linux-kernel - Re: [PATCH v2 0/2] net: thunder: Add ACPI support.

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Message-ID: <55CB67E4.8030001@caviumnetworks.com>
Date:	Wed, 12 Aug 2015 08:36:04 -0700
From:	David Daney <ddaney@...iumnetworks.com>
To:	Catalin Marinas <catalin.marinas@....com>
CC:	David Miller <davem@...emloft.net>, <mark.rutland@....com>,
	<linux-mips@...ux-mips.org>, <rafael@...nel.org>,
	<netdev@...r.kernel.org>, <david.daney@...ium.com>,
	<linux-kernel@...r.kernel.org>, <tomasz.nowicki@...aro.org>,
	<rrichter@...ium.com>, <linux-acpi@...r.kernel.org>,
	<ddaney.cavm@...il.com>, <sgoutham@...ium.com>,
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH v2 0/2] net: thunder: Add ACPI support.

On 08/12/2015 08:23 AM, Catalin Marinas wrote:
> On Tue, Aug 11, 2015 at 01:04:55PM -0700, David Daney wrote:
>> On 08/11/2015 11:49 AM, David Miller wrote:
>>> From: David Daney <ddaney.cavm@...il.com>
>>> Date: Mon, 10 Aug 2015 17:58:35 -0700
>>>
>>>> Change from v1:  Drop PHY binding part, use fwnode_property* APIs.
>>>>
>>>> The first patch (1/2) rearranges the existing code a little with no
>>>> functional change to get ready for the second.  The second (2/2) does
>>>> the actual work of adding support to extract the needed information
>>> >from the ACPI tables.
>>>
>>> Series applied.
>>
>> Thank you very much.
>>
>>> In the future it might be better structured to try and get the OF
>>> node, and if that fails then try and use the ACPI method to obtain
>>> these values.
>>
>> Our current approach, as you can see in the patch, is the opposite.  If ACPI
>> is being used, prefer that over the OF device tree.
>>
>> You seem to be recommending precedence for OF.  It should be consistent
>> across all drivers/sub-systems, so do you really think that OF before ACPI
>> is the way to go?
>
> On arm64 (unless you use a vendor kernel), DT takes precedence over ACPI
> if both arm provided to the kernel (and it's a fair assumption given
> that ACPI on ARM is still in the early days). You could also force ACPI
> with acpi=force on the kernel cmd line and the arch code will not
> unflatten the DT even if it is provided, therefore is_of_node(fwnode)
> returning false.
>
> I haven't looked at your driver in detail but something like AMD's
> xgbe_probe() uses a single function for both DT and ACPI with
> device_property_read_*() functions getting the information from the
> correct place in either case. The ACPI vs DT precedence is handled by
> the arch boot code, we never mix the two and confuse the drivers.
>

My long term plan is to create something like 
firmware_get_mac_address(), that would encapsulate  of_get_mac_address() 
and the ACPI equivalent.

Same for firmware_phy_find_device().

These would function as you suggest, but lacking this infrastructure, we 
implemented this patch set instead.

Thanks,
David Daney
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