From: marc.zyngier@arm•com (Marc Zyngier)
To: linux-arm-kernel@lists•infradead.org
Subject: Reading twd_base at run-time
Date: Fri, 27 Mar 2015 16:35:50 +0000 [thread overview]
Message-ID: <551586E6.3020200@arm.com> (raw)
In-Reply-To: <55158261.9010108@free.fr>
Hi Mason,
On 27/03/15 16:16, Mason wrote:
> Hello everyone,
>
> In arch/arm/kernel/smp_twd.c, twd_local_timer_register() receives a
> struct twd_local_timer argument, which specifies
>
> 1) the physical address of twd_base
> 2) the twd interrupt number
>
> There's a helper to fill out the static struct: DEFINE_TWD_LOCAL_TIMER()
>
> But it seems to me (please correct me if I'm wrong) that the address
> of twd_base can be read at run-time, making it one less parameter to
> specify by hand at compile-time (with the risk that a HW engineer
> change the address in the next chip with no warning).
The main problem with that is that said HW engineer has ^%$%^%-up
PERIPHBASE, and that you can't trust it. I've seen a number of these
kicking around.
> Here's an incomplete patch to express my intent:
>
> diff --git a/arch/arm/kernel/smp_twd.c b/arch/arm/kernel/smp_twd.c
> index 6591e26..5177db8 100644
> --- a/arch/arm/kernel/smp_twd.c
> +++ b/arch/arm/kernel/smp_twd.c
> @@ -369,14 +369,14 @@ out_free:
> return err;
> }
>
> -int __init twd_local_timer_register(struct twd_local_timer *tlt)
> +int __init twd_local_timer_register(void)
> {
> if (twd_base || twd_evt)
> return -EBUSY;
>
> - twd_ppi = tlt->res[1].start;
> + twd_ppi = 29;
>
> - twd_base = ioremap(tlt->res[0].start, resource_size(&tlt->res[0]));
> + twd_base = ioremap(scu_a9_get_base() + 0x600, 0x10);
> if (!twd_base)
> return -ENOMEM;
>
>
> As far as I can tell, all platforms use 29 for twd_ppi, but I can make
> sure if people agree this patch is indeed an improvement.
I don't think we'll see that many new platforms not using DT, so this
would effectively remove one line from the helper, and generate a bit of
churn on platforms that are usually left in a dusty corner...
M.
--
Jazz is not dead. It just smells funny...
next prev parent reply other threads:[~2015-03-27 16:35 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-03-27 16:16 Reading twd_base at run-time Mason
2015-03-27 16:35 ` Marc Zyngier [this message]
2015-03-27 20:33 ` Mason
2015-03-27 20:53 ` Russell King - ARM Linux
2015-04-01 12:07 ` Mason
2015-04-01 12:12 ` Russell King - ARM Linux
2015-04-01 12:47 ` Mason
2015-04-01 12:28 ` Marc Zyngier
2015-04-01 12:47 ` Mason
2015-04-01 13:01 ` Mason
2015-04-01 13:14 ` Marc Zyngier
2015-04-01 14:39 ` Mason
2015-04-01 14:56 ` Marc Zyngier
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