linux-kernel - Re: [PATCH try #2] Input/Joystick Driver: add support AD7142 joystick driver

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Message-ID: <d120d5000710121323w563cf328s315f95eb6a857b75@mail.gmail.com>
Date:	Fri, 12 Oct 2007 16:23:15 -0400
From:	"Dmitry Torokhov" <dmitry.torokhov@...il.com>
To:	"Ahmed S. Darwish" <darwish.07@...il.com>
Cc:	"Bryan Wu" <bryan.wu@...log.com>,
	linux-input@...ey.karlin.mff.cuni.cz,
	linux-joystick@...ey.karlin.mff.cuni.cz,
	linux-kernel@...r.kernel.org, akpm@...ux-foundation.org
Subject: Re: [PATCH try #2] Input/Joystick Driver: add support AD7142 joystick driver

On 10/12/07, Ahmed S. Darwish <darwish.07@...il.com> wrote:
> On Fri, Oct 12, 2007 at 01:29:31PM -0400, Dmitry Torokhov wrote:
> >
> > > Isn't disabling device interrupts from the begining of the ISR "ad7142_interrupt"
> > > till the kthread "ad7142_thread" got waked-up and scheduled a long time,
> > > espicially if there's a high load on the userspace side ?
> > >
> >
> > It is OK - you disable a specific interrupt line preventing it from
> > raising any more IRQs until current one is serviced.
>
> Won't this affect system responsiveness if the IRQ line was shared ?

You are right, this would not work in case of shared IRQs. Hovewer
this driver is for an embedded arch and the line is not shared.

>
> >
> > This is different from disabling interrupts on CPU.
> >
>
> mm, Why disabling interrupts in general. Doesn't IRQ hanlers of the same kind got
> executed in a serialized fashion even on SMPs ?. If so, why not just wakeup our
> custom-thread or use workqueues and let them do their business ?

Because you don't want CPU to be continually interrupted while untill
right thread gets scheduled. I think using work[queue] is the best
solution for this driver, but you still want to mask that particular
IRQ off until you do the read.

-- 
Dmitry
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