ALSA: mpu401: clean up interrupt specification
The semantics of snd_mpu401_uart_new()'s interrupt parameters are
somewhat counterintuitive: To prevent the function from allocating its
own interrupt, either the irq number must be invalid, or the irq_flags
parameter must be zero. At the same time, the irq parameter being
invalid specifies that the mpu401 code has to work without an interrupt
allocated by the caller. This implies that, if there is an interrupt
and it is allocated by the caller, the irq parameter must be set to
a valid-looking number which then isn't actually used.
With the removal of IRQF_DISABLED, zero becomes a valid irq_flags value,
which forces us to handle the parameters differently.
This patch introduces a new flag MPU401_INFO_IRQ_HOOK for when the
device interrupt is handled by the caller, and makes the allocation of
the interrupt to depend only on the irq parameter. As suggested by
Takashi, the irq_flags parameter was dropped because, when used, it had
the constant value IRQF_DISABLED.
Signed-off-by: Clemens Ladisch <clemens@ladisch.de>
Signed-off-by: Takashi Iwai <tiwai@suse.de>
diff --git a/Documentation/DocBook/writing-an-alsa-driver.tmpl b/Documentation/DocBook/writing-an-alsa-driver.tmpl
index 598c22f..5de23c0 100644
--- a/Documentation/DocBook/writing-an-alsa-driver.tmpl
+++ b/Documentation/DocBook/writing-an-alsa-driver.tmpl
@@ -4288,7 +4288,7 @@
<![CDATA[
struct snd_rawmidi *rmidi;
snd_mpu401_uart_new(card, 0, MPU401_HW_MPU401, port, info_flags,
- irq, irq_flags, &rmidi);
+ irq, &rmidi);
]]>
</programlisting>
</informalexample>
@@ -4343,6 +4343,13 @@
by itself to start processing the output stream in the irq handler.
</para>
+ <para>
+ If the MPU-401 interface shares its interrupt with the other logical
+ devices on the card, set <constant>MPU401_INFO_IRQ_HOOK</constant>
+ (see <link linkend="midi-interface-interrupt-handler"><citetitle>
+ below</citetitle></link>).
+ </para>
+
<para>
Usually, the port address corresponds to the command port and
port + 1 corresponds to the data port. If not, you may change
@@ -4375,14 +4382,12 @@
</para>
<para>
- The 6th argument specifies the irq number for UART. If the irq
- is already allocated, pass 0 to the 7th argument
- (<parameter>irq_flags</parameter>). Otherwise, pass the flags
- for irq allocation
- (<constant>SA_XXX</constant> bits) to it, and the irq will be
- reserved by the mpu401-uart layer. If the card doesn't generate
- UART interrupts, pass -1 as the irq number. Then a timer
- interrupt will be invoked for polling.
+ The 6th argument specifies the ISA irq number that will be
+ allocated. If no interrupt is to be allocated (because your
+ code is already allocating a shared interrupt, or because the
+ device does not use interrupts), pass -1 instead.
+ For a MPU-401 device without an interrupt, a polling timer
+ will be used instead.
</para>
</section>
@@ -4390,12 +4395,13 @@
<title>Interrupt Handler</title>
<para>
When the interrupt is allocated in
- <function>snd_mpu401_uart_new()</function>, the private
- interrupt handler is used, hence you don't have anything else to do
- than creating the mpu401 stuff. Otherwise, you have to call
- <function>snd_mpu401_uart_interrupt()</function> explicitly when
- a UART interrupt is invoked and checked in your own interrupt
- handler.
+ <function>snd_mpu401_uart_new()</function>, an exclusive ISA
+ interrupt handler is automatically used, hence you don't have
+ anything else to do than creating the mpu401 stuff. Otherwise, you
+ have to set <constant>MPU401_INFO_IRQ_HOOK</constant>, and call
+ <function>snd_mpu401_uart_interrupt()</function> explicitly from your
+ own interrupt handler when it has determined that a UART interrupt
+ has occurred.
</para>
<para>