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Date:   Fri, 12 Jun 2020 10:02:40 +0200
From:   Oleksij Rempel <o.rempel@...gutronix.de>
To:     Krzysztof Kozlowski <krzk@...nel.org>
Cc:     Fugang Duan <B38611@...escale.com>,
        Shawn Guo <shawnguo@...nel.org>,
        Sascha Hauer <s.hauer@...gutronix.de>,
        linux-kernel@...r.kernel.org, Gao Pan <b54642@...escale.com>,
        Oleksij Rempel <linux@...pel-privat.de>,
        Wolfram Sang <wsa@...nel.org>,
        NXP Linux Team <linux-imx@....com>,
        Pengutronix Kernel Team <kernel@...gutronix.de>,
        stable@...r.kernel.org, Fabio Estevam <festevam@...il.com>,
        linux-arm-kernel@...ts.infradead.org, linux-i2c@...r.kernel.org
Subject: Re: [PATCH] i2c: imx: Fix external abort on early interrupt

On Fri, Jun 12, 2020 at 09:38:15AM +0200, Krzysztof Kozlowski wrote:
> On Fri, Jun 12, 2020 at 07:51:14AM +0200, Oleksij Rempel wrote:
> > Hi Krzysztof,
> > 
> > thank you for your patch.
> > 
> > On Wed, Jun 10, 2020 at 03:46:42PM +0200, Krzysztof Kozlowski wrote:
> > > If interrupt comes early (could be triggered with CONFIG_DEBUG_SHIRQ),
> > > the i2c_imx_isr() will access registers before the I2C hardware is
> > > initialized.  This leads to external abort on non-linefetch on Toradex
> > > Colibri VF50 module (with Vybrid VF5xx):
> > > 
> > >     Unhandled fault: external abort on non-linefetch (0x1008) at 0x8882d003
> > >     Internal error: : 1008 [#1] ARM
> > >     Modules linked in:
> > >     CPU: 0 PID: 1 Comm: swapper Not tainted 5.7.0 #607
> > >     Hardware name: Freescale Vybrid VF5xx/VF6xx (Device Tree)
> > >       (i2c_imx_isr) from [<8017009c>] (free_irq+0x25c/0x3b0)
> > >       (free_irq) from [<805844ec>] (release_nodes+0x178/0x284)
> > >       (release_nodes) from [<80580030>] (really_probe+0x10c/0x348)
> > >       (really_probe) from [<80580380>] (driver_probe_device+0x60/0x170)
> > >       (driver_probe_device) from [<80580630>] (device_driver_attach+0x58/0x60)
> > >       (device_driver_attach) from [<805806bc>] (__driver_attach+0x84/0xc0)
> > >       (__driver_attach) from [<8057e228>] (bus_for_each_dev+0x68/0xb4)
> > >       (bus_for_each_dev) from [<8057f3ec>] (bus_add_driver+0x144/0x1ec)
> > >       (bus_add_driver) from [<80581320>] (driver_register+0x78/0x110)
> > >       (driver_register) from [<8010213c>] (do_one_initcall+0xa8/0x2f4)
> > >       (do_one_initcall) from [<80c0100c>] (kernel_init_freeable+0x178/0x1dc)
> > >       (kernel_init_freeable) from [<80807048>] (kernel_init+0x8/0x110)
> > >       (kernel_init) from [<80100114>] (ret_from_fork+0x14/0x20)
> > > 
> > > Additionally, the i2c_imx_isr() could wake up the wait queue
> > > (imx_i2c_struct->queue) before its initialization happens.
> > > 
> > > Fixes: 1c4b6c3bcf30 ("i2c: imx: implement bus recovery")
> > > Cc: <stable@...r.kernel.org>
> > > Signed-off-by: Krzysztof Kozlowski <krzk@...nel.org>
> > 
> > 
> > I assume register access is aborted, because the IP core clock is not
> > enabled. In this case we have bigger problem then just probe.
> 
> If by IP core clock you mean the clock which driver is getting, then
> answer is no. This clock is enabled.
> 
> > Since this driver support runtime power management, the clock will be
> > disabled as soon as transfer is done. It means, on shared interrupt, we
> > will get in trouble even if there is no active transfer.
> 
> The driver's runtime PM plays only with this one clock, so it seems
> you meant i2c_imx->clk. It is not this problem.
> 
> > 
> > So, probably the only way to fix it, is to check in i2c_imx_isr() if the
> > HW is expected to be active and register access should be save.
> 
> Checking in every interrupt whether the interrupt should be serviced
> based on some SW flag because HW might be disabled? That looks unusual,
> like a hack.
> 
> No, the interrupt should be registered when the driver and some other
> pieces of HW are ready to service it.

OK.
please make sure, irq is probed before calling
i2c_add_numbered_adapter(). This will trigger deferred probing of
slave devices. Since the irq handler will be added later, tx completion
of some requests will be lost or fail.

Regards,
Oleksij
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