linux-kernel - RE: [PATCH 00/16] Add initial USB support for the Renesas RZ/G3S SoC

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Message-ID:
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Date: Mon, 2 Sep 2024 10:47:50 +0000
From: Biju Das <biju.das.jz@...renesas.com>
To: Claudiu.Beznea <claudiu.beznea@...on.dev>, Ulf Hansson
	<ulf.hansson@...aro.org>
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 Shimoda <yoshihiro.shimoda.uh@...esas.com>, "linux-phy@...ts.infradead.org"
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	<linux-clk@...r.kernel.org>, "linux-pm@...r.kernel.org"
	<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: 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.

Cheers,
Biju