linux-kernel - Re: [PATCH] - race-free suspend. Was: Re: [linux-pm] [PATCH 0/8] Suspend block api (version 8)

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Message-ID: <20100603032746.014f5c07@schatten.dmk.lab>
Date:	Thu, 3 Jun 2010 03:27:46 +0200
From:	Florian Mickler <florian@...kler.org>
To:	Dmitry Torokhov <dmitry.torokhov@...il.com>
Cc:	Neil Brown <neilb@...e.de>,
	Arve Hjønnevåg <arve@...roid.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	"Rafael J. Wysocki" <rjw@...k.pl>,
	Alan Stern <stern@...land.harvard.edu>,
	Felipe Balbi <felipe.balbi@...ia.com>,
	Peter Zijlstra <peterz@...radead.org>,
	"Paul@...p1.linux-foundation.org" <Paul@...p1.linux-foundation.org>,
	LKML <linux-kernel@...r.kernel.org>,
	Linux OMAP Mailing List <linux-omap@...r.kernel.org>,
	Linux PM <linux-pm@...ts.linux-foundation.org>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	James Bottomley <James.Bottomley@...e.de>
Subject: Re: [PATCH] - race-free suspend. Was: Re: [linux-pm] [PATCH 0/8]
 Suspend block api (version 8)

On Wed, 2 Jun 2010 16:32:44 -0700
Dmitry Torokhov <dmitry.torokhov@...il.com> wrote:

> On Wed, Jun 02, 2010 at 09:05:21PM +0200, Florian Mickler wrote:
> > On Wed, 2 Jun 2010 21:02:24 +1000
> > Neil Brown <neilb@...e.de> wrote:
> > > 
> > > And this decision (to block suspend) really needs to be made in the driver,
> > > not in userspace?
> > 
> > Well, it fits. The requirement is a direct consequence of the intimate
> > knowledge the driver has about the driven devices.
> 
> That is not really true. A driver does have intimate knowledge of the
> device, however it does not necessarily have an idea about the data read
> from the device. Consider the gpio_matrix driver: Arve says that it has
> to continue scanning matrix once first interrupt arrvies. But it really
> depends on what key has been pressed - if user pressed KEY_SUSPEND or
> KEY_POWER it cmight be better if we did not wait for key release but
> initiated the action right away. The decision on how system reacts to a
> key press does not belong to the driver but really to userspace.
>  

I can't follow the gpio_matrix_driver example, but your point is
obviously true. 
A device should never register a constraint because of the data it
handles. That belongs into userspace. Or wherever the data is
consumed. 

I'm obviously not trying to say that a network driver should block
suspend while I'm on facebook. Or unblock when visiting m$.com. That
would be absurd. 

But, there are of course places in the kernel, where some kernel code
listens to data. For example the packet-filtering. Or sysrq-keys.
But I don't know how that relates to suspend_blockers now... ? 

Mind if I rephrase the quote?
From: "Well, it fits. The requirement is a direct consequence of the
intimate knowledge the driver has about the driven devices." 
To: "It fits, when the requirement is a direct consequence of the
intimate knowledge the driver has about the driven devices."

Cheers,
Flo

p.s.: tsss.... language... what a broken concept. And yet we have to
work with it.
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