linux-kernel - Re: [PATCHv2 0/3] arm64 xilinx zynqmp firmware interface

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Date:   Thu, 17 Aug 2017 12:32:25 +0200
From:   Michal Simek <michal.simek@...inx.com>
To:     Sudeep Holla <sudeep.holla@....com>,
        Michal Simek <michal.simek@...inx.com>,
        <linux-arm-kernel@...ts.infradead.org>
CC:     Marc Zyngier <marc.zyngier@....com>, Arnd Bergmann <arnd@...db.de>,
        <edgar.iglesias@...inx.com>, Rob Herring <robh@...nel.org>,
        Punnaiah Choudary Kalluri 
        <punnaiah.choudary.kalluri@...inx.com>,
        Jean Delvare <jdelvare@...e.de>,
        Dinh Nguyen <dinguyen@...nsource.altera.com>,
        Rob Herring <robh+dt@...nel.org>,
        Tero Kristo <t-kristo@...com>,
        Catalin Marinas <catalin.marinas@....com>,
        Olof Johansson <olof@...om.net>,
        Sören Brinkmann <soren.brinkmann@...inx.com>,
        Kevin Hilman <khilman@...libre.com>,
        Nishanth Menon <nm@...com>,
        Thierry Reding <treding@...dia.com>,
        Kevin Brodsky <kevin.brodsky@....com>,
        Will Deacon <will.deacon@....com>,
        <devicetree@...r.kernel.org>, Alexander Graf <agraf@...e.de>,
        Moritz Fischer <mdf@...nel.org>,
        Michal Simek <monstr@...str.eu>,
        Mark Rutland <mark.rutland@....com>,
        Carlo Caione <carlo@...lessm.com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        <linux-kernel@...r.kernel.org>,
        "Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>
Subject: Re: [PATCHv2 0/3] arm64 xilinx zynqmp firmware interface

On 17.8.2017 11:12, Sudeep Holla wrote:
> 
> 
> On 17/08/17 09:42, Michal Simek wrote:
>> On 17.8.2017 09:52, Marc Zyngier wrote:
>>> On 17/08/17 07:10, Michal Simek wrote:
>>>> On 16.8.2017 17:39, Marc Zyngier wrote:
>>>>> On 16/08/17 13:24, Michal Simek wrote:
>>>>>> Hi,
>>>>>>
>>>>>> xilinx is using this interface for very long time and we can't merge our
>>>>>> driver changes to Linux because of missing communication layer with
>>>>>> firmware. This interface was developed before scpi and scmi was
>>>>>> available. In connection to power management scpi and scmi are missing
>>>>>> pieces which we already use. There is a separate discussion how to
>>>>>> extend scmi to support all our use cases.
>>>>>
>>>>> So maybe we should wait and see where this discussion is going before we
>>>>> merge yet another firmware interface?
>>>>
>>>> It will take a lot of time when this discussion ends and I can't see any
>>>> benefit to hold all
>>>
>>> Well, so far, the benefit of this series is exactly nil, as the code it
>>> brings is *unused*. It is impossible to review in isolation.
>>>
>>
>> Ok. I will add others drivers to this series that's not a problem.
>>
>>> In the meantime, you can continue finding out how *not* to have to merge
>>> this code, and instead focus on using the infrastructure we already
>>> have, or at least influence the infrastructure that is being designed.
>>> It will be much better than dumping yet another slab of "I'm so
>>> different" code that is going to ultimately bitrot.
>>
>> I am happy to look the better proposed way. SCPI is ancient and SCMI is
>> replacement and not merged yet. We already had a call with arm and
>> Sudeep was on it too where outcome from that was that we can't use that
>> because it doesn't support what we need to support now.
>>
> 
> OK, none of the specifics were discussed in the meeting to conclude that
> SCMI can't be used. My takeaway from the meeting was Xilinx has this
> interface for long and being deployed in various systems. I would like
> to get into specifics before discarding SCMI as unusable. What bothers
> me more is that why was that not raised during the specification review
> which was quite a long period IMO ? I tend to think Xilinx never
> bothered to look/review the specification as this f/w interface was
> already there.

Xilinx is using this interface from Aug 2015. I am not aware about any
invitation to spec review. And not sure who was there from xilinx.

> 
> However I still can't see why this was posted once we started pushing
> out SCMI patches especially given that this f/w interface was there for
> long and no attempts were made in past to upstream this.

The reason is simple which is upstream our code which depends on this
communication layer. I don't think there is quick path to move to
different interface than this one.

> 
> Also I am not dismissing the series yet, but if I find that SCMI can be
> used(after getting specifics from this series myself), I will at-least
> argue against the "SCMI can't be used" argument.

This is not my argument that we can't use SCMI. This is what was my
understanding from that meeting we had. And definitely there is no quick
path for us to switch to SCMI and breaks all current existing customers.

And this interface is just in the same position as current SCPI. It
means you have SCPI already merged and you are adding new one. SCMI
could be maybe also just SCPIv2.
And when it is merged you are going to move all targets to this new
interface. The same is for us but instead of scpi it is this interface
we use and test.

Thanks,
Michal