[PATCH 4/7] phy: meson: add USB2 PHY support for Meson8b and GXBB

[Martin Blumenstingl]

On Wed, Sep 14, 2016 at 10:37 AM, Philipp Zabel <p.zabel at pengutronix.de> wrote:
> Am Dienstag, den 13.09.2016, 17:59 -0700 schrieb Kevin Hilman:
>> Martin Blumenstingl <martin.blumenstingl at googlemail.com> writes:
>>
>> > On Tue, Sep 13, 2016 at 5:28 PM, Philipp Zabel <p.zabel at pengutronix.de> wrote:
>>
>> [...]
>>
>> >>> I added Philipp and Hans to this thread - maybe they can comment on this.
>> >>> To sum it up, our problem is:
>> >>> - there are two separate USB PHYs on Meson GXBB
>> >>> - both are sharing the same reset line (provided by the reset-meson driver)
>> >>> - during initialization of the PHYs we must only call
>> >>> reset_control_reset(rstc) once (if we do it for the first *and* second
>> >>> PHY then the first PHY gets confused once the second PHY uses the
>> >>> reset because the first PHY's state is reset as well)
>> >>
>> >> If you have an initially asserted reset line and you can enable the
>> >> first module by deasserting the reset via reset_control_deassert (and
>> >> reset_control_assert to signal when the module may be disabled again
>> >> after use), shared resets are for you.
>> >>
>> >> If you need a reset pulse or have no direct control over the reset line,
>> >> (device_reset), the reset framework currently has no solution for this.
>> >> The ugly thing about reset_control_once would be that it can't re-reset
>> >> modules when unloading and reloading driver modules.
>> >
>> > The corresponding reset driver in question is reset-meson, which only
>> > implements reset (assert/deassert are not implemented). However, I
>> > don't know if this is due to hardware design.
>> > I think the hardware implements the latter, but maybe Neil can give
>> > more information here (I currently don't have access to my board so I
>> > cannot test how the hardware actually behaves).
>>
>> It's implemented that way because the hardware only supports a reset
>> pulse.
>
> Would it be possible to bring down both PHYs drivers, pull the reset
> line once, and then bring the drivers back up again?
I guess that this is the rmmod case: I haven't tested it yet but that
should work (even with the current code and .dts)