netdev - Re: [PATCH v2 7/8] net: mvmdio: add xmdio support

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Message-ID: <20170609200047.GV4902@n2100.armlinux.org.uk>
Date:   Fri, 9 Jun 2017 21:00:48 +0100
From:   Russell King - ARM Linux <linux@...linux.org.uk>
To:     Antoine Tenart <antoine.tenart@...e-electrons.com>
Cc:     Andrew Lunn <andrew@...n.ch>, davem@...emloft.net,
        jason@...edaemon.net, gregory.clement@...e-electrons.com,
        sebastian.hesselbarth@...il.com, f.fainelli@...il.com,
        thomas.petazzoni@...e-electrons.com, mw@...ihalf.com,
        netdev@...r.kernel.org, linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2 7/8] net: mvmdio: add xmdio support

On Fri, Jun 09, 2017 at 08:40:19AM +0200, Antoine Tenart wrote:
> Hi Andrew,
> 
> On Thu, Jun 08, 2017 at 06:03:31PM +0200, Andrew Lunn wrote:
> > On Thu, Jun 08, 2017 at 11:26:52AM +0200, Antoine Tenart wrote:
> > > +#define MVMDIO_XSMI_MGNT_REG		0x0
> > > +#define  MVMDIO_XSMI_READ_VALID		BIT(29)
> > > +#define  MVMDIO_XSMI_BUSY		BIT(30)
> > > +#define MVMDIO_XSMI_ADDR_REG		0x8
> > > +#define  MVMDIO_XSMI_PHYADDR_SHIFT	16
> > > +#define  MVMDIO_XSMI_DEVADDR_SHIFT	21
> > > +#define  MVMDIO_XSMI_READ_OPERATION	(0x7 << 26)
> > > +#define  MVMDIO_XSMI_WRITE_OPERATION	(0x5 << 27)
> > 
> > These two operations seem odd. Generally ops have the same shift.
> 
> Indeed, this is odd. I'll have a look at this.

The Marvell driver uses 5 << 26:

+#define XOPCODE_OFFS           26
+#define XOPCODE_ADDR_READ      (7 << XOPCODE_OFFS)
+#define XOPCODE_ADDR_WRITE     (5 << XOPCODE_OFFS)

What this means is that with the incorrect shift in your driver,
although writes appeared to work, they actually resulted in a
post-read-increment-address frame (and hence no error.)

-- 
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