drm: Improve manual IRQ installation documentation

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>

Documentation/DocBook/drm.tmpl

@@ -186,11 +186,12 @@
           <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>
@@ -344,15 +345,18 @@ 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.
+          support a single interrupt per device, devices that use more than one
+          IRQs need to be handled manually.
         </para>
-  <!--!Fdrivers/char/drm/drm_irq.c drm_irq_install-->
+        <sect4>
+          <title>Managed IRQ Registration</title>
           <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.
+            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
@@ -388,6 +392,24 @@ char *date;</synopsis>
             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>