linux-kernel - Re: [PATCH 2/2] net: mv643xx_eth: proper initialization for Kirkwood SoCs

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Date:	Tue, 28 May 2013 14:02:27 -0400
From:	Jason Cooper <jason@...edaemon.net>
To:	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
Cc:	Andrew Lunn <andrew@...n.ch>,
	Benjamin Herrenschmidt <benh@...nel.crashing.org>,
	linux-kernel@...r.kernel.org,
	Lennert Buytenhek <buytenh@...tstofly.org>,
	netdev@...r.kernel.org, linuxppc-dev@...ts.ozlabs.org,
	David Miller <davem@...emloft.net>,
	linux-arm-kernel@...ts.infradead.org,
	Sebastian Hesselbarth <sebastian.hesselbarth@...il.com>
Subject: Re: [PATCH 2/2] net: mv643xx_eth: proper initialization for
 Kirkwood SoCs

Jason,

Sorry, I meant to get back to this earlier and it slipped off of my
plate. :(

On Fri, May 24, 2013 at 11:33:06AM -0600, Jason Gunthorpe wrote:
> On Fri, May 24, 2013 at 12:46:36PM -0400, Jason Cooper wrote:
> 
> > > Why are you not keen on this? It seems like normal device driver
> > > practice, that is what the data field of of_device_id is typically
> > > used for..
> > 
> > I'm not keen on it because we don't have a document saying "All kirkwood
> > SoCs need PSC1 set to X after reset."  We know it, but have we tested
> > the 6282?
> 
> I disagree. The manul is very clear how PSC1 must be set for proper
> operation. Clk125BypassEn bit is used only for loopback testing, it
> should never set for driver operation. Similarly PortReset must be
> cleared for driver operation.
> 
> It is always safe for the driver to clear these bits, if it knows they
> are available.  In fact, I would argue the driver should always clear
> these bits so that the bootloader isn't relied on to do it. It doesn't
> matter if the SOC errantly sets the bit or not, it can *always* be
> safely cleared.

Great!

> Further, I compared my 88F6282/88F6283 manual against the public
> 88F6180/88F619x/88F6281 spec and confirmed that the PSC1 layout is the
> same.

Even better.

> So all of these SOC's can share a driver compatible string.

Ok, "marvell,kirkwood-eth" works for me then.  I think Sebastian already
has patches for that.

> AFAICT the only reason the driver doesn't touch PSC1 today is because
> the PSC1 was introduced in a later IP revision and its presence isn't
> auto-detectable.

Makes sense.

> The last bit of the puzzle to get bootloader independence on kirkwood
> is to encode the phy interface type (GMII/RGMII/BASE-X) in the DT so
> the entire PSC1 can be set by the driver..

Hmm, let's work on that separately, and later.  I've snowballed this
attempt enough ;-)

Thanks for digging into this for us,

Jason.
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