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

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Message-ID: <ce3426b50a2593c23052b83848e95db8e49fdb8a.camel@pengutronix.de>
Date: Tue, 25 Mar 2025 16:13:00 +0100
From: Philipp Zabel <p.zabel@...gutronix.de>
To: Fabrizio Castro <fabrizio.castro.jz@...esas.com>, 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 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.

> 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.

regards
Philipp