linux-kernel - [PATCH] cs5535-clockevt: don't ignore MFGPT on SMP-capable kernels

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Message-ID: <4EF1FE5C.6040101@LiPPERTEmbedded.de>
Date:	Wed, 21 Dec 2011 16:42:20 +0100
From:	Jens Rottmann <JRottmann@...PERTEmbedded.de>
To:	Andres Salomon <dilinger@...ued.net>
CC:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	linux-geode@...ts.infradead.org
Subject: [PATCH] cs5535-clockevt: don't ignore MFGPT on SMP-capable kernels

cs5535-clockevt: don't ignore MFGPT on SMP-capable kernels

On SMP-capable kernels (e.g. generic distro kernel) the cs5535-clockevt driver
loads but is not actually used.

Setting cpumask to cpu_all_mask works for UP-only kernels, but if compiled for
SMP - though still running on the same UP hardware -
kernel/time/tick-common.c:tick_check_new_device() reads this as "non-cpu-local"
and silently ignores the device.

If we leave cpumask unset clockevents_register_device() will initialize it and
the cs5535-clockevt driver will be used no matter how the kernel was compiled.
Should anyone ever manage to stick a CS553x in an SMP system (is this even
possible?) then a warning will be printed.  This is fine as the cs5535-clockevt
driver was never written/tested for SMP.

If bisecting led you here this patch may have exposed a pre-existing MFGPT
problem.  Configure for UP-only and re-check.

Signed-off-by: Jens Rottmann <JRottmann@...PERTEmbedded.de>
---

--- linux-3.2-rc6/drivers/clocksource/cs5535-clockevt.c
+++ use_mfgpt_on_smp_kernels/drivers/clocksource/cs5535-clockevt.c
@@ -100,7 +100,6 @@ static struct clock_event_device cs5535_
 	.set_mode = mfgpt_set_mode,
 	.set_next_event = mfgpt_next_event,
 	.rating = 250,
-	.cpumask = cpu_all_mask,
 	.shift = 32
 };

_

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