linux-kernel - Re: [PATCH 2/2] arm64: dts: juno: Describe the full GICv2m region

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Date:   Wed, 28 Feb 2018 15:48:42 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Robin Murphy <robin.murphy@....com>,
        Marc Zyngier <marc.zyngier@....com>,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        Liviu Dudau <liviu.dudau@....com>
Cc:     Sudeep Holla <sudeep.holla@....com>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [PATCH 2/2] arm64: dts: juno: Describe the full GICv2m region



On 12/02/18 19:17, Robin Murphy wrote:
> On 12/02/18 18:27, Marc Zyngier wrote:
>> Hi Sudeep,
>>
>> On 12/02/18 18:17, Sudeep Holla wrote:
>>>
>>>
>>> On 07/02/18 14:32, Marc Zyngier wrote:
>>>> From: Robin Murphy <robin.murphy@....com>
>>>>
>>>> Juno's GICv2m implementation consists of four frames providing 32
>>>> interrupts each. Since it is possible to plug in enough PCIe endpoints
>>>> to consume more than 32 MSIs, and the driver already has a bodge to
>>>> handle multiple frames, let's expose the other three as well.
>>>>
>>>
>>> Change on it own looks good. So if you want to merge via your tree:
>>>
>>> Acked-by: Sudeep Holla <sudeep.holla@....com>
>>>
>>> Let me know if you decide not to take it via your tree and you want me
>>> to send it to arm-soc.
>>
>> If this would usually go via arm-soc, feel free to take it via this
>> route. I'll drop the patch from my tree.
>>
>>> On the side note I just noticed the Juno TRM[1] has 64k for each of
>>> these MSI frames(page 3-24 section 3.3.5 Application memory map summary)
>>>
>>> I am not sure if TRM is wrong. This patch is just copying the 4k size
>>> from frame 0 which got added with initial Juno DTS.
>>
>> I can't see why the TRM would be wrong. This is actually consistent with
>> the expected practice of aligning all devices on a 64kB boundary and
>> size so that you don't get any nasty surprise when passing the device to
>> a VM (*cough* GIC400 *cough*).
>>
>> Robin, any chance you could check this?
> 
> Well, the engineering spec for the v2m widget does claim that only the
> bottom 12 bits of AxADDR are used, but on the other hand it also implies
> that the "real" endpoint here is a single monolithic block of 4 such
> widgets, so a third truth is that there is only a single 256KB region...
> 
> As usual, I've completely forgotten about virtualisation when it comes
> to hardware :) On reflection I do of course appreciate that whilst 60KB
> of RAZ/WI space isn't significant in terms of "a device", it is rather
> more so in terms of "not a device" - if the only reasonable way to
> communicate that is to describe the v2m devices each owning 64KB, then
> I'm quite happy for you to fix up the patch that way if you want.
> 

I have applied this patch as is [1] and added another patch to fix the
size to 64kB for all the frames on top as per Juno TRM. Sorry, I forgot
to send that out, will do that shortly.

-- 
Regards,
Sudeep

[1] https://git.kernel.org/sudeep.holla/linux/h/for-next/juno