linux-kernel - 答复: [PATCH] bus: mhi: core: Introduce sysfs ul chan id for mhi chan device

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Date:   Wed, 28 Oct 2020 01:18:27 +0000
From:   Carl Yin(殷张成) <carl.yin@...ctel.com>
To:     Hemant Kumar <hemantk@...eaurora.org>,
        Jeffrey Hugo <jhugo@...eaurora.org>,
        "manivannan.sadhasivam@...aro.org" <manivannan.sadhasivam@...aro.org>,
        "sfr@...b.auug.org.au" <sfr@...b.auug.org.au>
CC:     "linux-arm-msm@...r.kernel.org" <linux-arm-msm@...r.kernel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "Naveen Kumar" <naveen.kumar@...ctel.com>
Subject: 答复: [PATCH] bus: mhi: core: Introduce sysfs ul chan id for mhi chan device

Hi Jeffery and Hemant:

On Wednesday, October 28, 2020 6:44 AM, hemantk wrote:
> On 10/27/20 8:06 AM, Jeffrey Hugo wrote:
> Hi Carl,
> 
> On 10/27/20 8:06 AM, Jeffrey Hugo wrote:
> > On 10/27/2020 3:43 AM, carl.yin@...ctel.com wrote:
> >> From: "carl.yin" <carl.yin@...ctel.com>
> >>
> >> User space software like ModemManager can identify the function of
> >> the mhi chan device by ul_chan_id.
> >>
> >> Signed-off-by: carl.yin <carl.yin@...ctel.com>
> >> ---
> >>   Documentation/ABI/stable/sysfs-bus-mhi | 10 ++++++++++
> >>   drivers/bus/mhi/core/init.c            | 15 +++++++++++++++
> >>   2 files changed, 25 insertions(+)
> >>
> >> diff --git a/Documentation/ABI/stable/sysfs-bus-mhi
> >> b/Documentation/ABI/stable/sysfs-bus-mhi
> >> index ecfe766..6d52768 100644
> >> --- a/Documentation/ABI/stable/sysfs-bus-mhi
> >> +++ b/Documentation/ABI/stable/sysfs-bus-mhi
> >> @@ -19,3 +19,13 @@ Description:    The file holds the OEM PK Hash
> >> value of the endpoint device
> >>           read without having the device power on at least once, the
> >> file
> >>           will read all 0's.
> >>   Users:        Any userspace application or clients interested in
> >> device info.
> >> +
> >> +What:        /sys/bus/mhi/devices/.../ul_chan_id
> >> +Date:        November 2020
> >> +KernelVersion:    5.10
> >> +Contact:    Carl Yin <carl.yin@...ctel.com>
> >> +Description:    The file holds the uplink chan id of the mhi chan
> >> device.
> >> +        User space software like ModemManager can identify the
> >> function of
> >> +        the mhi chan device. If the mhi device is not a chan device,
> >> +        eg mhi controller device, the file read -1.
> >> +Users:        Any userspace application or clients interested in
> >> device info.
> >> diff --git a/drivers/bus/mhi/core/init.c
> >> b/drivers/bus/mhi/core/init.c index c6b43e9..ac4aa5c 100644
> >> --- a/drivers/bus/mhi/core/init.c
> >> +++ b/drivers/bus/mhi/core/init.c
> >> @@ -105,9 +105,24 @@ static ssize_t oem_pk_hash_show(struct device
> >> *dev,
> >>   }
> >>   static DEVICE_ATTR_RO(oem_pk_hash);
> >> +static ssize_t ul_chan_id_show(struct device *dev,
> >> +                struct device_attribute *attr,
> >> +                char *buf)
> >> +{
> >> +    struct mhi_device *mhi_dev = to_mhi_device(dev);
> >> +    int ul_chan_id = -1;
> >> +
> >> +    if (mhi_dev->ul_chan)
> >> +        ul_chan_id = mhi_dev->ul_chan_id;
> >> +
> >> +    return snprintf(buf, PAGE_SIZE, "%d\n", ul_chan_id); } static
> >> +DEVICE_ATTR_RO(ul_chan_id);
> >> +
> >>   static struct attribute *mhi_dev_attrs[] = {
> >>       &dev_attr_serial_number.attr,
> >>       &dev_attr_oem_pk_hash.attr,
> >> +    &dev_attr_ul_chan_id.attr,
> >>       NULL,
> >>   };
> >>   ATTRIBUTE_GROUPS(mhi_dev);
> >>
> >
> > NACK
> >
> > Channel ID is a device specific detail.  Userspace should be basing
> > decisions on the channel name.
> >
> I agree with Jeff, why do you need to know the channel id, if you need to poll for
> any device node to get created you can try to open the device node from user
> space and wait until the device gets opened.
> Are you trying to wait for EDL channels to get started using UCI ?
[carl.yin] In my opinion, mhi chan id is something like 'bInterfaceNumber' of USB device.
A USB device and several USB interfaces, and a mhi devices have 128 mhi chans.
Chan id is a physical attribute of one mhi chan.

Next is the udev info of one mhi chan:
# udevadm info -a /dev/mhi_0000\:03\:00.0_EDL
  looking at parent device '/devices/pci0000:00/0000:00:1d.0/0000:03:00.0/0000:03:00.0_EDL':
    KERNELS=="0000:03:00.0_EDL"
    SUBSYSTEMS=="mhi"
    DRIVERS=="mhi_uci"
    ATTRS{serial_number}=="Serial Number: 2644481182"
    ATTRS{ul_chan_id}=="34"

If no ul_chan_id, the udev ruler will be ' KERNEL=="*_EDL" '
With ul_chan_id, the udev ruler will be ' ATTRS{ul_chan_id}=="34"'
I think the latter is more better.

> 
> Thanks,
> Hemant
> --
> The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum, a
> Linux Foundation Collaborative Project