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From:   Gwendal Grignou <gwendal@chromium.org>
Date:   Wed, 27 Feb 2019 10:34:07 -0800
Message-ID: <CAMHSBOXF_PtSTpcnVcJE7bMRA85TCqZdJL3Md4Z_Cd4Djjkw1A@mail.gmail.com>
Subject: Re: [PATCH] cros_ec: instantiate properly Intel ISH MCU device
To:     Enric Balletbo i Serra <enric.balletbo@collabora.com>
Cc:     Jett Rink <jettrink@chromium.org>,
        Guenter Roeck <groeck@google.com>,
        Rushikesh S Kadam <rushikesh.s.kadam@intel.com>,
        Lee Jones <lee.jones@linaro.org>,
        Benson Leung <bleung@chromium.org>,
        Guenter Roeck <groeck@chromium.org>,
        linux-kernel <linux-kernel@vger.kernel.org>,
        andriy.shevchenko@intel.com, Aaron Durbin <adurbin@google.com>,
        Duncan Laurie <dlaurie@google.com>
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On Wed, Feb 27, 2019 at 10:08 AM Enric Balletbo i Serra
<enric.balletbo@collabora.com> wrote:
>
> Hi Jett,
>
> Many thanks for the explanation.
>
> On 27/2/19 16:13, Jett Rink wrote:
> > The diagram you provided is correct.
> >
> > The ISH device is a MCU that can run general purpose code that is
> > located on the SoC. Typically the ISH collects sensor data and
> > processes it before giving it to the AP. The ISH HW can run any RTOS,
> > and in this scenario we are choosing to run the ECOS RTOS. In doing
> > so, we have access to the standard cros_ec command interface for
> > communication between the AP and ISH. This is helpful because we have
> > sensors drivers (Cros EC IIO Sensors) that depend on the cros_ec
> > command interface.
> >
> > The idea behind using a different sysfs path was to ensure that there
> > weren't any unintended consequences by adding a cros_ec device when
> > the ISH doesn't support most of the EC type tasks. Here are a few
> > examples:
> >  - Mosys tool is specifically trying to talk with an EC:
> > https://chromium.googlesource.com/chromiumos/platform/mosys/+/152a306a82009cd6ca68760b0902fc03781e0d5d/platform/daisy/ec.c#41
> >  - The ectool is specifically trying to talk with an EC:
> > https://chromium.googlesource.com/chromiumos/platform/ec/+/a3c27b39fa69f280a3728a5cf24de57a5d3ccb0d/util/ectool.c#8546
That's the default, we can override the name with --name option.
> >
> > At least on active project, there has already been confusion that the
> > normal ectool program doesn't work because the EC on the system is 3rd
> > party and does not support the normal cros_ec interface. This
> > confusion would compound if the ISH started presenting the cros_ec
> > interface and the ectool started talking to the ISH instead of the 3rd
> > party EC. Maybe we just need to modify ectool to make that situation
> > less confusing, but this is an example of the cross over using the
> > cros_ish device name is trying to avoid.
> >
>
> IMHO the problem with names is that is not really scalable, right now, we have
>
> /sys/class/chromeos/cros_ec
> /dev/cros_ec
>
> and
>
> /sys/class/chromeos/cros_pd
> /dev/cros_pd
>
> but looks like, apart from this, we will have
>
> /sys/class/chromeos/cros_ish
> /dev/cros_ish
>
> And a lot more: cros_fp, cros_tp, cros_scp, etc
>
>
> I was thinking in a solution more scalable where all the cros-ec are enumerated
> by an index, so is more generic. So in a system with 2 cros-ec you'll have
>
> /sys/class/chromeos/cros_ec0
> /dev/cros_ec0
>
> /sys/class/chromeos/cros_ec1
> /dev/cros_ec1
>
> ...
>
> In such case, from userspace point of view, when you open the device you can
> send the EC_CMD_GET_FEATURES and know which EC is under the device.
>
> One of the problems I see is that some old ECs (cros_pd I guess) doesn't
> implement that command, in such case maybe we can continue using the name to
> differentiate from other ECs.
>
> I'm unsure yet of the impact of this change though, so I'd like to listen
> Guenter and Benson opinions here :)

You're right, the cros_ names are based on what the EC provides.
cros_ec for generic EC, fp, tp for fingerprint, touch pad
respectively.
ish is for standalone sensor hub [it does not have to be Intel Sensor Hub].

