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From: Alan Cox <alan@lxorguk.ukuu.org.uk>
To: Davide Ciminaghi <ciminaghi@gnudd.com>
Cc: Mark Brown <broonie@opensource.wolfsonmicro.com>,
	sameo@linux.intel.com, rubini@gnudd.com,
	giancarlo.asnaghi@st.com, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 1/8] sta2x11-mfd : add apb-soc regs driver and factor out common code
Date: Thu, 27 Sep 2012 15:13:14 +0100	[thread overview]
Message-ID: <20120927151314.118c86c1@pyramind.ukuu.org.uk> (raw)
In-Reply-To: <20120927134110.GD6799@mail.gnudd.com>

> as far as I know, nested locks are fine provided that you always take them in
> the same order and release them in the opposite order (lock A, lock B,
> unlock B, unlock A). So my conclusion is that nested spinlocks require
> potential regmap users of sta2x11 registers to take the sta2x11-mfd spinlock
> first. The pattern would be (sctl registers for instance):

The release order does not matter. Taking AB and releasing AB or BA is
fine. Taking AB and dropping B and retaking B is fine. Taking AB and
somewhere else taking BA is not. There are performance reasons in some
cases why taking AB releasing A is best with locks, but thats generally
with sleepable locks.

It's a bit more subtle because you often have other interactions. In
particular people often come unstuck on del_timer_sync or waiting for
workqueues and IRQs to finish (even in free_irq) while holding a lock
that the handler needs to take.

Alan

  parent reply	other threads:[~2012-09-27 14:08 UTC|newest]

Thread overview: 24+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-09-12 10:22 [PATCH 0/8 RESEND] sta2x11-mfd patches ciminaghi
2012-09-12 10:22 ` [PATCH 1/8] sta2x11-mfd : add apb-soc regs driver and factor out common code ciminaghi
2012-09-25 19:20   ` Mark Brown
2012-09-26 14:56     ` Davide Ciminaghi
2012-09-26 15:04       ` Mark Brown
2012-09-26 16:31         ` Davide Ciminaghi
2012-09-26 16:49           ` Mark Brown
2012-09-27  8:39             ` Davide Ciminaghi
2012-09-27  8:56             ` Davide Ciminaghi
2012-09-27 13:41             ` Davide Ciminaghi
2012-09-27 13:49               ` Mark Brown
2012-09-28  8:43                 ` Davide Ciminaghi
2012-09-28 10:52                   ` Mark Brown
2012-09-27 14:13               ` Alan Cox [this message]
2012-09-28 15:29                 ` Davide Ciminaghi
2012-09-12 10:22 ` [PATCH 2/8] sta2x11-mfd : add sta2x11_mfd_get_regs_data() function ciminaghi
2012-09-12 10:22 ` [PATCH 3/8] sta2x11-mfd : use defines for platform devices' names ciminaghi
2012-09-12 10:22 ` [PATCH 4/8] sta2x11-mfd : only add sta2x11_mfd if it hasn't already been added ciminaghi
2012-09-12 10:22 ` [PATCH 5/8] sta2x11-mfd : platform probe: don't mind about gpio platform data ciminaghi
2012-09-12 10:22 ` [PATCH 6/8] sta2x11-mfd : use one lock per device instead of one lock per mfd ciminaghi
2012-09-12 10:22 ` [PATCH 7/8] sta2x11-mfd : add defines for some sta2x11 sctl registers ciminaghi
2012-09-12 10:22 ` [PATCH 8/8] sta2x11-mfd : add myself to copyright ciminaghi
2012-09-16 21:25 ` [PATCH 0/8 RESEND] sta2x11-mfd patches Alessandro Rubini
  -- strict thread matches above, loose matches on Subject: below --
2012-09-12 10:11 ciminaghi
2012-09-12 10:11 ` [PATCH 1/8] sta2x11-mfd : add apb-soc regs driver and factor out common code ciminaghi

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