linux-kernel - Re: [UPDATED] [PATCH 61/62] Documentation: irq: Change documents related to IRQF

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Date:	Fri, 9 Sep 2011 10:25:18 +0200
From:	"Rolf Eike Beer" <eike-kernel@...tec.de>
To:	"Yong Zhang" <yong.zhang0@...il.com>
Cc:	"Randy Dunlap" <rdunlap@...otime.net>,
	linux-kernel@...r.kernel.org, tglx@...utronix.de, mingo@...e.hu,
	"Jesse Barnes" <jbarnes@...tuousgeek.org>,
	linux-pci@...r.kernel.org, linux-doc@...r.kernel.org
Subject: Re: [UPDATED] [PATCH 61/62] Documentation: irq: Change documents
 related to IRQF_DISABLED

> IRQF_DISABLED is a NOOP now, place where suggest to use this
> flag also doesn't make sense any more.
>
> Signed-off-by: Yong Zhang <yong.zhang0@...il.com>
> ---
>  Documentation/PCI/MSI-HOWTO.txt  |   21 ---------------------
>  Documentation/scsi/ncr53c8xx.txt |    4 +++-
>  Documentation/scsi/tmscsim.txt   |    4 ++--
>  3 files changed, 5 insertions(+), 24 deletions(-)
>
> diff --git a/Documentation/PCI/MSI-HOWTO.txt
> b/Documentation/PCI/MSI-HOWTO.txt
> index 53e6fca..b3f514d 100644
> --- a/Documentation/PCI/MSI-HOWTO.txt
> +++ b/Documentation/PCI/MSI-HOWTO.txt
> @@ -255,27 +255,6 @@ as many vectors for MSI as it could for MSI-X.  On
> some platforms, MSI
>  interrupts must all be targeted at the same set of CPUs whereas MSI-X
>  interrupts can all be targeted at different CPUs.
>
> -4.5.2 Spinlocks
> -
> -Most device drivers have a per-device spinlock which is taken in the
> -interrupt handler.  With pin-based interrupts or a single MSI, it is not
> -necessary to disable interrupts (Linux guarantees the same interrupt will
> -not be re-entered).  If a device uses multiple interrupts, the driver
> -must disable interrupts while the lock is held.  If the device sends
> -a different interrupt, the driver will deadlock trying to recursively
> -acquire the spinlock.
> -
> -There are two solutions.  The first is to take the lock with
> -spin_lock_irqsave() or spin_lock_irq() (see
> -Documentation/DocBook/kernel-locking).  The second is to specify
> -IRQF_DISABLED to request_irq() so that the kernel runs the entire
> -interrupt routine with interrupts disabled.
> -
> -If your MSI interrupt routine does not hold the lock for the whole time
> -it is running, the first solution may be best.  The second solution is
> -normally preferred as it avoids making two transitions from interrupt
> -disabled to enabled and back again.

Is this whole section really obsolete now? Or is it only the part that
suggests IRQF_DISABLED?

Eike
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