ChromeOS user space tool are using the cros_XX names directly, like
biod is using cros_fp.

I agree the number of standalone EC in the system is increasing, but
it is still bounded.

Gwendal.


>
> Will this solution work for you? Do you see any problem?
>
>
> > At this point though, we will definitely follow the guidance of people
> > more experienced in kernel design. If using cros_ish as a device name
> > instead of cros_ec is actually not a good idea, then we can accept
> > that and move forward and try to see what the fallout is from
> > userspace tools.
> >
> > -Jett
> >
> >
> > On Wed, Feb 27, 2019 at 7:22 AM Enric Balletbo i Serra
> > <enric.balletbo@collabora.com> wrote:
> >>
> >> Hi,
> >>
> >> On 26/2/19 18:21, Jett Rink wrote:
> >>> We are specifically wanting userspace applications to not worry/confuse cros_ish
> >>> with a normal cros_ec. Adding an attribute instead of changing the path would
> >>> make it easy for userspace application to forget to check properly before
> >>> accessing the ish as an EC when it shouldn't.
> >>>
> >>> On Mon, Feb 25, 2019 at 4:37 PM Guenter Roeck <groeck@google.com
> >>> <mailto:groeck@google.com>> wrote:
> >>>
> >>>     On Mon, Feb 25, 2019 at 3:22 PM Jett Rink <jettrink@chromium.org
> >>>     <mailto:jettrink@chromium.org>> wrote:
> >>>
> >>>         A cros_ec and cros_ish device could both be present on the same system.
> >>>         We want to change the device path to ensure that drivers/code further up
> >>>         the stack does not get confuse the ISH with as an EC.
> >>>
> >>>         The ISH device can export a similar sysfs interface as they both use the
> >>>         same command interface for communication (although they will use
> >>>         different transport layers). The common cros code will detect certain
> >>>         EC_FEATURES and enable the correct subsystem based on the level of
> >>>         functionality the device supports. In the case of the ISH, the sensor
> >>>         subsystem will be enabled.
> >>>
> >>>     Seems to me it would make more sense to handle that difference with a sysfs
> >>>     attribute (instead of forcing each userspace application to support multiple
> >>>     sysfs paths).
> >>>
> >>
> >> Is still unclear to me what's that ISH device, so I'd appreciate if you can give
> >> some more background. Trying to understand the topology, makes sense that block
> >> diagram to you?
> >>
> >>
> >>        ---------------------------
> >>       |  User Space Applications  |
> >>        ---------------------------
> >>
> >> ----------------IIO ABI----------------
> >>
> >>        -----------------------------
> >>       |  CrOS EC IIO Sensor Drivers |
> >>        -----------------------------
> >>
> >>        --------------------------
> >>       |  CrOS EC over ISH Driver |
> >>        --------------------------
> >>
> >> ---------------- OS ------------------
> >>
> >>        --------------------------
> >>       |     CrOS EC Firmware     |
> >>        --------------------------
> >>
> >>        --------------------------
> >>       | ISH Hardware/Firmware    |
> >>        --------------------------
> >>
> >> So I'm right assuming that this CrOS EC will implement only the sensor features?
> >>
> >> And then, the system will have another CrOS EC implementing other features like
> >> RTC, USBPD-charger, etc?
> >>
> >> Apart from the sensors features, will the CrOS EC ISH implement other features?
> >>
> >> I'm a bit worried about the increasing way to use a particular name for
> >> different CrOS EC, actually we have only cros_ec and cros_pd. But in the
> >> chromeos kernels there is /dev/cros_fp, /dev/cros_tp, /dev/cros_ish,
> >> /dev/cros_scp and who knows how many more in the future. So I'm wondering if
> >> wouldn't be better use standard names, i.e /dev/cros_ec0, /dev/cros_ec1, etc. as
> >> userspace, for those cases, should be able to query the EC_FEATURE_ISH/FP/TP/SCP
> >> and know against which EC the device is attached.
> >>
> >> Cheers,
> >> Enric
> >>
> >>>     Guenter
> >>>
> >>>
> >>>         -Jett
> >>>
> >>>         On Sun, Feb 24, 2019 at 4:03 PM Guenter Roeck <groeck@google.com
> >>>         <mailto:groeck@google.com>> wrote:
> >>>
