linux-kernel - RE: [RFC PATCH v3 4/7] bus/cdx: add cdx-MSI domain with gic-its domain as parent

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Date:   Fri, 14 Oct 2022 12:13:45 +0000
From:   "Radovanovic, Aleksandar" <aleksandar.radovanovic@....com>
To:     "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>
CC:     Jason Gunthorpe <jgg@...pe.ca>,
        "Gupta, Nipun" <Nipun.Gupta@....com>,
        Marc Zyngier <maz@...nel.org>,
        Robin Murphy <robin.murphy@....com>,
        "robh+dt@...nel.org" <robh+dt@...nel.org>,
        "krzysztof.kozlowski+dt@...aro.org" 
        <krzysztof.kozlowski+dt@...aro.org>,
        "rafael@...nel.org" <rafael@...nel.org>,
        "eric.auger@...hat.com" <eric.auger@...hat.com>,
        "alex.williamson@...hat.com" <alex.williamson@...hat.com>,
        "cohuck@...hat.com" <cohuck@...hat.com>,
        "Gupta, Puneet (DCG-ENG)" <puneet.gupta@....com>,
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        "Anand, Harpreet" <harpreet.anand@....com>,
        "Agarwal, Nikhil" <nikhil.agarwal@....com>,
        "Simek, Michal" <michal.simek@....com>,
        "git (AMD-Xilinx)" <git@....com>
Subject: RE: [RFC PATCH v3 4/7] bus/cdx: add cdx-MSI domain with gic-its
 domain as parent

[AMD Official Use Only - General]



> -----Original Message-----
> From: gregkh@...uxfoundation.org <gregkh@...uxfoundation.org>
> Sent: 14 October 2022 12:55
> To: Radovanovic, Aleksandar <aleksandar.radovanovic@....com>
> Cc: Jason Gunthorpe <jgg@...pe.ca>; Gupta, Nipun
> <Nipun.Gupta@....com>; Marc Zyngier <maz@...nel.org>; Robin Murphy
> <robin.murphy@....com>; robh+dt@...nel.org;
> krzysztof.kozlowski+dt@...aro.org; rafael@...nel.org;
> eric.auger@...hat.com; alex.williamson@...hat.com; cohuck@...hat.com;
> Gupta, Puneet (DCG-ENG) <puneet.gupta@....com>;
> song.bao.hua@...ilicon.com; mchehab+huawei@...nel.org;
> f.fainelli@...il.com; jeffrey.l.hugo@...il.com; saravanak@...gle.com;
> Michael.Srba@...nam.cz; mani@...nel.org; yishaih@...dia.com;
> will@...nel.org; joro@...tes.org; masahiroy@...nel.org;
> ndesaulniers@...gle.com; linux-arm-kernel@...ts.infradead.org; linux-
> kbuild@...r.kernel.org; linux-kernel@...r.kernel.org;
> devicetree@...r.kernel.org; kvm@...r.kernel.org; okaya@...nel.org;
> Anand, Harpreet <harpreet.anand@....com>; Agarwal, Nikhil
> <nikhil.agarwal@....com>; Simek, Michal <michal.simek@....com>; git
> (AMD-Xilinx) <git@....com>
> Subject: Re: [RFC PATCH v3 4/7] bus/cdx: add cdx-MSI domain with gic-its
> domain as parent
> 
> Caution: This message originated from an External Source. Use proper
> caution when opening attachments, clicking links, or responding.
> 
> 
> On Fri, Oct 14, 2022 at 11:18:36AM +0000, Radovanovic, Aleksandar wrote:
> > Anyway, I think we're straying off topic here, none of this is visible to the
> kernel anyway. The question that we still need to answer is, are you OK with
> the limitations I listed originally?
> 
> What original limitations?  

Limitations with regards to MSI message configuration of a CDX device:

1) MSI write value is at most 16 useable bits

2) MSI address value must be the same across all vectors of a single CDX device
This would be the (potentially IOMMU translated) I/O address of
GITS_TRANSLATER. As long as that IOMMU translation is consistent across a 
single device, I think we should be OK.

> This thread is crazy and complex and you need to
> use your \n key more :)

I do try, but the corporate mail client that we're stuck with seems to just merge
everything back together. Sigh.

> thanks,
> 
> greg k-h