From mboxrd@z Thu Jan 1 00:00:00 1970 From: khilman@deeprootsystems.com (Kevin Hilman) Date: Tue, 23 Oct 2012 07:14:48 -0700 Subject: [PATCH v2] arm: sched: stop sched_clock() during suspend In-Reply-To: <1350971854-9161-1-git-send-email-balbi@ti.com> (Felipe Balbi's message of "Tue, 23 Oct 2012 08:57:34 +0300") References: <873916h1yi.fsf@deeprootsystems.com> <1350971854-9161-1-git-send-email-balbi@ti.com> Message-ID: <87mwzdcm1z.fsf@deeprootsystems.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org Felipe Balbi writes: > The scheduler imposes a requirement to sched_clock() > which is to stop the clock during suspend, if we don't > do that any RT thread will be rescheduled in the future > which might cause any sort of problems. > > This became an issue on OMAP when we converted omap-i2c.c > to use threaded IRQs, it turned out that depending on how > much time we spent on suspend, the I2C IRQ thread would > end up being rescheduled so far in the future that I2C > transfers would timeout and, because omap_hsmmc depends > on an I2C-connected device to detect if an MMC card is > inserted in the slot, our rootfs would just vanish. > > arch/arm/kernel/sched_clock.c already had an optional > implementation (sched_clock_needs_suspend()) which would > handle scheduler's requirement properly, what this patch > does is simply to make that implementation non-optional. > > Note that this has the side-effect that printk timings > won't reflect the actual time spent on suspend so other > methods to measure that will have to be used. > > This has been tested with beagleboard XM (OMAP3630) and > pandaboard rev A3 (OMAP4430). Suspend to RAM is now working > after this patch. > > Signed-off-by: Felipe Balbi Acked-by: Kevin Hilman