linux-kernel - Re: [PATCH] HVC: do not request the irq twice.

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Date:	Thu, 22 Jan 2009 20:09:43 +0100
From:	Christian Borntraeger <borntraeger@...ibm.com>
To:	Ian Campbell <Ian.Campbell@...rix.com>
Cc:	linux-kernel@...r.kernel.org, Milton Miller <miltonm@....com>,
	Hendrik Brueckner <brueckner@...ux.vnet.ibm.com>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	Rusty Russell <rusty@...tcorp.com.au>
Subject: Re: [PATCH] HVC: do not request the irq twice.

Am Thursday 22 January 2009 18:56:08 schrieb Ian Campbell:
> --- a/drivers/char/hvc_irq.c
> +++ b/drivers/char/hvc_irq.c
> @@ -28,6 +28,10 @@ int notifier_add_irq(struct hvc_struct *hp, int irq)
>  		hp->irq_requested = 0;
>  		return 0;
>  	}
> +
> +	if (hp->irq_requested)
> +		return 0;
> +
>  	rc = request_irq(irq, hvc_handle_interrupt, IRQF_DISABLED,
>  			   "hvc_console", hp);
>  	if (!rc)

Unfortunately I have no system with an irq based hvc console - I cannot test 
this patch. Anyway, the patch looks sane:

Reviewed-by: Christian Borntraeger <borntraeger@...ibm.com>

If this really fixes a problem, I am asking myself, if notifier_del can be 
called several times as well. If yes, it might be better to call free_irq at 
the last notifier_del - which means we need proper refcounting. Otherwise the 
console switches into polling mode....

Christian, blaming Rusty for using hvc_console in virtio_console which made me 
somehow responsible for this code...  ;-)
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