linux-kernel - Re: [PATCH] platform/chrome: cros_ec_typec: Handle NULL EC pointer during probe.

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Date:   Thu, 30 Apr 2020 09:17:03 -0700
From:   Prashant Malani <pmalani@...omium.org>
To:     Enric Balletbo i Serra <enric.balletbo@...labora.com>
Cc:     Daniil Lunev <dlunev@...omium.org>,
        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.

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);
> >>>>>