Re: [PATCH v2 0/9] Add support for Microsoft Surface System Aggregator Module

[Maximilian Luz]

On 12/6/20 11:43 AM, Hans de Goede wrote:
> Hi,
>
> On 12/6/20 11:33 AM, Maximilian Luz wrote:
> > On 12/6/20 10:06 AM, Leon Romanovsky wrote:> On Sun, Dec 06, 2020 at 05:58:32PM +0900, Blaž Hrastnik wrote:
> > > > > > More on that, the whole purpose of proposed interface is to debug and
> > > > > > not intended to be used by any user space code.
> > > > >
> > > > > The purpose is to provide raw access to the Surface Serial Hub protocol,
> > > > > just like we provide raw access to USB devices and have hidraw devices.
> > > > >
> > > > > So this goes a litle beyond just debugging; and eventually the choice
> > > > > may be made to implement some functionality with userspace drivers,
> > > > > just like we do for some HID and USB devices.
> > > > >
> > > > > Still I agree with you that adding new userspace API is something which
> > > > > needs to be considered carefully. So I will look at this closely when
> > > > > reviewing this set.
> > > >
> > > > To add to that: this was previously a debugfs interface but was moved to misc after review on the initial RFC:
> > > > https://lkml.org/lkml/2020/9/24/96
> > >
> > > There is a huge difference between the suggestion and final implementation.
> > >
> > > Greg suggested to add new debug module to the drivers/misc that will
> > > open char device explicitly after user loaded that module to debug this
> > > hub. However, the author added full blown char device as a first citizen
> > > that has all not-break-user constrains.
> >
> > This module still needs to be loaded explicitly.
>
> Good then I really do not see a problem with this.
>
> > And (I might be wrong
> > about this) the "not-break-user constraints" hold as soon as I register
> > a misc device at all, no?
>
> Correct.
>
> > So I don't see how this is a) any different
> > than previously discussed with Greg and b) how the uapi header now
> > introduces any not-break-user constraints that would not be there
> > without it.
> >
> > This interface is intended as a stable interface. That's something that
> > I committed to as soon as I decided to implement this via a misc-device.
> >
> > Sure, I can move the definitions in the uapi header to the module
> > itself, but I don't see any benefit in that.
>
> Right, if we are going to use a misc chardev for this, then the
> correct thing to do is to put the API bits for that chardev under
> include/uapi.
>
> It would still be good if you can provide a pointer to some userspace
> tools using this new API; and for the next version maybe add that
> pointer to the commit message

Right, I will add that to the commit message. I just linked you the
scripts in my other response, but here again for completeness:

  https://github.com/linux-surface/surface-aggregator-module/tree/master/scripts/ssam

While I'm not using the header directly (the scripts are written in
python) I still think uapi is the right place to put this (please
correct me if I'm wrong). Not putting them there seems to be needless
obfuscating to me.

Regards,
Max