linux-kernel - Re: [PATCH] ANDROID: usb: core: Send uevent when USB TOPO layer over 6

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Message-ID: <CADRPvQtbbxKhvmE1OZ=GRSmfejk5tXYADo=jw52EQdkj1nN78w@mail.gmail.com>
Date:   Fri, 5 Mar 2021 15:17:37 +0800
From:   Chien Kun Niu <rickyniu@...gle.com>
To:     Greg KH <gregkh@...uxfoundation.org>
Cc:     stern@...land.harvard.edu, erosca@...adit-jv.com,
        gustavoars@...nel.org, a.darwish@...utronix.de, oneukum@...e.com,
        Kyle Tso <kyletso@...gle.com>, linux-usb@...r.kernel.org,
        linux-kernel@...r.kernel.org, James Wei <jameswei@...gle.com>
Subject: Re: [PATCH] ANDROID: usb: core: Send uevent when USB TOPO layer over 6

Greg KH <gregkh@...uxfoundation.org> 於 2021年3月3日 週三 下午5:10寫道：
>
> On Wed, Mar 03, 2021 at 05:03:25PM +0800, Chien Kun Niu wrote:
> > Hi , Greg
> >
> > What tool will "catch" this?  Where is that code located at?
> > => I prepare merge the code to Android phone , so I used Android HLOS
> > to catch this uevent.
>
> Very odd quoting style, perhaps you might want to read up on how to do
> this properly at:
>         https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
>
> > uevents are not for stuff like this, you are trying to send "error
> > conditions" to userspace, please use the "proper" interfaces like this
> > and not abuse existing ones.
> > => Sorry , I am not sure what is the "proper" interfaces your mean.
> >      Could you please give me more description?
>
> How does the kernel normally send error conditions that it detects in
> hardware to userspace?
>

I will create a sysfs attribute to record the hub status.
If there is a new hub with over 6 USB TOPO layer connected, I will use
the sysfs_notify to send the "error conditions" to userspace.
Is it a proper interfaces to delivery "error conditions"?

> > You just created a whole new sysfs class with no Documentation/ABI/
> > update?
> > => Yes, I will add it.
> >
> > Wait, how did you even test this code?  This will not work if you have
> > more than one hub in the system at a single time, right?
> > => I build the test build which flash in Android phone and connect
> > several hubs to try it.
> >      When the new hub which met MAX_TOPO_LEVEL connected , it sent
> > notify to user space.
> >
> > Phone ------↓
> >                  hub ------↓
> >                              hub ------↓
> >                                            ...------↓
> >                                                     hub
> >
> >      if (hdev->level == MAX_TOPO_LEVEL) {
> >                 dev_err(&intf->dev,
> >                         "Unsupported bus topology: hub nested too deep\n");
> >                 hub_over_tier();
> >                 return -E2BIG;
> >      }
> >
>
> But you only have a single hub variable, and a huge memory leak, did you
> not detect that in your testing?
>
> > So, proof that this works?  How did you test this?
> > => I use the Pixel phone to verify the code , the framework received
> > the uevent when the last connected hub over "MAX_TOPO_LEVEL".
>
> Try it on a desktop as well, with many hubs and see what happens :(
>
> > Also, you have a memory leak in this submission :(
> > => Do you mean I should add device_destroy here ?
>
> What do you think should be done?
>
> >
> > hub_device =
> > device_create(hub_class, NULL, MKDEV(0, 0), NULL, "usb_hub");
> > +if (IS_ERR(hub_device))
> > +               return PTR_ERR(hub_device);
> >
> > void usb_hub_cleanup(void)
> > {
> > +if (!IS_ERR(hub_device))
> > +device_destroy(hub_class, hub_device->devt);
> >
> > if (!IS_ERR(hub_class))
> > class_destroy(hub_class);
>
> I don't think you are understanding that you can have multiple hubs in
> the system at the same time :(
>
> thanks,
>
> greg k-h

Thanks,

Chien Kun Niu