linux-kernel - Re: [PATCH v3 1/1] i2c: qcom-geni: Provide an option to disable DMA processing

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Message-ID: <3458ed2a-ae49-b46b-3e89-ce039a2749b4@axentia.se>
Date:   Thu, 5 Sep 2019 13:58:24 +0000
From:   Peter Rosin <peda@...ntia.se>
To:     Wolfram Sang <wsa@...-dreams.de>, Lee Jones <lee.jones@...aro.org>
CC:     "alokc@...eaurora.org" <alokc@...eaurora.org>,
        "agross@...nel.org" <agross@...nel.org>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "mark.rutland@....com" <mark.rutland@....com>,
        "bjorn.andersson@...aro.org" <bjorn.andersson@...aro.org>,
        "vkoul@...nel.org" <vkoul@...nel.org>,
        "linux-arm-kernel@...ts.infradead.org" 
        <linux-arm-kernel@...ts.infradead.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-i2c@...r.kernel.org" <linux-i2c@...r.kernel.org>,
        "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>
Subject: Re: [PATCH v3 1/1] i2c: qcom-geni: Provide an option to disable DMA
 processing

On 2019-09-05 15:49, Wolfram Sang wrote:
> Hi Lee,
> 
> I understand you are in a hurry, but please double check before
> sending...

Linus indicated that an rc8 is coming up, which should provide an extra week.
https://lwn.net/Articles/798152/

> On Thu, Sep 05, 2019 at 11:22:47AM +0100, Lee Jones wrote:
>> We have a production-level laptop (Lenovo Yoga C630) which is exhibiting
>> a rather horrific bug.  When I2C HID devices are being scanned for at
>> boot-time the QCom Geni based I2C (Serial Engine) attempts to use DMA.
>> When it does, the laptop reboots and the user never sees the OS.
>>
>> The beautiful thing about this approach is that, *if* the Geni SE DMA
>> ever starts working, we can remove the C code and any old properties
>> left in older DTs just become NOOP.  Older kernels with newer DTs (less
>> of a priority) *still* will not work - but they do not work now anyway.
> 
> ... becasue this paragraph doesn't fit anymore. Needs to be reworded.
> 
>>
>> Fixes: 8bc529b25354 ("soc: qcom: geni: Add support for ACPI")
> 
> As said in the other thread, I don't get it, but this is not a show
> stopper for me.

WAG: because ACPI made some driver load at all, and when it
did it something started happening which crashed some machines.

Cheers,
Peter