> >>>             On Sun, Feb 24, 2019 at 1:14 AM Rushikesh S Kadam
> >>>             <rushikesh.s.kadam@intel.com <mailto:rushikesh.s.kadam@intel.com>>
> >>>             wrote:
> >>>
> >>>                 Intel Integrated Sensor Hub (ISH) is also a MCU running EC
> >>>                 having feature bit EC_FEATURE_ISH. Instantiate it as a special
> >>>                 CrOS EC device with device name 'cros_ish'.
> >>>
> >>>
> >>>             The type of MCU doesn't really have to be reflected in the sysfs
> >>>             directory path. cros_ec uses different
> >>>             MCUs over time.
> >>>
> >>>             Will the new path exist in parallel with cros_ec (in other words,
> >>>             will there also be a stand-alone EC in the same system) ? Does it
> >>>             have different or the same sysfs attributes as cros_ec ?
> >>>
> >>>             Also,, what is the impact on userspace ?
> >>>
> >>>             Thanks,
> >>>             Guenter
> >>>
> >>>                 Signed-off-by: Rushikesh S Kadam <rushikesh.s.kadam@intel.com
> >>>                 <mailto:rushikesh.s.kadam@intel.com>>
> >>>                 ---
> >>>                  drivers/mfd/cros_ec_dev.c            | 10 ++++++++++
> >>>                  include/linux/mfd/cros_ec.h          |  1 +
> >>>                  include/linux/mfd/cros_ec_commands.h |  2 ++
> >>>                  3 files changed, 13 insertions(+)
> >>>
> >>>                 diff --git a/drivers/mfd/cros_ec_dev.c b/drivers/mfd/cros_ec_dev.c
> >>>                 index 2d0fee4..be499b8 100644
> >>>                 --- a/drivers/mfd/cros_ec_dev.c
> >>>                 +++ b/drivers/mfd/cros_ec_dev.c
> >>>                 @@ -414,6 +414,16 @@ static int ec_device_probe(struct
> >>>                 platform_device *pdev)
> >>>                         device_initialize(&ec->class_dev);
> >>>                         cdev_init(&ec->cdev, &fops);
> >>>
> >>>                 +       /* check whether this is actually a Intel ISH rather
> >>>                 than an EC */
> >>>                 +       if (cros_ec_check_features(ec, EC_FEATURE_ISH)) {
> >>>                 +               dev_info(dev, "Intel ISH MCU detected.\n");
> >>>                 +               /*
> >>>                 +                * Help userspace differentiating ECs from ISH MCU,
> >>>                 +                * regardless of the probing order.
> >>>                 +                */
> >>>                 +               ec_platform->ec_name = CROS_EC_DEV_ISH_NAME;
> >>>                 +       }
> >>>                 +
> >>>                         /*
> >>>                          * Add the class device
> >>>                          * Link to the character device for creating the /dev entry
> >>>                 diff --git a/include/linux/mfd/cros_ec.h
> >>>                 b/include/linux/mfd/cros_ec.h
> >>>                 index de8b588..00c5765 100644
> >>>                 --- a/include/linux/mfd/cros_ec.h
> >>>                 +++ b/include/linux/mfd/cros_ec.h
> >>>                 @@ -24,6 +24,7 @@
> >>>
> >>>                  #define CROS_EC_DEV_NAME "cros_ec"
> >>>                  #define CROS_EC_DEV_PD_NAME "cros_pd"
> >>>                 +#define CROS_EC_DEV_ISH_NAME "cros_ish"
> >>>
> >>>                  /*
> >>>                   * The EC is unresponsive for a time after a reboot command.  Add a
> >>>                 diff --git a/include/linux/mfd/cros_ec_commands.h
> >>>                 b/include/linux/mfd/cros_ec_commands.h
> >>>                 index fc91082..9276c3c 100644
> >>>                 --- a/include/linux/mfd/cros_ec_commands.h
> >>>                 +++ b/include/linux/mfd/cros_ec_commands.h
> >>>                 @@ -856,6 +856,8 @@ enum ec_feature_code {
> >>>                         EC_FEATURE_RTC = 27,
> >>>                         /* EC supports CEC commands */
> >>>                         EC_FEATURE_CEC = 35,
> >>>                 +       /* The MCU is an Intel Integrated Sensor Hub */
> >>>                 +       EC_FEATURE_ISH = 40,
> >>>                  };
> >>>
> >>>                  #define EC_FEATURE_MASK_0(event_code) (1UL << (event_code % 32))
> >>>                 --
> >>>                 1.9.1
> >>>