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

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Date:   Tue, 29 Sep 2020 16:53:47 +0100
From:   Grant Likely <grant.likely@....com>
To:     Andrew Lunn <andrew@...n.ch>,
        Calvin Johnson <calvin.johnson@....nxp.com>
Cc:     "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 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.

g.