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Date: Sat, 31 Aug 2024 05:13:38 +0000
From: Biju Das <biju.das.jz@...renesas.com>
To: Claudiu.Beznea <claudiu.beznea@...on.dev>, Ulf Hansson
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	<linux-pm@...r.kernel.org>, Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
Subject: RE: [PATCH 00/16] Add initial USB support for the Renesas RZ/G3S SoC

Hi Claudiu,

> -----Original Message-----
> From: claudiu beznea <claudiu.beznea@...on.dev>
> Sent: Friday, August 30, 2024 9:23 AM
> Subject: Re: [PATCH 00/16] Add initial USB support for the Renesas RZ/G3S SoC
> 
> Hi, Ulf,
> 
> On 29.08.2024 18:26, Ulf Hansson wrote:
> > On Thu, 22 Aug 2024 at 17:28, Claudiu <claudiu.beznea@...on.dev> wrote:
> >>
> >> From: Claudiu Beznea <claudiu.beznea.uj@...renesas.com>
> >>
> >> Hi,
> >>
> >> Series adds initial USB support for the Renesas RZ/G3S SoC.
> >>
> >> Series is split as follows:
> >>
> >> - patch 01/16           - add clock reset and power domain support for USB
> >> - patch 02-04/16        - add reset control support for a USB signal
> >>                           that need to be controlled before/after
> >>                           the power to USB area is turned on/off.
> >>
> >>                           Philipp, Ulf, Geert, all,
> >>
> >>                           I detailed my approach for this in patch
> >>                           04/16, please have a look and let me know
> >>                           your input.
> >
> > I have looked briefly. Your suggested approach may work, but I have a
> > few thoughts, see below.
> >
> > If I understand correctly, it is the consumer driver for the device
> > that is attached to the USB power domain that becomes responsible for
> > asserting/de-asserting this new signal. Right?
> 
> Right!
> 
> >
> > In this regard, please note that the consumer driver doesn't really
> > know when the power domain really gets powered-on/off. Calling
> > pm_runtime_get|put*() is dealing with the reference counting. For
> > example, a call to pm_runtime_get*() just makes sure that the PM
> > domain gets-or-remains powered-on. Could this be a problem from the
> > reset-signal point of view?
> 
> It should be safe. From the HW manual I understand the hardware block is something like the following:
> 
> 
>                   USB area
>          +-------------------------+
>          |                         |
>          | PHY --->USB controller  |
> SYSC --> |  ^                      |
>          |  |                      |
>          | PHY reset               |
>          +-------------------------+

How USB PWRRDY signal is connected to USB? 

USB block consists of PHY control, PHY, USB HOST and USB OTG Controller IPs.

Is it connected to top level block or connected to each IP's for turning off the USB region power?

? Or Just PHY (HW manual mentions for AWO, the USB PWRRDY signal->USB PHY PWRRDY signal control)? 

If the USBPWRRDY signal is connected across modules with this reset signal approach
then you may need to update bindings [1] with that reset signal

[1] https://patchwork.kernel.org/project/linux-renesas-soc/patch/20240822152801.602318-12-claudiu.beznea.uj@bp.renesas.com/
 

Cheers,
Biju

> 
> Where:
> - SYSC is the system controller that controls the new signal for which
>   I'm requesting opinions in this series
> - PHY reset: is the block controlling the PHYs
> - PHY: is the block controlling the USB PHYs
> - USB controller: is the USB controller
> 
> Currently, I passed the SYSC signal handling to the PHY reset driver; w/o PHY reset the rest of the
> USB logic cannot work (neither PHY block nor USB controller).
> 
> Currently, the PHY reset driver call pm_runtime_resume_and_get() in probe and pm_runtime_put() in
> remove. The struct reset_control_ops::{assert, deassert} only set specific bits in registers (no
> pm_runtime* calls).
> 
> The PHY driver is taking its PHY reset in probe and release it in remove().
> With this approach the newly introduced SYSC signal will be de-asserted/asserted only in the PHY reset
> probe/remove (either if it is handled though PM domain or reset control signal).
> 
> If the SYSC signal would be passed to all the blocks in the USB area (and it would be handled though
> PM domains) it should be no problem either, AFAICT, because of reference counting the
> pm_runtime_get|put*() is taking care of. As the PHY reset is the root node the in the devices node
> tree for USB the reference counting should work, too (I may miss something though, please correct me
> if I'm wrong).
> 
> If the SYSC signal would be handled though a reset control driver (as proposed in this series) and we
> want to pass this reference to all the blocks in the USB area then we can request the reset signal as
> shared and, AFAIK, this is also reference counted. The devices node tree should help with the order,
> too, if I'm not wrong.
> 
> Thank you for looking at this,
> Claudiu Beznea
> 
> >
> > [...]
> >
> > Kind regards
> > Uffe

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