linux-kernel - Re: [PATCH] staging: Platform device tester

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Date:	Tue, 13 Aug 2013 19:55:12 +0100
From:	Russell King - ARM Linux <linux@....linux.org.uk>
To:	Pantelis Antoniou <panto@...oniou-consulting.com>
Cc:	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Tony Lindgren <tony@...mide.com>,
	Benoît Coussno <b-cousson@...com>,
	Paul Walmsley <paul@...an.com>,
	Sourav Poddar <sourav.poddar@...com>,
	Russ Dill <Russ.Dill@...com>, Felipe Balbi <balbi@...com>,
	Koen Kooi <koen@...cuitco.com>, linux-omap@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] staging: Platform device tester - Allow removal

On Tue, Aug 13, 2013 at 09:42:27PM +0300, Pantelis Antoniou wrote:
> But creation just crashes.
> 
> > root@...glebone:/sys/bus/platform/drivers/omap_i2c# echo 4819c000.i2c >bind   
> > [  145.053929] Unable to handle kernel NULL pointer dereference at virtual address 00000001
> > [  145.062651] pgd = ca8c0000
> > [  145.065507] [00000001] *pgd=8f437831, *pte=00000000, *ppte=00000000
> > [  145.072163] Internal error: Oops: 17 [#1] SMP ARM
> > [  145.077105] Modules linked in: ipv6 autofs4
> > [  145.081537] CPU: 0 PID: 301 Comm: sh Not tainted 3.11.0-rc5-00125-g3b988fb #146
> > [  145.089222] task: cf5b5580 ti: cf464000 task.ti: cf464000
> > [  145.094918] PC is at omap_i2c_runtime_suspend+0x10/0xb4
> > [  145.100408] LR is at omap_i2c_runtime_suspend+0x8/0xb4

Well then, what you have here is a bug in the way that OMAP re-uses the
platform device stuff - and that _does_ need fixing somehow.

The problem is that i2c_dev->regs is NULL at the point where
pm_runtime_set_autosuspend_delay() is called, which as autosuspend
is still set from the time that the device was unbound, it means that
this triggers an immediate suspend.

I suspect that:

        pm_runtime_set_autosuspend_delay(dev->dev, OMAP_I2C_PM_TIMEOUT);
        pm_runtime_use_autosuspend(dev->dev);

should be moved later in the probe function, after the switch (scheme)
block.
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