linux-kernel - Re: [PATCH 04/10] net: stmmac: sunxi platfrom extensions for GMAC in Allwinner A20 SoC's

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Message-ID: <1455361.VIrFSPex2v@flatron>
Date:	Sat, 07 Dec 2013 13:50:32 +0100
From:	Tomasz Figa <tomasz.figa@...il.com>
To:	Maxime Ripard <maxime.ripard@...e-electrons.com>
Cc:	Chen-Yu Tsai <wens@...e.org>,
	Mike Turquette <mturquette@...aro.org>,
	Giuseppe Cavallaro <peppe.cavallaro@...com>,
	netdev@...r.kernel.org, Rob Herring <rob.herring@...xeda.com>,
	devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
	linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com,
	Srinivas Kandagatla <srinivas.kandagatla@...com>
Subject: Re: [PATCH 04/10] net: stmmac: sunxi platfrom extensions for GMAC in Allwinner A20 SoC's

On Saturday 07 of December 2013 12:46:16 Maxime Ripard wrote:
> On Sat, Dec 07, 2013 at 12:12:26PM +0100, Tomasz Figa wrote:
> > On Saturday 07 of December 2013 11:27:10 Maxime Ripard wrote:
> > > Chen-Yu, Mike,
> > > 
> > > On Sat, Dec 07, 2013 at 01:29:37AM +0800, Chen-Yu Tsai wrote:
> > > > The Allwinner A20 has an ethernet controller that seems to be
> > > > an early version of Synopsys DesignWare MAC 10/100/1000 Universal,
> > > > which is supported by the stmmac driver.
> > > > 
> > > > Allwinner's GMAC requires setting additional registers in the SoC's
> > > > clock control unit.
> > > > 
> > > > The exact version of the DWMAC IP that Allwinner uses is unknown,
> > > > thus the exact feature set is unknown.
> > > > 
> > > > Signed-off-by: Chen-Yu Tsai <wens@...e.org>
> > > > ---
> > > >  .../bindings/net/allwinner,sun7i-gmac.txt          | 22 +++++++
> > > >  drivers/net/ethernet/stmicro/stmmac/Kconfig        | 12 ++++
> > > >  drivers/net/ethernet/stmicro/stmmac/Makefile       |  1 +
> > > >  drivers/net/ethernet/stmicro/stmmac/dwmac-sunxi.c  | 76 ++++++++++++++++++++++
> > > >  drivers/net/ethernet/stmicro/stmmac/stmmac.h       |  3 +
> > > >  .../net/ethernet/stmicro/stmmac/stmmac_platform.c  |  3 +
> > > >  6 files changed, 117 insertions(+)
> > > > 
> > > > diff --git a/Documentation/devicetree/bindings/net/allwinner,sun7i-gmac.txt b/Documentation/devicetree/bindings/net/allwinner,sun7i-gmac.txt
> > > > new file mode 100644
> > > > index 0000000..271554a
> > > > --- /dev/null
> > > > +++ b/Documentation/devicetree/bindings/net/allwinner,sun7i-gmac.txt
> > > > @@ -0,0 +1,22 @@
> > > > +* Allwinner GMAC ethernet controller
> > > > +
> > > > +This device is a platform glue layer for stmmac.
> > > > +Please see stmmac.txt for the other unchanged properties.
> > > > +
> > > > +Required properties:
> > > > + - compatible:  Should be "allwinner,sun7i-gmac"
> > > 
> > > Please use sun7i-a20-gmac here.
> > > 
> > > > + - reg: Address and length of register set for the device and corresponding
> > > > +   clock control
> > > >
> > > > +Examples:
> > > > +
> > > > +	gmac: ethernet@...50000 {
> > > > +		compatible = "allwinner,sun7i-gmac";
> > > > +		reg = <0x01c50000 0x10000>,
> > > > +		      <0x01c20164 0x4>;
> > > 
> > > This is actually a clock, and should probably be registered in the
> > > common clock framework.
> > > 
> > > Mike: This small register actually is a regular muxer/divider, except
> > > that it has some bits that are of interest to the ethernet controller
> > > (for example to set wether it's using GMII or RGMII to communicate
> > > with the phy), that, as far as I'm aware of, aren't really fitting
> > > into the CCF.
> > > 
> > > Do you have some recommendation on how to proceed?
> > > 
> > > Maybe make a thin "real" clock driver in this hardware glue, that
> > > provides !exported function to set this *GMII thing.
> > 
> > Is this register part of a bigger IP block that manages clocks for other
> > IP blocks than stmmac as well? If not, I don't see a point of exporting
> > a clock from inside of the GMAC "domain" just to feed it back into it
> > as the only user.
> 
> This register is actually part of the SoC clock controller. So it sits
> right beside the other clocks registers controlling the clocks of the
> other devices, and is not part of the GMAC IP itself.

Is there any description for GMAC_IF_TYPE_RGMII and GMAC_TX_CLK fields?

Name of the latter sounds like a normal clock mux, but the former is
just a mystery (especially why it is a part of the clock controller).

Best regards,
Tomasz

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