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

[Carl Yin(殷张成)]

Hi Jeffrey:

On October 28, 2020 10:18 PM, jhugo wrote:
> On 10/27/2020 7:18 PM, Carl Yin(殷张成) wrote:
> > 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@xxxxxxxxxxx wrote:
> >>>> From: "carl.yin" <carl.yin@xxxxxxxxxxx>
> >>>>
> >>>> 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@xxxxxxxxxxx>
> >>>> ---
> >>>>    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@xxxxxxxxxxx>
> >>>> +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" '
> 
> I have several usecases where this works just fine today.
> 
> > With ul_chan_id, the udev ruler will be ' ATTRS{ul_chan_id}=="34"'
> 
> This breaks when there is some new device that has the EDL channel on some
> different chan_id, like 7.  The above does not.  Additionally if there is a
> different device that is using chan_id 34 for a different purpose, say Diag, then
> your udev rule also breaks.
> 
> The name of the channel is the interface to the channel.  Not the chan_id.  This
> holds true within the kernel, and should be the same for userspace.  I still
> oppose this change.
[carl.yin] ok, I agree that chan id is not a good and necessary choice.
	ModemManager also work well with ' KERNEL=="mhi_*_<chan name>"'.
> 
> --
> Jeffrey Hugo
> Qualcomm Technologies, Inc. is a member of the Code Aurora Forum, a Linux
> Foundation Collaborative Project.