netdev - Re: [PATCH v8 2/3] net: hisilicon: new hip04 MDIO driver

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Message-Id: <201404221630.07865.arnd@arndb.de>
Date:	Tue, 22 Apr 2014 16:30:07 +0200
From:	Arnd Bergmann <arnd@...db.de>
To:	zhangfei <zhangfei.gao@...aro.org>
Cc:	linux-arm-kernel@...ts.infradead.org,
	Sergei Shtylyov <sergei.shtylyov@...entembedded.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	Eric Dumazet <eric.dumazet@...il.com>,
	netdev <netdev@...r.kernel.org>, xuwei5@...ilicon.com,
	David Laight <David.Laight@...lab.com>,
	David Miller <davem@...emloft.net>
Subject: Re: [PATCH v8 2/3] net: hisilicon: new hip04 MDIO driver

On Tuesday 22 April 2014, zhangfei wrote:
> On 04/22/2014 04:22 PM, Arnd Bergmann wrote:
> 
> >> It's private register of the phy marvell 88e1512.
> >> To make it clearer using define instead.
> >> #define MII_MARVELL_PHY_PAGE    22
> >>
> >> The registers has been grouped into several pages, access register need
> >> choose which page first.
> >
> > You shouldn't touch the PHY private registers in the main driver though,
> > this should be purely handled by drivers/net/phy/marvell.c.
> >
> > I don't see support for 88e1512 there, only 88e1510 and lots of older
> > ones, but I assume it isn't hard to add.
> >
> 
> 88e1512 driver is already supported, same as 88e1510.
> #define MARVELL_PHY_ID_MASK             0xfffffff0
> So it should support 88e151x.
> 
> Reset is required here for get_phy_id, otherwise only 0 can be get.
> phy_device_create will not be called, and can not match any driver.
> 
> However in the experiment, it is found BMCR_RESET is not required in fact.
> Only hip04_mdio_write(bus, i, MII_MARVELL_PHY_PAGE, 0) has to be set.
> 88e151x registers are divided into pages.
> Generic MII registers is in page 0, including MII_PHYSID1 and MII_PHYSID2.
> Unfortunately the default page is not 0, so get_phy_id will fail.
> 
> So bus->reset still required to set the page to 0, prepared for get_phy_id.

But it means that the hip04_mdio driver potentially won't work if connected
to something other than a Marvell PHY.

I noticed that the marvell_of_reg_init() does this at init time:

saved_page = phy_read(phydev, MII_MARVELL_PHY_PAGE);
... /* perform init */
if (page_changed)
	phy_write(phydev, MII_MARVELL_PHY_PAGE, saved_page);

Is this a bug? Maybe it should always set page 0 when leaving
this function.

	Arnd
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