RE: [PATCH v10 0/6] Introduced new Cadence USBSS DRD Driver.

[Pawel Laszczak]

Hi, 

>On Mon 2019-07-22 13:56:44, Pavel Machek wrote:
>> Hi!
>>
>> > > >> This patch introduce new Cadence USBSS DRD driver to linux kernel.
>> > > >>
>> > > >> The Cadence USBSS DRD Controller is a highly configurable IP Core which
>> > > >> can be instantiated as Dual-Role Device (DRD), Peripheral Only and
>> > > >> Host Only (XHCI)configurations.
>> > > >
>> > > >I see you are using debugfs to select between DRD, peripheral-onlyh and XHCI...
>> > > >
>> > > >Is that good idea?
>> > >
>> > > Yes driver allows selecting dr_mode by debugfs. Controller also support such functionality
>> > > so I don't understand why would it not be a good idea.
>> > >
>> > > I personally use this for testing but it can be used to limit controller functionality without
>> > > recompiling kernel.
>> >
>> > debugfs is ONLY for debugging, never rely on it being enabled, or
>> > mounted, on a system in order to have any normal operation happen.
>> >
>> > So for testing, yes, this is fine.  If this is going to be the normal
>> > api/interface for how to control this driver, no, that is not acceptable
>> > at all.
>>
>> It makes a lot of sense for end-user to toggle this... for example
>> when he is lacking right cable for proper otg detection. As it is
>> third driver offering this functionality, I believe we should stop
>> treating it as debugging.
>
>At least renesas usb controller seems to have variables in sysfs:
>drivers/phy/renesas/phy-rcar-gen3-usb2.c : functions role_show and
>role_store. See also
>Documentation/ABI/testing/sysfs-platform-phy-rcar-gen3-usb2 .
>
>I believe this driver should do same.
>

CDNS3 driver use the role framework and also has such variable defined 
in role switch framework.

https://elixir.bootlin.com/linux/latest/source/drivers/usb/roles/class.c

Regards,
Pawel