linux-kernel - Re: [PATCH 3/3] ARM: zynq: DT: Add Ethernet phys

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Date:	Fri, 29 Aug 2014 17:18:07 +0200
From:	Andreas Färber <afaerber@...e.de>
To:	Michal Simek <michal.simek@...inx.com>,
	Florian Fainelli <f.fainelli@...il.com>,
	Jason Gunthorpe <jgunthorpe@...idianresearch.com>
CC:	Sören Brinkmann <soren.brinkmann@...inx.com>,
	Mark Rutland <mark.rutland@....com>,
	"devicetree@...r.kernel.org" <devicetree@...r.kernel.org>,
	Russell King <linux@....linux.org.uk>,
	Pawel Moll <pawel.moll@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	"linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
	Rob Herring <robh+dt@...nel.org>,
	Kumar Gala <galak@...eaurora.org>,
	"linux-arm-kernel@...ts.infradead.org" 
	<linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 3/3] ARM: zynq: DT: Add Ethernet phys

Am 29.08.2014 16:08, schrieb Michal Simek:
> On 08/25/2014 10:21 PM, Florian Fainelli wrote:
>> On 08/25/2014 10:46 AM, Jason Gunthorpe wrote:
>>> On Fri, Aug 22, 2014 at 01:47:09PM -0700, Florian Fainelli wrote:
>>>
>>>>>  - the ID based strings seem to be not needed since, IIUC, the core
>>>>>    reads the ID from the PHY and uses it, so I just left it out not
>>>>>    trying to figure out how to obtain the correct ID
>>>>
>>>> It is not needed, but it is one way to specify a PHY device if you do
>>>> not know what compatible string to use instead.
>>>
>>> No, it is a way to specify a PHY device if the kernel can't auto probe
>>> the Phy ID.
>>>
>>> Last I checked, the kernel doesn't support plain text compatible
>>> strings for phys - everything is driven on the phy id, either auto
>>> probed or specified in the DT.
>>
>> That's right. Some PHY drivers might be relying on specific compatible
>> strings though, but not the core PHY library that probes and maps a
>> driver to a PHY node.
>>
>>>
>>>>>  - the marvell compatible strings are used in our vendor tree. They
>>>>>    aren't used anywhere but in our vendor tree. I though keeping them is
>>>>>    nice since it identifies the PHY fully. And in case that level of
>>>>>    detail is needed at some point it is already there.
>>>>
>>>> And this is the recommended way to do it in case we ever need to key a
>>>> software decision based on the hardware.
>>>
>>> All compatible strings need to be documented.
>>>
>>> .. and they need to encode more information than you get from the phy
>>> id - die revsision, package option, functional options, voltage
>>> codes. Etc.
>>>
>>> .. and they actually need to be *right*
>>
>> Agreed.
>>
>>>
>>> An example: The kernel reports 88E1318S for all four chips in that
>>> family, AFAIK you have to read the package marking to figure out which
>>> you have (it is the same die, with options switched on/off at
>>> packaging time). People have already posted patches trying to
>>> helpfully add a 'marvell,88E1318S' compatible string based on kernel
>>> output. Except it is wrong, it isn't actually the '8S version in the
>>> HW.
>>>
>>> Even worse, Marvell has a whole series of socket compatible phys. Just
>>> because the board the DT author looked at has a '318, doesn't mean
>>> that every board ever made will. We've actually already been switching
>>> between the 318 and 318S for production depending on which has part
>>> availability.
>>>
>>> Basically: don't try to override self-discoverable hardware in DT
>>> without a really good reason.
>>
>> I think that's a very good point, at the very least let's use a
>> compatible string that contains the full 32-bits PHY OUI.
> 
> I think resolution is:
> 1. Do not use marvell,88e1518 because it is not listed anywhere
> 2. Do not add ethernet-phy-idAAAA.BBBB because it breaks autodetection
> if there is different phy on the board and we shouldn't restrict us in this.
> In spite of autodetection takes some time.
> 3. "ethernet-phy-ieee802.3-c22" is optional that's why doesn't need to be added
> 4. Any listed compatible string has to be parsed which takes time
> 
> That's why I think make sense not to use any compatible string.
> This should give us all flexibility which we want to have.

Sorry, but we do need some node that we can reference via phy-handle
from the gem node, don't we?

In that case, is not specifying any compatible string a valid option?

If you don't want to specify the IDs, then I would've assumed we need to
specify the -c22 in order to have *some* compatible string in order to
trigger loading of the appropriate driver module.

Regards,
Andreas

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