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

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Date:   Thu, 30 Apr 2020 17:26:38 +0200
From:   Enric Balletbo i Serra <enric.balletbo@...labora.com>
To:     Prashant Malani <pmalani@...omium.org>,
        Daniil Lunev <dlunev@...omium.org>
Cc:     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 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.

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);
>>>>>