linux-kernel - Re: [PATCH v5] platform: cros_ec: Query EC protocol version if EC transitions between RO/RW

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Date:   Mon, 3 Feb 2020 13:18:51 +0100
From:   Marek Szyprowski <m.szyprowski@...sung.com>
To:     Enric Balletbo Serra <eballetbo@...il.com>
Cc:     Yicheng Li <yichengli@...omium.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Benson Leung <bleung@...omium.org>,
        Gwendal Grignou <gwendal@...omium.org>,
        Tomasz Figa <tfiga@...omium.org>,
        Linux Samsung SOC <linux-samsung-soc@...r.kernel.org>
Subject: Re: [PATCH v5] platform: cros_ec: Query EC protocol version if EC
 transitions between RO/RW

Hi Enric

On 03.02.2020 10:33, Enric Balletbo Serra wrote:
> Missatge de Marek Szyprowski <m.szyprowski@...sung.com> del dia dv.,
> 31 de gen. 2020 a les 8:41:
>> On 07.01.2020 23:06, Yicheng Li wrote:
>>> RO and RW of EC may have different EC protocol version. If EC transitions
>>> between RO and RW, but AP does not reboot (this is true for fingerprint
>>> microcontroller / cros_fp, but not true for main ec / cros_ec), the AP
>>> still uses the protocol version queried before transition, which can
>>> cause problems. In the case of fingerprint microcontroller, this causes
>>> AP to send the wrong version of EC_CMD_GET_NEXT_EVENT to RO in the
>>> interrupt handler, which in turn prevents RO to clear the interrupt
>>> line to AP, in an infinite loop.
>>>
>>> Once an EC_HOST_EVENT_INTERFACE_READY is received, we know that there
>>> might have been a transition between RO and RW, so re-query the protocol.
>>>
>>> Change-Id: I49a51cc10d22a4ab9e75204a4c0c8819d5b3d282
>>> Signed-off-by: Yicheng Li <yichengli@...omium.org>
>> This patch landed recently in linux-next as commit
>> 241a69ae8ea8e2defec751fe55dac1287aa044b8. Sadly, it causes following
>> kernel oops on any key press on Samsung Exynos-based Chromebooks (Snow,
>> Peach-Pit and Peach-Pi):
> Many thanks for report the issue, we will take a look ASAP and revert
> this commit meanwhile.

Simply removing the BUG_ON() from cros_ec_get_host_event() function 
fixes the issue, but I don't know the protocol details to judge if this 
is the correct way of fixing it.

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland