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Date:   Fri, 1 May 2020 10:15:18 +1000
From:   Daniil Lunev <dlunev@...omium.org>
To:     Prashant Malani <pmalani@...omium.org>
Cc:     Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>
Subject: Re: [PATCH] platform/chrome: cros_ec_typec: Handle NULL EC pointer
 during probe.

On the official revision of coreboot for hatch it doesn't even try to
load Type C. However it gives some warning messages from
cros-usbpd-notify-acpi about EC, So I wonder why the check of the same
type is not appropriate in the typec driver?

../chrome/cros_usbpd_notify.c

/* Get the EC device pointer needed to talk to the EC. */
ec_dev = dev_get_drvdata(dev->parent);
if (!ec_dev) {
/*
* We continue even for older devices which don't have the
* correct device heirarchy, namely, GOOG0003 is a child
* of GOOG0004.
*/
dev_warn(dev, "Couldn't get Chrome EC device pointer.\n");
}


# dmesg
...
[    8.513351] cros-ec-spi spi-PRP0001:02: EC failed to respond in time
[    8.722072] cros-ec-spi spi-PRP0001:02: EC failed to respond in time
[    8.729271] cros-ec-spi spi-PRP0001:02: Cannot identify the EC: error -110
[    8.736966] cros-ec-spi spi-PRP0001:02: cannot register EC,
fallback to spidev
[    8.767017] cros_ec_lpcs GOOG0004:00: Chrome EC device registered
[    8.807537] cros-usbpd-notify-acpi GOOG0003:00: Couldn't get Chrome
EC device pointer.
...

On Fri, May 1, 2020 at 2:17 AM Prashant Malani <pmalani@...omium.org> wrote:
>
> Hi Enric,
>
> On Thu, Apr 30, 2020 at 8:26 AM Enric Balletbo i Serra
> <enric.balletbo@...labora.com> wrote:
> >
> > Hi Prashant,
> >
> > On 30/4/20 2:43, Prashant Malani wrote:
> > > On Wed, Apr 29, 2020 at 5:38 PM Daniil Lunev <dlunev@...omium.org> wrote:
> > >>
> > >> [to make it appear on the mailing list as I didn't realize I was in
> > >> hypertext sending mode]
> > >>
> > >> On Thu, Apr 30, 2020 at 10:11 AM Daniil Lunev <dlunev@...omium.org> wrote:
> > >>>
> > >>> Hi Enric.
> > >>> I encountered the issue on a Hatch device when trying running 5.4 kernel on that. After talking to Prashant it seems that any device with coreboot built before a certain point (a particular fix for device hierarchy in ACPI tables of Chrome devices which happened in mid-April) will not be able to correctly initialize the driver and will get a kernel panic trying to do so.
> > >
> > > A clarifying detail here: This should not be seen in any current
> > > *production* device. No prod device firmware will carry the erroneous
> > > ACPI device entry.
> > >
> >
> > Thanks for the clarification. Then, I don't think we need to upstream this. This
> > kind of "defensive-programming" it's not something that should matter to upstream.
>
> Actually, on second thought, I am not 100% sure about this:
> Daniil, is the erroneous ACPI device on a *production* firmware for
> this device (I'm not sure about the vintage of that device's BIOS)?
>
> My apologies for the confusion, Enric and Daniil; but would be good to
> get clarification from Daniil.
>
> Best regards,
> >
> > Thanks,
> >  Enric
> >
> >
> > >>> Thanks,
> > >>> Daniil
> > >>>
> > >>> On Thu, Apr 30, 2020 at 7:58 AM Enric Balletbo i Serra <enric.balletbo@...labora.com> wrote:
> > >>>>
> > >>>> Hi Daniil,
> > >>>>
> > >>>> Thank you for the patch.
> > >>>>
> > >>>> On 28/4/20 3:02, Daniil Lunev wrote:
> > >>>>> Missing EC in device hierarchy causes NULL pointer to be returned to the
> > >>>>> probe function which leads to NULL pointer dereference when trying to
> > >>>>> send a command to the EC. This can be the case if the device is missing
> > >>>>> or incorrectly configured in the firmware blob. Even if the situation
> > >>>>
> > >>>> There is any production device with a buggy firmware outside? Or this is just
> > >>>> for defensive programming while developing the firmware? Which device is
> > >>>> affected for this issue?
> > >>>>
> > >>>> Thanks,
> > >>>>  Enric
> > >>>>
> > >>>>> occures, the driver shall not cause a kernel panic as the condition is
> > >>>>> not critical for the system functions.
> > >>>>>
> > >>>>> Signed-off-by: Daniil Lunev <dlunev@...omium.org>
> > >>>>> ---
> > >>>>>
> > >>>>>  drivers/platform/chrome/cros_ec_typec.c | 5 +++++
> > >>>>>  1 file changed, 5 insertions(+)
> > >>>>>
> > >>>>> diff --git a/drivers/platform/chrome/cros_ec_typec.c b/drivers/platform/chrome/cros_ec_typec.c
> > >>>>> index 874269c07073..30d99c930445 100644
> > >>>>> --- a/drivers/platform/chrome/cros_ec_typec.c
> > >>>>> +++ b/drivers/platform/chrome/cros_ec_typec.c
> > >>>>> @@ -301,6 +301,11 @@ static int cros_typec_probe(struct platform_device *pdev)
> > >>>>>
> > >>>>>       typec->dev = dev;
> > >>>>>       typec->ec = dev_get_drvdata(pdev->dev.parent);
> > >>>>> +     if (!typec->ec) {
> > >>>>> +             dev_err(dev, "Failed to get Cros EC data\n");
> > >>>>> +             return -EINVAL;
> > >>>>> +     }
> > >>>>> +
> > >>>>>       platform_set_drvdata(pdev, typec);
> > >>>>>
> > >>>>>       ret = cros_typec_get_cmd_version(typec);
> > >>>>>

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