linux-kernel - Re: [PATCH v1 4/9] pinctrl: tegra-xusb: Add USB PHY support

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Message-ID: <20140627150004.GF8069@saruman.home>
Date:	Fri, 27 Jun 2014 10:00:04 -0500
From:	Felipe Balbi <balbi@...com>
To:	Andrew Bresticker <abrestic@...omium.org>
CC:	Stephen Warren <swarren@...dotorg.org>,
	<devicetree@...r.kernel.org>, <linux-doc@...r.kernel.org>,
	"linux-tegra@...r.kernel.org" <linux-tegra@...r.kernel.org>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>,
	<linux-usb@...r.kernel.org>, Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	Kumar Gala <galak@...eaurora.org>,
	Randy Dunlap <rdunlap@...radead.org>,
	Thierry Reding <thierry.reding@...il.com>,
	Russell King <linux@....linux.org.uk>,
	Linus Walleij <linus.walleij@...aro.org>,
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
	Mathias Nyman <mathias.nyman@...el.com>,
	Grant Likely <grant.likely@...aro.org>,
	Alan Stern <stern@...land.harvard.edu>,
	Kishon Vijay Abraham I <kishon@...com>,
	Arnd Bergmann <arnd@...db.de>, <balbi@...com>
Subject: Re: [PATCH v1 4/9] pinctrl: tegra-xusb: Add USB PHY support

On Wed, Jun 25, 2014 at 04:30:48PM -0700, Andrew Bresticker wrote:
> >> +static int usb3_phy_power_on(struct phy *phy)
> >> +{
> >> +     struct tegra_xusb_padctl *padctl = phy_get_drvdata(phy);
> >> +     int port = usb3_phy_to_port(phy);
> >> +     int lane = padctl->usb3_ports[port].lane;
> >> +     u32 value, offset;
> >> +
> >> +     value = padctl_readl(padctl, XUSB_PADCTL_IOPHY_USB3_PADX_CTL2(port));
> >> +     value &= ~((XUSB_PADCTL_IOPHY_USB3_PAD_CTL2_RX_WANDER_MASK <<
> >> +                 XUSB_PADCTL_IOPHY_USB3_PAD_CTL2_RX_WANDER_SHIFT) |
> >> +                (XUSB_PADCTL_IOPHY_USB3_PAD_CTL2_RX_EQ_MASK <<
> >> +                 XUSB_PADCTL_IOPHY_USB3_PAD_CTL2_RX_EQ_SHIFT) |
> >> +                (XUSB_PADCTL_IOPHY_USB3_PAD_CTL2_CDR_CNTL_MASK <<
> >> +                 XUSB_PADCTL_IOPHY_USB3_PAD_CTL2_CDR_CNTL_SHIFT));
> >
> > Hmm. So there is a lot of "PHY" stuff here after all.
> >
> > However, the PHYs implemented here appear to implement very low-level
> > I/O pad code, whereas the PHYs we have for our USB 2.0 controller are
> > somewhat higher-level; they're more USB-oriented than just IO pad
> > oriented. Do you know which level of abstraction a Linux PHY object is
> > supposed to be? I could never get an answer when I asked before.
> 
> The only other PHY driver I've worked with (Exynos USB2/3 PHYs) also
> mainly only did low-level pad control stuff, but looking at a couple
> of other USB PHYs (MSM, MV), there appear to be others that have
> higher-level USB stuff in the PHY driver.  Perhaps Kishon or Felipe
> could offer us some guidance?

well, if you're adding a new driver, I'd rather see folks moving over to
the generic phy framework (drivers/phy) because we're trying really hard
to get rid of drivers/usb/phy/. And I think, in your case, it's actually
ok to use pinctrl because you actually are muxing pads to the USB3 PHY,
you just do it lazyly.

my 2 cents

-- 
balbi

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