linux-kernel - Re: [PATCH v5 1/6] drivers: phy: add generic PHY framework

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Message-ID: <20130403142747.GK14680@arwen.pp.htv.fi>
Date:	Wed, 3 Apr 2013 17:27:47 +0300
From:	Felipe Balbi <balbi@...com>
To:	Kishon Vijay Abraham I <kishon@...com>
CC:	<balbi@...com>, <gregkh@...uxfoundation.org>, <arnd@...db.de>,
	<akpm@...ux-foundation.org>, <swarren@...dotorg.org>,
	<sylvester.nawrocki@...il.com>, <rob@...dley.net>,
	<netdev@...r.kernel.org>, <davem@...emloft.net>,
	<cesarb@...arb.net>, <linux-usb@...r.kernel.org>,
	<linux-omap@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
	<tony@...mide.com>, <grant.likely@...retlab.ca>,
	<rob.herring@...xeda.com>, <b-cousson@...com>,
	<linux@....linux.org.uk>, <eballetbo@...il.com>,
	<javier@...hile0.org>, <mchehab@...hat.com>,
	<santosh.shilimkar@...com>, <broonie@...nsource.wolfsonmicro.com>,
	<swarren@...dia.com>, <linux-doc@...r.kernel.org>,
	<devicetree-discuss@...ts.ozlabs.org>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v5 1/6] drivers: phy: add generic PHY framework

hi,

On Wed, Apr 03, 2013 at 07:48:42PM +0530, Kishon Vijay Abraham I wrote:
> >>+struct phy *of_phy_xlate(struct phy *phy, struct of_phandle_args *args)
> >>+{
> >>+	return phy;
> >>+}
> >>+EXPORT_SYMBOL_GPL(of_phy_xlate);
> >
> >so you get a PHY and just return it ? What gives ?? (maybe I skipped
> >some of the discussion...)
> 
> hmm.. this is for the common case where the PHY provider implements
> only one PHY. And both phy provider and phy_instance is represented
> by struct phy *.
> 
> For the case where PHY provider implements multiple PHYs (here it
> will have a single dt node), the PHY provider will implement it's own
> version of of_xlate that takes *of_phandle_args* as argument and
> finds the appropriate PHY.

got it.

> >>+struct phy *of_phy_get(struct device *dev, int index)
> >>+{
> >>+	int ret;
> >>+	struct phy *phy = NULL;
> >>+	struct phy_bind *phy_map = NULL;
> >>+	struct of_phandle_args args;
> >>+	struct device_node *node;
> >>+
> >>+	if (!dev->of_node) {
> >>+		dev_dbg(dev, "device does not have a device node entry\n");
> >>+		return ERR_PTR(-EINVAL);
> >>+	}
> >>+
> >>+	ret = of_parse_phandle_with_args(dev->of_node, "phys", "#phy-cells",
> >>+		index, &args);
> >>+	if (ret) {
> >>+		dev_dbg(dev, "failed to get phy in %s node\n",
> >>+			dev->of_node->full_name);
> >>+		return ERR_PTR(-ENODEV);
> >>+	}
> >>+
> >>+	phy = of_phy_lookup(args.np);
> >>+	if (IS_ERR(phy) || !try_module_get(phy->ops->owner)) {
> >>+		phy = ERR_PTR(-EPROBE_DEFER);
> >>+		goto err0;
> >>+	}
> >>+
> >>+	phy = phy->ops->of_xlate(phy, &args);
> >
> >alright, so of_xlate() is optional, am I right ? How about not
> 
> Not really. of_xlate is mandatory (it's even checked in phy_create).
> Either the PHY provider can implement it's own version or use the
> implementation above (by filling the function pointer).

alright.

> >implementing the above and have a check for of_xlate() being a valid
> >pointer here ?
> 
> Having the way it is actually mandates the PHY providers to always
> provide of_xlate which IMO is better since some PHY providers wont
> accidentally be using the default implementation.

ok cool, thanks for clarifying.

> >>+		ret = -EINVAL;
> >>+		goto err0;
> >>+	}
> >>+
> >>+	if (!phy_class)
> >>+		phy_core_init();
> >
> >why don't you setup the class on module_init ? Then this would be a
> >terrible error condition here :-)
> 
> This is for the case where the PHY driver gets loaded before the PHY
> framework. I could have returned EPROBE_DEFER here instead I thought
> will have it this way.

looks a bit weird IMO. Is it really possible for PHY to load before ?
Since PHY driver uses symbols from phy-core, modprobe will make sure to
load drivers based on symbol dependency, right ?

> >>+static struct device_attribute phy_dev_attrs[] = {
> >>+	__ATTR(label, 0444, phy_name_show, NULL),
> >>+	__ATTR(phy_bind, 0444, phy_bind_show, NULL),
> >
> >you could expose a human-readable 'type' string. BTW, how are you using
> >type ? USB2/USB3/etc ? Have you considered our OMAP5 SerDes pair which
> 
> Actually not using *type* anywhere. Just used as an additional info
> about the PHY. It's actually not even enum. Maybe I can remove it
> completely.

makes sense.

> >are currently for USB3 and SATA (and could just as easily be used for
> >PCIe)
> 
> Yeah. Me and Balaji were planning to work on it for having a single
> driver to be used for all the above.

cool :-)

-- 
balbi

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