linux-kernel - Re: [PATCH v6 12/17] phy: sun4i-usb: Introduce port2 SIDDQ quirk

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Date:   Mon, 7 Jun 2021 15:17:42 +0100
From:   Andre Przywara <andre.przywara@....com>
To:     Maxime Ripard <maxime@...no.tech>
Cc:     Chen-Yu Tsai <wens@...e.org>,
        Jernej Skrabec <jernej.skrabec@...il.com>,
        Rob Herring <robh@...nel.org>, Icenowy Zheng <icenowy@...c.io>,
        Samuel Holland <samuel@...lland.org>,
        Ondrej Jirman <megous@...ous.com>,
        linux-arm-kernel@...ts.infradead.org, linux-sunxi@...glegroups.com,
        linux-sunxi@...ts.linux.dev, linux-kernel@...r.kernel.org,
        Kishon Vijay Abraham I <kishon@...com>,
        Vinod Koul <vkoul@...nel.org>, linux-phy@...ts.infradead.org,
        linux-usb@...r.kernel.org
Subject: Re: [PATCH v6 12/17] phy: sun4i-usb: Introduce port2 SIDDQ quirk

On Mon, 7 Jun 2021 15:22:55 +0200
Maxime Ripard <maxime@...no.tech> wrote:

Hi Maxime,

> On Tue, May 25, 2021 at 12:29:01PM +0100, Andre Przywara wrote:
> > On Mon, 24 May 2021 13:59:46 +0200
> > Maxime Ripard <maxime@...no.tech> wrote:
> > 
> > Hi Maxime,
> >   
> > > On Wed, May 19, 2021 at 11:41:47AM +0100, Andre Przywara wrote:  
> > > > At least the Allwinner H616 SoC requires a weird quirk to make most
> > > > USB PHYs work: Only port2 works out of the box, but all other ports
> > > > need some help from this port2 to work correctly: The CLK_BUS_PHY2 and
> > > > RST_USB_PHY2 clock and reset need to be enabled, and the SIDDQ bit in
> > > > the PMU PHY control register needs to be cleared. For this register to
> > > > be accessible, CLK_BUS_ECHI2 needs to be ungated. Don't ask ....
> > > > 
> > > > Instead of disguising this as some generic feature, do exactly that
> > > > in our PHY init:
> > > > If the quirk bit is set, and we initialise a PHY other than PHY2, ungate
> > > > this one special clock, and clear the SIDDQ bit. We can pull in the
> > > > other required clocks via the DT.
> > > > 
> > > > Signed-off-by: Andre Przywara <andre.przywara@....com>    
> > > 
> > > What is this SIDDQ bit doing exactly?  
> > 
> > I probably know as much as you do, but as Jernej pointed out, in some
> > Rockchip code it's indeed documented as some analogue PHY supply switch:
> > ($ git grep -i siddq drivers/phy/rockchip)
> > 
> > In fact we had this pin/bit for ages, it was just hidden as BIT(1) in
> > our infamous PMU_UNK1 register. Patch 10/17 drags that into the light.  
> 
> Ok
> 
> > > I guess we could also expose this using a power-domain if it's relevant?  
> > 
> > Mmmh, interesting idea. So are you thinking about registering a genpd
> > provider in sun4i_usb_phy_probe(), then having a power-domains property
> > in the ehci/ohci nodes, pointing to the PHY node? And if yes, should
> > the provider be a subnode of the USB PHY node, with a separate
> > compatible? That sounds a bit more involved, but would have the
> > advantage of allowing us to specify the resets and clocks from PHY2
> > there, and would look a bit cleaner than hacking them into the
> > other EHCI/OHCI nodes.  
> 
> I'm not sure we need a separate device node, we could just register the
> phy driver as a genpd provider, and then with an arg (so with
> of_genpd_add_provider_onecell?) the index of the USB controller we want
> to power up.

Yeah, I figured that myself meanwhile ;-) I now have a fairly nice
implementation, which does away with the extra clocks and resets from
the EHCI/OHCI nodes, and just adds one extra clock to the PHY node. The
rest is power domains properties.

> > I would not touch the existing SoCs (even though it seems to apply to
> > them as well, just not in the exact same way), but I can give it a
> > try for the H616. It seems like the other SIDDQ bits (in the other
> > PHYs) are still needed for operation, but the PD provide could actually
> > take care of this as well.
> > 
> > Does that make sense or is this a bit over the top for just clearing an
> > extra bit?  
> 
> Using what I described above should be fairly simple, so if we can fit
> in an available and relevant abstraction, yeah, I guess :)

Thanks!
I will post what I have, just need to find some solution for the RTC
clock bits.

Cheers,
Andre