Date: Sun, 6 Jun 2004 21:34:02 +0200
From: Vojtech Pavlik <vojtech@suse.cz>
To: Pavel Machek <pavel@suse.cz>
Cc: Dmitry Torokhov <dtor_core@ameritech.net>, linux-kernel@vger.kernel.org
Subject: Re: locking in psmouse
Message-ID: <20040606193402.GA4291@ucw.cz>
References: <20040428213040.GA954@elf.ucw.cz> <200404282347.47411.dtor_core@ameritech.net> <20040429095830.GD390@elf.ucw.cz> <200404290740.18182.dtor_core@ameritech.net> <20040606174143.GA6561@ucw.cz> <20040606185158.GA3169@elf.ucw.cz>
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On Sun, Jun 06, 2004 at 08:51:59PM +0200, Pavel Machek wrote:
> Hi!
> 
> > > > > > psmouse-base.c does not have any locking. For example psmouse_command
> > > > > > could race with data coming from the mouse, resulting in problem. This
> > > > > > should fix it.
> > > > > 
> > > > > Although I am not arguing that locking might be needed in psmouse module I
> > > > > am somewhat confused how it will help in case of data stream coming from the
> > > > > mouse... If mouse sent a byte before the kernel issue a command then it will
> > > > > be delivered by KBC controller and will be processed by the interrupt handler,
> > > > > probably messing up detection process. That's why as soon as we decide that
> > > > > the device behind PS/2 port is some kind of mouse we disable the stream mode.
> > > > 
> > > > Does that mean that mouse can not talk while we are sending commands
> > > > to it? That would help a bit.
> > > > 
> > > 
> > > Yes, check psmouse_probe. As soon as PSMOUSE_CMD_RESET_DIS acknowledged mouse
> > > should cease sending motion data. That still leaves possibility of screwing up
> > > detection if you are moving mouse while psmouse doing PSMOUSE_CMD_GETID.
> > > But I don't think we can do much about it as we'd like to know that the device
> > > is some kind of a mouse before we start messing with it.
> > 
> > I've updated the atkbd_command/atkbd_interrupt mechanism so that even
> > bytes coming from the keyboard when we're issuing a command shouldn't
> > disturb us. I've tested by banging my head at the keyboard while
> > plugging it in. ;)
> > 
> > Something like that might be worth implementing for psmouse as well.
> 
> Well, psmouse case should be just converting int foo:1 into
> set_bit(&flags, BIT_FOO), no?

Not that easy. It wasn't as easy for atkbd either. This isn't just a
case of locking - it's making sure you always know whether the next byte
is data from the keyboard/mouse or a command response.

Only after getting the first ACK you can be sure that the keyboard/mouse
will not be sending any scancodes/movement data.

> But I guess autorepeat and higher layers of keyboard might be
> "interesting".

We'll get there ...

-- 
Vojtech Pavlik
SuSE Labs, SuSE CR
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