netdev - Re: [net-next PATCH v7 1/6] Documentation: ACPI: DSD: Document MDIO PHY

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Date:   Tue, 29 Sep 2020 21:34:43 +0530
From:   Calvin Johnson <calvin.johnson@....nxp.com>
To:     Grant Likely <grant.likely@....com>
Cc:     Andrew Lunn <andrew@...n.ch>,
        "Rafael J . Wysocki" <rafael@...nel.org>,
        Jeremy Linton <jeremy.linton@....com>,
        Russell King - ARM Linux admin <linux@...linux.org.uk>,
        Jon <jon@...id-run.com>,
        Cristi Sovaiala <cristian.sovaiala@....com>,
        Ioana Ciornei <ioana.ciornei@....com>,
        Andy Shevchenko <andy.shevchenko@...il.com>,
        Florian Fainelli <f.fainelli@...il.com>,
        Madalin Bucur <madalin.bucur@....nxp.com>,
        netdev@...r.kernel.org, linux.cj@...il.com,
        linux-acpi@...r.kernel.org, nd <nd@....com>
Subject: Re: [net-next PATCH v7 1/6] Documentation: ACPI: DSD: Document MDIO
 PHY

On Tue, Sep 29, 2020 at 04:53:47PM +0100, Grant Likely wrote:
> 
> 
> On 29/09/2020 14:43, Andrew Lunn wrote:
> > On Tue, Sep 29, 2020 at 10:47:03AM +0530, Calvin Johnson wrote:
> > > Hi Grant,
> > > 
> > > On Fri, Sep 25, 2020 at 02:34:21PM +0100, Grant Likely wrote:
> > > > > +DSDT entry for MDIO node
> > > > > +------------------------
> > > > > +a) Silicon Component
> > > > > +--------------------
> > > > > +	Scope(_SB)
> > > > > +	{
> > > > > +	  Device(MDI0) {
> > > > > +	    Name(_HID, "NXP0006")
> > > > > +	    Name(_CCA, 1)
> > > > > +	    Name(_UID, 0)
> > > > > +	    Name(_CRS, ResourceTemplate() {
> > > > > +	      Memory32Fixed(ReadWrite, MDI0_BASE, MDI_LEN)
> > > > > +	      Interrupt(ResourceConsumer, Level, ActiveHigh, Shared)
> > > > > +	       {
> > > > > +		 MDI0_IT
> > > > > +	       }
> > > > > +	    }) // end of _CRS for MDI0
> > > > > +	    Name (_DSD, Package () {
> > > > > +	      ToUUID("daffd814-6eba-4d8c-8a91-bc9bbf4aa301"),
> > > > > +	      Package () {
> > > > > +		 Package () {"little-endian", 1},
> > > > > +	      }
> > > > 
> > > > Adopting the 'little-endian' property here makes little sense. This looks
> > > > like legacy from old PowerPC DT platforms that doesn't belong here. I would
> > > > drop this bit.
> > > 
> > > I'm unable to drop this as the xgmac_mdio driver relies on this variable to
> > > change the io access to little-endian. Default is big-endian.
> > > Please see:
> > > https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/net/ethernet/freescale/xgmac_mdio.c?h=v5.9-rc7#n55
> > 
> > Hi Calvin
> > 
> > Are we talking about the bus controller endiannes, or the CPU
> > endianness?
> 
> This is orthogonal to the MDIO bus issue. This is a legacy of the xgmac IP
> block originating in PowerPC platforms with a big-endian bus wiring. The
> flag here tells the driver to use little endian when accessing MMIO
> registers.
> 
> > If we are talking about the CPU endiannes, are you plan on supporting
> > any big endian platforms using ACPI? If not, just hard code it.
> > Newbie ACPI question: Does ACPI even support big endian CPUs, given
> > its x86 origins? >
> > If this is the bus controller endianness, are all the SoCs you plan to
> > support via ACPI the same endianness? If they are all the same, you
> > can hard code it.
> 
> I would agree. The ACPI and DT probe paths are different. It would be easy
> to automatically set the little-endian flag by default when xgmac is
> described via ACPI.

Thanks Andrew and Grant for this suggestion. Yes, this is an easy way to solve
this problem. Will do that.

Regards
Calvin