linux-kernel - Re: [PATCH 3/3] Allow setup

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Message-ID: <20101201112410.GL2916@linux-mips.org>
Date:	Wed, 1 Dec 2010 11:24:10 +0000
From:	Ralf Baechle <ralf@...ux-mips.org>
To:	Anoop P <anoop.pa@...il.com>
Cc:	linux-mips@...ux-mips.org, dvomlehn@...co.com,
	David Howells <dhowells@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	David Daney <ddaney@...iumnetworks.com>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 3/3] Allow setup_irq call for VPE1 timer.

On Thu, Nov 25, 2010 at 08:37:12PM +0530, Anoop P wrote:

> From: Anoop P A <anoop.pa@...il.com>
> 
> VSMP configuration can have seperate timer interrupts for each VPE.Need to setup IRQ for VPE1 timer.

> +#ifndef CONFIG_MIPS_MT_SMP
>  	if (cp0_timer_irq_installed)
>  		return 0;
> -
> +#endif
>  	cp0_timer_irq_installed = 1;
>  
>  	setup_irq(irq, &c0_compare_irqaction);

On the stylistic side adding an #ifdef gives me wrinkles.

With CONFIG_MIPS_MT_SMP this patch results in sharing c0_compare_irqaction
between multiple interrupts which is broken.  Struct irqaction contains
the interrupt number, all registered irqaction structs are part of a chained
list via its ->next member and also there is a per interrupt proc directory.

To fix this properly you'll have to introduce do a bit of bookkeeping - you
want to register each interrupt only once - and allocate a struct irqaction
per registered timer interrupt.

The allocation is made a little trickier by kmalloc not being available
yet by the time this code is getting invoked via time_init() so you'll
have to move it to run via the late_time_init hook like x86:

static __init void x86_late_time_init(void)
{
	... do the real work ...
}

/* ... */

void __init time_init(void)
{
        late_time_init = x86_late_time_init;
}

Which makes me wonder if there is a reason why we need to have both
time_init() and late_time_init() - can't we just move the time_init()?

  Ralf
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