linux-kernel - Re: [RFC] [PATCH 02/62] mpu401:snd_mpu401_uart_new(): split semantic of irq

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Date:	Thu, 8 Sep 2011 22:45:20 +0800
From:	Yong Zhang <yong.zhang0@...il.com>
To:	Clemens Ladisch <clemens@...isch.de>
Cc:	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...e.hu,
	Jaroslav Kysela <perex@...ex.cz>, Takashi Iwai <tiwai@...e.de>,
	Uwe Kleine-König 
	<u.kleine-koenig@...gutronix.de>, Jiri Kosina <jkosina@...e.cz>,
	Andreas Mohr <andi@...as.de>,
	Lucas De Marchi <lucas.demarchi@...fusion.mobi>,
	Julia Lawall <julia@...u.dk>,
	Ondrej Zary <linux@...nbow-software.org>,
	Dan Carpenter <error27@...il.com>,
	Joe Perches <joe@...ches.com>, alsa-devel@...a-project.org
Subject: Re: [RFC] [PATCH 02/62] mpu401:snd_mpu401_uart_new(): split
 semantic of irq_flags

On Thu, Sep 08, 2011 at 03:58:45PM +0200, Clemens Ladisch wrote:
> 
> The MPU-401 in UART mode is a very simple and stupid MIDI interface,
> which is used on very many sound cards.  Depending on the actual
> hardware implementation, it gets its own interrupt which may be
> exclusive or sharable, or it is integrated into the interrupt handling
> of the main sound card which means that the sound driver has to call the
> mpu401 interrupt handler explicitly.
> 
> Here, "no interrupt" and "already reserved" actually mean the same thing,
> i.e., that the interrupt handling is the responsibility of some other
> driver.

Thanks. If my understanding is correct, in below combination:

	irq		irq_flags
1)      >=0             >0          /* valid */
2)      >=0             =0          /* invalid, irq should be '-1' */
3)      -1              >0          /* valid, irq_flags just mean real irq_falgs,
                                       but actually there is no irq */
4)      -1              =0          /* valid */

my comment will be true, and we could simplify snd_mpu401_uart_new()
like below:

-	if (irq >= 0 && irq_flags) {
+	if (irq >= 0) {

right?


And then we should audit all the callers of snd_mpu401_uart_new()
to check if they provide the cerrect irq number, but IMOH, that
would more difficult than keeping 'want_irq/irq_reserved'.

Thanks,
Yong
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