linux-kernel - Re: [PATCH 2/3] devicetree: add binding for Aurora VLSI NB8800 Ethernet controller

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Date:	Fri, 23 Oct 2015 15:06:06 +0100
From:	Måns Rullgård <mans@...sr.com>
To:	Marc Gonzalez <marc_gonzalez@...madesigns.com>
Cc:	DT <devicetree@...r.kernel.org>, Kumar Gala <galak@...eaurora.org>,
	Rob Herring <robh+dt@...nel.org>,
	Pawel Moll <pawel.moll@....com>,
	Mark Rutland <mark.rutland@....com>,
	Ian Campbell <ijc+devicetree@...lion.org.uk>,
	<linux-kernel@...r.kernel.org>,
	Sebastian Frias <sebastian_frias@...madesigns.com>,
	Thibaud Cornic <thibaud_cornic@...madesigns.com>,
	Mason <slash.tmp@...e.fr>
Subject: Re: [PATCH 2/3] devicetree: add binding for Aurora VLSI NB8800 Ethernet controller

Marc Gonzalez <marc_gonzalez@...madesigns.com> writes:

> On 23/10/2015 15:41, Måns Rullgård wrote:
>
>> Marc Gonzalez wrote:
>> 
>>> On 22/10/2015 16:02, Mans Rullgard wrote:
>>>
>>>> This adds a binding for the Aurora VLSI NB8800 Ethernet controller
>>>> using the "aurora,nb8800" compatible string.  When used in Sigma
>>>> Designs chips a few additional control registers are available.
>>>> This variant is indicated by the "sigma,smp8640-ethernet" compatible
>>>> string.
>>>>
>>>> Signed-off-by: Mans Rullgard <mans@...sr.com>
>>>> ---
>>>>  .../devicetree/bindings/net/aurora,nb8800.txt      | 26 ++++++++++++++++++++++
>>>>  1 file changed, 26 insertions(+)
>>>>  create mode 100644 Documentation/devicetree/bindings/net/aurora,nb8800.txt
>>>>
>>>> diff --git a/Documentation/devicetree/bindings/net/aurora,nb8800.txt b/Documentation/devicetree/bindings/net/aurora,nb8800.txt
>>>> new file mode 100644
>>>> index 0000000..c19f615
>>>> --- /dev/null
>>>> +++ b/Documentation/devicetree/bindings/net/aurora,nb8800.txt
>>>> @@ -0,0 +1,26 @@
>>>> +* Aurora VLSI AU-NB8800 Ethernet controller
>>>> +
>>>> +Required properties:
>>>> +- compatible: Should be "aurora,nb8800", "sigma,smp8640-ethernet"
>>>> +	The latter indicates presence of extra features added by Sigma Designs.
>>>
>>> I've been meaning to ask a noob question to the devicetree group
>>> about how names for compatible strings are chosen.
>>>
>>> Sigma Designs has two active SoC families, Tango3 (which consists of
>>> about a dozen MIPS-based SoCs, typically named SMP86xx) and Tango4
>>> (a few ARM-based SoCs, typically named SMP87xx). I should note that
>>> there is no SMP8640 SoC AFAIK, rather SMP864x is a Tango3 sub-family
>>> (I could locate 42,43,44,45,46).
>>>
>>> AFAIK, all our SoCs are using the same Aurora NB8800 Ethernet MAC,
>>> along with the extra features. I find it odd to use a specific SoC
>>> model to refer to this device, instead of a more generic name.
>>> (It's weird having to mention smp8640 in the tango4 DT.)
>> 
>> I picked 8640 since all 8640 or higher chips are compatible (863x chips
>> (tango2) are not).  Some of the later versions have additional extra
>> features, but they all work with the basic driver.
>> 
>> There also appear to be some differences (bug fixes?) between 8643 and
>> 8759 (the ones I have) not documented anywhere.
>
> I'm trying to locate someone who would know these kinds of details.

More specifically, the DMA completion interrupts seem to behave
differently.

>>> I thought one had to specify also whether the device sent "edge"
>>> or "level" IRQs?
>> 
>> Depends on the interrupt controller.  This is just an example.
>
> Sorry for the noise. (I thought edge/level was a device property,
> as in "I'll just pulse that IRQ, or I'll hold it until someone
> asks me to shut up.")

Most devices keep the interrupt request line high until explicitly
cleared by a driver.  Whether you want edge or level triggering depends
on the driver design and if the interrupt is shared with other devices.

-- 
Måns Rullgård
mans@...sr.com
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