linux-kernel - RE: [PATCH v2 2/2] reset: Add USB2PHY control driver for Renesas RZ/V2H(P)

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Message-ID:
 <TYCPR01MB120937131DE070FC67C96825FC2A72@TYCPR01MB12093.jpnprd01.prod.outlook.com>
Date: Tue, 25 Mar 2025 15:43:39 +0000
From: Fabrizio Castro <fabrizio.castro.jz@...esas.com>
To: Philipp Zabel <p.zabel@...gutronix.de>, Prabhakar
	<prabhakar.csengg@...il.com>, Geert Uytterhoeven <geert+renesas@...der.be>,
	Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>, Magnus Damm <magnus.damm@...il.com>
CC: "devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-renesas-soc@...r.kernel.org" <linux-renesas-soc@...r.kernel.org>, Biju
 Das <biju.das.jz@...renesas.com>, Prabhakar Mahadev Lad
	<prabhakar.mahadev-lad.rj@...renesas.com>, Chris Paterson
	<Chris.Paterson2@...esas.com>
Subject: RE: [PATCH v2 2/2] reset: Add USB2PHY control driver for Renesas
 RZ/V2H(P)

Hi Philipp,

Thanks for your feedback!

> From: Philipp Zabel <p.zabel@...gutronix.de>
> Sent: 25 March 2025 15:13
> Subject: Re: [PATCH v2 2/2] reset: Add USB2PHY control driver for Renesas RZ/V2H(P)
> 
> Hi Fabrizio, Prabhakar,
> 
> On Di, 2025-03-18 at 12:31 +0000, Fabrizio Castro wrote:
> > Hi Philipp,
> >
> > Thanks for your feedback!
> >
> > > From: Philipp Zabel <p.zabel@...gutronix.de>
> > > Sent: 13 March 2025 13:06
> > > Subject: Re: [PATCH v2 2/2] reset: Add USB2PHY control driver for Renesas RZ/V2H(P)
> > >
> > > Hi Fabrizio,
> > >
> > > On Do, 2025-03-13 at 10:14 +0000, Fabrizio Castro wrote:
> > > > Hi Philipp,
> > > >
> > > > Thanks for your feedback!
> > > >
> > > > > From: Philipp Zabel <p.zabel@...gutronix.de>
> > > > > Sent: 13 March 2025 08:37
> > > > > Subject: Re: [PATCH v2 2/2] reset: Add USB2PHY control driver for Renesas RZ/V2H(P)
> > > > >
> > > > > On Mi, 2025-03-05 at 12:39 +0000, Prabhakar wrote:
> > > > > > From: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > > > >
> > > > > > Add support for the USB2PHY control driver on the Renesas RZ/V2H(P) SoC.
> > > > > > Make the driver handle reset and power-down operations for the USB2PHY.
> > > > > >
> > > > > > Pass OF data to support future SoCs with similar USB2PHY hardware but
> > > > > > different register configurations. Define device-specific initialization
> > > > > > values and control register settings in OF data to ensure flexibility
> > > > > > for upcoming SoCs.
> > > > > >
> > > > > > Signed-off-by: Lad Prabhakar <prabhakar.mahadev-lad.rj@...renesas.com>
> > > > > > ---
> > > > > >  drivers/reset/Kconfig                    |   7 +
> > > > > >  drivers/reset/Makefile                   |   1 +
> > > > > >  drivers/reset/reset-rzv2h-usb2phy-ctrl.c | 223 +++++++++++++++++++++++
> > > > > >  3 files changed, 231 insertions(+)
> > > > > >  create mode 100644 drivers/reset/reset-rzv2h-usb2phy-ctrl.c
> > > > > >
> > > [...]
> > > > > > diff --git a/drivers/reset/reset-rzv2h-usb2phy-ctrl.c b/drivers/reset/reset-rzv2h-usb2phy-
> ctrl.c
> > > > > > new file mode 100644
> > > > > > index 000000000000..a6daeaf37e1c
> > > > > > --- /dev/null
> > > > > > +++ b/drivers/reset/reset-rzv2h-usb2phy-ctrl.c
> > > > > > @@ -0,0 +1,223 @@
> > > [...]
> > > > > > +static const struct rzv2h_usb2phy_regval rzv2h_init_vals[] = {
> > > > > > +	{ .reg = 0xc10, .val = 0x67c },
> > > > > > +	{ .reg = 0xc14, .val = 0x1f },
> > > > > > +	{ .reg = 0x600, .val = 0x909 },
> > > > >
> > > > > What are these registers and what are those values doing?
> > > >
> > > > Unfortunately, there are some licensing restrictions on this IP, this is
> > > > the best that we can do, as per the license agreement.
> > >
> > > How am I expected to review this?
> > >
> > > For now, I'll assume that these registers are not related to reset
> > > functionality at all, and that this driver should be a phy controller
> > > driver instead of a reset controller driver.
> > >
> > > Can you convince me otherwise without breaking license agreements?
> >
> > Sorry about the delay, as you may have figured out, we had to double check with
> > the LSI team before making any statement.
> >
> > We can confirm that `rzv2h_init_vals` contains the registers and corresponding
> > initialization values required to prepare the PHY to receive assert and deassert
> > requests. This is a one time only thing, done at probe.
> 
> Thank you. Please document this in a comment next to the
> rzv2h_init_vals[] table.

Will do, thank you.

> 
> > After looking into things again, I have noticed that the probe function is missing
> > calling into the assert sequence, and the status of the reset is undefined, so
> > that's something to fix for v3 to make it initialize in asserted state.
> >
> > The assert, deassert, and status operations are only touching reset related registers.
> > Nothing else.
> >
> > Therefore we believe this should be a port reset driver.
> >
> > Thanks for your patience so far, and sorry for being cryptic.
> 
> Let's go ahead with this driver. I'd be happy about a MAINTAINERS entry
> for it.

Thank you! And we'll definitely add a MAINTAINERS entry for this.

Cheers,
Fab

> 
> regards
> Philipp