Add a common struct clk
in [Kernel]
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From: Uwe Kleine-König on 14 Jun 2010 02:50 Hello Lothar, On Mon, Jun 14, 2010 at 08:39:21AM +0200, Lothar Wa�mann wrote: > Hi, > > Benjamin Herrenschmidt writes: > > On Fri, 2010-06-11 at 12:08 +0200, Lothar Wa�mann wrote: > > > Hi, > > > > > > > > > > Using a mutex in clk_enable()/clk_disable() is a bad idea, since that > > > > > > > makes it impossible to call those functions in interrupt context. > > > > IMHO if a device generates an irq its clock should already be on. This > > > > way you don't need to enable or disable a clock in irq context. > > > > > > > You may want to disable a clock in the IRQ handler. The VPU driver in > > > the Freescale BSP for i.MX51 does exactly this. > > > Anyway I don't see any reason for using a mutex here instead of > > > spin_lock_irq_save() as all other implementations do. > > > > Because you suddenly make it impossible to sleep inside enable/disable > ^^^^^^^^^^^^^^^^^^^^^^^^^^^ > ??? > All implementations so far use spin_lock_irq_save()! > > How would you be able to sleep with a mutex held? > If you hold a lock you must not sleep, no matter what sort of lock it > is. That's wrong. With a mutex hold you may sleep. Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-K�nig | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Lothar Waßmann on 14 Jun 2010 03:00 Hi, Uwe Kleine-K�nig writes: > Hello Lothar, > > On Mon, Jun 14, 2010 at 08:39:21AM +0200, Lothar Wa�mann wrote: > > Hi, > > > > Benjamin Herrenschmidt writes: > > > On Fri, 2010-06-11 at 12:08 +0200, Lothar Wa�mann wrote: > > > > Hi, > > > > > > > > > > > > Using a mutex in clk_enable()/clk_disable() is a bad idea, since that > > > > > > > > makes it impossible to call those functions in interrupt context. > > > > > IMHO if a device generates an irq its clock should already be on. This > > > > > way you don't need to enable or disable a clock in irq context. > > > > > > > > > You may want to disable a clock in the IRQ handler. The VPU driver in > > > > the Freescale BSP for i.MX51 does exactly this. > > > > Anyway I don't see any reason for using a mutex here instead of > > > > spin_lock_irq_save() as all other implementations do. > > > > > > Because you suddenly make it impossible to sleep inside enable/disable > > ^^^^^^^^^^^^^^^^^^^^^^^^^^^ > > ??? > > All implementations so far use spin_lock_irq_save()! > > > > How would you be able to sleep with a mutex held? > > If you hold a lock you must not sleep, no matter what sort of lock it > > is. > That's wrong. With a mutex hold you may sleep. > OK, you're right. But still all other implementations (omap, mxc, davinci,...) use spin_lock_irqsave() to protect the enable/disable functions and don't seem to have any problem with this. Is there any reason to change this, or make it inconsistent for one arch? And arch/arm/plat-s3c/clock.c has the following comment: |/* We originally used an mutex here, but some contexts (see resume) | * are calling functions such as clk_set_parent() with IRQs disabled | * causing an BUG to be triggered. | */ |DEFINE_SPINLOCK(clocks_lock); Lothar Wa�mann -- ___________________________________________________________ Ka-Ro electronics GmbH | Pascalstra�e 22 | D - 52076 Aachen Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10 Gesch�ftsf�hrer: Matthias Kaussen Handelsregistereintrag: Amtsgericht Aachen, HRB 4996 www.karo-electronics.de | info(a)karo-electronics.de ___________________________________________________________ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Benjamin Herrenschmidt on 14 Jun 2010 05:30 On Mon, 2010-06-14 at 08:39 +0200, Lothar Waßmann wrote: > All implementations so far use spin_lock_irq_save()! Nothing prevents your implementation to be a tad smarter. > How would you be able to sleep with a mutex held? > If you hold a lock you must not sleep, no matter what sort of lock it > is. You can perfectly sleep with a mutex held. You -do- have to be careful of course to ensure you aren't going to do silly thing like re-enter and try to take it twice, or A->B B->A deadlocks, but in the typical case of wanting to use a msleep rather than udelay, it works very well :-) Cheers, Ben. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Lothar Waßmann on 14 Jun 2010 05:40 Benjamin Herrenschmidt writes: > On Mon, 2010-06-14 at 08:39 +0200, Lothar Wa�mann wrote: > > All implementations so far use spin_lock_irq_save()! > > Nothing prevents your implementation to be a tad smarter. > I vote for consistency, so that device drivers can be kept arch independent instead of having to care about implentation details of each arch. Lothar Wa�mann -- ___________________________________________________________ Ka-Ro electronics GmbH | Pascalstra�e 22 | D - 52076 Aachen Phone: +49 2408 1402-0 | Fax: +49 2408 1402-10 Gesch�ftsf�hrer: Matthias Kaussen Handelsregistereintrag: Amtsgericht Aachen, HRB 4996 www.karo-electronics.de | info(a)karo-electronics.de ___________________________________________________________ -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
From: Uwe Kleine-König on 14 Jun 2010 05:40
Hello, > And arch/arm/plat-s3c/clock.c has the following comment: > |/* We originally used an mutex here, but some contexts (see resume) > | * are calling functions such as clk_set_parent() with IRQs disabled > | * causing an BUG to be triggered. > | */ > |DEFINE_SPINLOCK(clocks_lock); I wonder why it's needed to reparent clocks during resume. And where exactly IRQs are disabled. Hmm, this comment was initially introduced by v2.6.28-rc7-180-gc3391e3, its commit log talks about cpufreq, not resume. Ben (Dooks): Is this still relevant? Best regards Uwe -- Pengutronix e.K. | Uwe Kleine-K�nig | Industrial Linux Solutions | http://www.pengutronix.de/ | -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |