linux-kernel - Re: [PATCH] geode-mfgpt: restore previous behavior for selecting IRQ

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Message-ID: <20100118103430.6480d1a8@mycelium.queued.net>
Date:	Mon, 18 Jan 2010 10:34:30 -0500
From:	Andres Salomon <dilinger@...labora.co.uk>
To:	Jens Rottmann <JRottmann@...PERTEmbedded.de>
Cc:	linux-kernel@...r.kernel.org, linux-geode@...badil.infradead.org
Subject: Re: [PATCH] geode-mfgpt: restore previous behavior for selecting
 IRQ

On Tue, 12 Jan 2010 11:14:30 +0100
Jens Rottmann <JRottmann@...PERTEmbedded.de> wrote:

> geode-mfgpt: restore previous behavior for selecting IRQ
> 
> The MFGPT IRQ used to be, in order of decreasing priority,
> * IRQ supplied by the user as a boot-time parameter,
> * IRQ previously set by the BIOS or another driver,
> * default IRQ given at compile time.
> 
> Return to this behavior, which got broken when splitting the
> MFGPT/clocksource driver for 2.6.33-rc1.
> 
> Signed-off-by: Jens Rottmann <JRottmann@...PERTEmbedded.de>
> ---
> 
> Hi Andres,
> 
> a bit more detail. Up to 2.6.32 the MFGPT IRQ was chosen like this:
> 
> static int irq;
> static int __init mfgpt_setup(char *str)
> {
> 	get_option(&str, &irq);
> 	return 1;
> }
> __setup("mfgpt_irq=", mfgpt_setup);
> [...]
> /* Choose IRQ: if none supplied, keep IRQ already set or use default
> */ if (!*irq)
> 	*irq = (zsel >> shift) & 0xF;	// may have been set by
> the BIOS if (!*irq)
> 	*irq = MFGPT_DEFAULT_IRQ;	// #defined as 7
> 
> The code in 2.6.33-rc3 after the MFGPT/clocksource split looks like
> this:
> 
> static int timer_irq = CONFIG_CS5535_MFGPT_DEFAULT_IRQ;	//
> defaults to 7 module_param_named(irq, timer_irq, int, 0644);
> [...]
> if (!*irq)
> 	*irq = (zsel >> shift) & 0xF;		// gets ignored
> now if (!*irq)
> 	*irq = CONFIG_CS5535_MFGPT_DEFAULT_IRQ;	// again!?
> 
> The patch removes the first of the two ocurrances of
> CONFIG_CS5535_MFGPT_DEFAULT_IRQ, reverting the IRQ selection to the
> previous (working) behavior.

You're right, thanks.  For the patch below:

Acked-by: Andres Salomon <dilinger@...labora.co.uk>


> 
> 
> BTW, while looking into this I stumbled upon the fact that
> cs5535_mfgpt_init() doesn't free up the timer in the error path if
> cs5535_mfgpt_setup_irq() or setup_irq() fail. However, some comments
> in cs5535-mfgpt.c (stating that it's not possible to release the
> individual timer hardware) make me think this might have been skipped
> on purpose? Could you please have a look?

Oh, you mean in the clockevt driver?  Yeah, we can't really free the
timer, unfortunately.

It actually might not be a bad idea to reverse the code so that the IRQ
allocation happens first, since we can clean that up if mfgpt
allocation fails.   Feel like sending a patch? :)



> 
> Thanks,
> Jens
> 
> --- linux-2.6.33-rc3-git4/drivers/clocksource/cs5535-clockevt.c
> +++ previous_behavior/drivers/clocksource/cs5535-clockevt.c
> @@ -21,7 +21,7 @@
>  
>  #define DRV_NAME "cs5535-clockevt"
>  
> -static int timer_irq = CONFIG_CS5535_MFGPT_DEFAULT_IRQ;
> +static int timer_irq;
>  module_param_named(irq, timer_irq, int, 0644);
>  MODULE_PARM_DESC(irq, "Which IRQ to use for the clock source MFGPT
> ticks."); 
> _
> 
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