Re: [PATCH] PCMCIA: prevent auto insert during resume.

[Russell King <rmk+lkml@arm.linux.org.uk>]

On Fri, Oct 26, 2007 at 06:54:00PM +0200, Rodolfo Giometti wrote:
> On Fri, Oct 26, 2007 at 05:36:51PM +0100, Russell King wrote:
> > On Fri, Oct 26, 2007 at 06:27:06PM +0200, Rodolfo Giometti wrote:
> > > On Fri, Oct 26, 2007 at 05:02:06PM +0100, Russell King wrote:
> > > > When you bring the battery device out of resume, and you've inserted a
> > > > card, you want it to be detected.  Your change means you have to wait
> > > > until the system has finished resuming before you plug the card in,
> > > > which practically is a pain in the butt and actually leads to user
> > > > errors.  IOW:
> > > > 
> > > > "I plugged my wireless card in after I pressed the power button, why
> > > > wasn't it detected?"
> > > 
> > > My patch doesn't affect the power on sequence, just the resume
> > > one.
> > 
> > On a lot of devices, the "power button" is the resume button.  When you
> > "turn it off" it suspends, and when you "turn it on" it resumes.
> 
> I see. My device has two buttons.
> 
> However even in this case, if you never eject the device, then switch
> off (sleep), change the device into the slot and then power on (wake
> up), with my patch everything continues to work as before.
> 
> The differences come up only if you eject the device before power off.

Yes and it's extremely irritating that a plugged in card doesn't get
detected.

> > > Also if you didn't eject the socket, at resume the device will be
> > > powered up again, my patch just prevents that a pre-powered off device
> > > to be turned on at resume time.
> > > 
> > > However you should consider that some embedded systems have fixed
> > > PCMCIA devices that can't be removed so there are no reasons to detect
> > > them after resume, nobody can change them. :)
> > > 
> > > Also battery powered devices can go very frequently to sleep and the
> > > current behavior force the user to switch off the unused device each
> > > time the system resumes from sleep.
> > 
> > I realise that.  I do work on embedded devices, and this behaviour is
> > explicitly there to support embedded devices.
> > 
> > I've suggested a workable solution to you which allows both of us to
> > have the behaviour we both desire from the system.  That sounds like
> > a negotiated solution to me...
> 
> Do you mean to switch off the socket from userland? It could be a
> solution but in this case the device is powered on each time even if
> for a short delay...

If it's a permanent device, and you've powered it down via pccardctl,
then you've powered it down from userland.  So record that it's been
powered down from userland.  Then, on resume, if it's been powered down
from userland, don't try to re-power it on resume.

Is that clearer?

> Maybe we can add an entry into sysfs? Or just a module parameter? So
> developers can choose their preferred behaviour. :)

Or that - probably a sysfs attribute on the pcmcia socket would be
better.

-- 
Russell King
 Linux kernel    2.6 ARM Linux   - http://www.arm.linux.org.uk/
 maintainer of:
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