drm_irq_uninstall</function> is similarly used to uninstall an
IRQ handler. It starts by waking up all processes waiting on a vblank
interrupt to make sure they don't hang, and then calls the optional
<methodname>irq_uninstall</methodname> driver operation. The operation
must disable all hardware interrupts. Finally the function frees the IRQ
by calling <function>free_irq</function>.
</para>
</sect4>
<sect4>
<title>Manual IRQ Registration</title>
<para>
Drivers that require multiple interrupt handlers can't use the managed
IRQ registration functions. In that case IRQs must be registered and
unregistered manually (usually with the <function>request_irq</function>
and <function>free_irq</function> functions, or their devm_* equivalent).
</para>
<para>
When manually registering IRQs, drivers must not set the DRIVER_HAVE_IRQ
driver feature flag, and must not provide the
<methodname>irq_handler</methodname> driver operation. They must set the
<structname>drm_device</structname> <structfield>irq_enabled</structfield>
field to 1 upon registration of the IRQs, and clear it to 0 after
unregistering the IRQs.
</para>
</sect4>
</sect3>
<sect3>
<title>Memory Manager Initialization</title>
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