linux-kernel - Re: [PATCH v3 1/4] mfd: cros_ec: Get rid of cros_ec_check_features from cros_ec

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Message-ID: <CAFqH_52FwqJudZ9mYPotaX=GvA11JrpaYEKmZWwJJYWe=DZwMQ@mail.gmail.com>
Date:   Thu, 20 Jul 2017 08:31:18 +0200
From:   Enric Balletbo Serra <eballetbo@...il.com>
To:     Lee Jones <lee.jones@...aro.org>
Cc:     Gwendal Grignou <gwendal@...omium.org>,
        Enric Balletbo i Serra <enric.balletbo@...labora.com>,
        Jonathan Cameron <jic23@...nel.org>,
        Benson Leung <bleung@...omium.org>,
        Javier Martinez Canillas <martinez.javier@...il.com>,
        Guenter Roeck <groeck@...omium.org>,
        Linux Kernel <linux-kernel@...r.kernel.org>,
        linux-iio@...r.kernel.org, rtc-linux@...glegroups.com
Subject: Re: [PATCH v3 1/4] mfd: cros_ec: Get rid of cros_ec_check_features
 from cros_ec_dev.

Lee,

2017-07-18 11:19 GMT+02:00 Lee Jones <lee.jones@...aro.org>:
> On Mon, 17 Jul 2017, Enric Balletbo Serra wrote:
>
>> Hi Gwendal,
>>
>> 2017-07-13 22:33 GMT+02:00 Gwendal Grignou <gwendal@...omium.org>:
>> > On Wed, Jul 12, 2017 at 3:13 AM, Enric Balletbo i Serra
>> > <enric.balletbo@...labora.com> wrote:
>> >> The cros_ec_dev driver should be used only to expose the Chrome OS Embedded
>> >> Controller to user-space and should not be used to add MFD devices by
>> >> calling mfd_add_devices. This patch moves this logic to the MFD cros_ec
>> >> driver and removes the MFD bits from the character device driver. Also
>> >> makes independent the IIO driver from the character device as also has no
>> >> sense.
>> >
>> > cros_ec_dev serves another purpose: it allows to represent an EC that
>> > does not have a cros_ec structure. It happens when there are several
>> > EC in a chromebook, and one EC is connected through another EC.
>> > One example is Samus (Pixel 2): where we have:
>> >
>> > (main SOC, Application Processor) AP --> (main Embedded Controller) EC
>> > ---> (Power Delivery [PD}) EC
>> >
>> > We  access to the PD EC via pass-through commands through the main EC.
>> > Each EC has a cros_ec_dev structure, but only the main EC as a
>> > cros_ec_device structure (I will forever regret the structure names).
>> >
>> > Now form the AP point of view, both ECs use the same protocol. That
>> > why the sensors and other devcies that are registered by looking at
>> > the feature fields are registered with cros_ec_dev as their parent.
>> > Other devices that are registered from the device tree, predating the
>> > feature field support, are registered with cros_ec_device as their
>> > parent.
>> >
>>
>> Interesting I didn't know that. So are you saying that this patch will
>> break support for devices like Pixel 2? I tested the patches on
>> various devices but not on Pixel 2 so could be.
>
> Does this affect the rest of the series?
>

Yes, because this patch moves cros_ec_check_features from char dev driver...

> Or should I review/apply as usual?
>

Please, hold on while I figure out what's exactly the problem with
Samus. Sorry for the noise.

Cheers,
 Enric

> --
> Lee Jones
> Linaro STMicroelectronics Landing Team Lead
> Linaro.org │ Open source software for ARM SoCs
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