[PATCH 00/16] Add initial USB support for the Renesas RZ/G3S SoC

[Biju Das]

Hi Claudiu,

> -----Original Message-----
> From: claudiu beznea <claudiu.beznea at tuxon.dev>
> Sent: Tuesday, September 3, 2024 11:25 AM
> Subject: Re: [PATCH 00/16] Add initial USB support for the Renesas RZ/G3S SoC
> 
> 
> 
> On 03.09.2024 10:18, Biju Das wrote:
> > Hi Claudiu,
> >
> >> -----Original Message-----
> >> From: Biju Das
> >> Sent: Monday, September 2, 2024 11:48 AM
> >> Subject: RE: [PATCH 00/16] Add initial USB support for the Renesas
> >> RZ/G3S SoC
> >>
> >> Hi Claudiu,
> >>
> >>> -----Original Message-----
> >>> From: claudiu beznea <claudiu.beznea at tuxon.dev>
> >>> Sent: Monday, September 2, 2024 11:41 AM
> >>> Subject: Re: [PATCH 00/16] Add initial USB support for the Renesas
> >>> RZ/G3S SoC
> >>>
> >>>
> >>>
> >>> On 02.09.2024 12:18, Biju Das wrote:
> >>>>>>>> Do you have any plan to control this power transitions(ALL_ON to AWO and vice versa) in
> linux?
> >>>>>>> As you know, the RZ/G3S USB PM code is already prepared. This is
> >>>>>>> also configuring these signals when going to suspend/exiting from resume.
> >>>>>>> W/o configuring properly these signals the USB is not working after a suspend/resume cycle.
> >>>>>> One option is to handle SYSC USB PWRRDY signal in TF-A, if you
> >>>>>> plan to handle system transitions
> >>>>> there??
> >>>>>
> >>>>> As I mentioned, the settings in these registers may be changed by
> >>>>> intermediary booting
> >>> applications.
> >>>>> Depending on that, Linux need to control it also on probe for USB
> >>>>> to work (it should be the same with PCIe, these signals seems
> >>>>> similar from HW manual
> >> description).
> >>>> You mean system transition settings will be override by U-boot, so
> >>>> Linux needs to restore it
> >> back??
> >>>
> >>> It was talking about booting...
> >>
> >> I am also referring to boot. Boot starts with TF-A and it has a system state.
> >>
> >>>
> >>> You proposed to handle SYSC signals from TF-A in a discussion about system power transitions:
> >>>
> >>> "One option is to handle SYSC USB PWRRDY signal in TF-A,  if you plan to handle system
> transitions"
> >>>
> >>> (I was guessing the "system transition" statement there refers to
> >>> power states transitions, ALL_ON <->
> >>> AWO/VBAT)
> >>
> >> That is correct.
> >>
> >>>
> >>> and I gave the booting process as a counter example: if we handle it
> >>> in TF-A it may not be enough as these signals might be changed by
> >>> intermediary booting applications
> >> (e.g., U-Boot).
> >>
> >> Why should U-boot override, system state signals such as USB PWRREADY? Can you please give an
> example.
> >>
> >>>
> >>> To conclude, there are 3 scenarios I see where these signals need to
> >>> be
> >>> handled:
> >>> 1/ booting
> >>> 2/ suspend to RAM
> >>> 3/ driver unbind/bind
> >>
> >> --> It should be OK as linux is not handling USB PWRREADY signal.
> >>
> >>>
> >>> In case of booting: if we have TF-A to set signals there might be
> >>> intermediary booting applications (e.g. U-Boot) that set these
> >>> signals also. If it leaves it in improper state and Linux wants to
> >>> use USB then the USB will not work (if
> >> Linux doesn't handle it).
> >>
> >> That is the problem of U-boot. U-boot should not override system state signals such as USB
> PWRREADY.
> >>
> >>>
> >>> In case of suspend to RAM: as TF-A is the only application in the
> >>> suspend to RAM chain, it should work handling it in TF-A.
> >>
> >> That is correct, TF-A should handle based on system state.
> >>
> >>>
> >>> In case of unbind/bind: currently we don't know if these signals
> >>> introduces any kind of power saving so asserting/de-asserting them
> >>> in Linux may be useful from this
> >> perspective, if any.
> >>
> >> These are system signals, according to me should not be used in unbind/bind.
> >>
> >> I may be wrong.
> >
> > Just to add the below are the 4 system states (power mode) for this LSI.
> >
> > If I understand correctly, we need to configure USB PWRRDY signal only
> > when there is a transition from ALL_ON to AWO mode and vice versa.
> > as you see on AWO mode only CM-33 is active.
> >
> > • ALL_OFF mode: All CPUs and peripheral modules can not be worked.
> > • ALL_ON mode: All CPUs and peripheral modules can be worked.
> > • AWO mode: Cortex-M33 and peripheral modules in PD_VCC and PD_VBATT domain can be worked.
> > • VBATT mode: Only RTC, tamper detection and backup registers can be worked.
> >
> > System manager which is controlling both CA-55 and CM-33, will set USB
> > PWRRDY signal based on system state.
> >
> > Since we don't have system manager for controlling both CA-55 and
> > CM-33 Probably from CA-55 perspective, TF-A should be sufficient.
> >
> > During boot clr USB PWR READY signal in TF-A.
> > STR case, suspend set USB PWR READY signal in TF-A.
> > STR case, resume clr USB PWR READY signal in TF-A.
> 
> As I said previously, it can be done in different ways. My point was to let Linux set what it needs
> for all it's devices to work. I think the way to go forward is a maintainer decision.


I agree, there can be n number of solution for a problem.

Since you modelled system state signal (USB PWRRDY) as reset control signal, it is reset/DT maintainer's decision
to say the final word whether this signal fits in reset system framework or not?

Cheers,
biju