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

[Jeffrey Hugo]

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.

--
Jeffrey Hugo
Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.