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

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Message-ID: <YxeBCsA32jnwMjSj@nvidia.com>
Date:   Tue, 6 Sep 2022 14:19:06 -0300
From:   Jason Gunthorpe <jgg@...dia.com>
To:     Nipun Gupta <nipun.gupta@....com>
Cc:     robh+dt@...nel.org, krzysztof.kozlowski+dt@...aro.org,
        gregkh@...uxfoundation.org, rafael@...nel.org,
        eric.auger@...hat.com, alex.williamson@...hat.com,
        cohuck@...hat.com, puneet.gupta@....com,
        song.bao.hua@...ilicon.com, mchehab+huawei@...nel.org,
        maz@...nel.org, f.fainelli@...il.com, jeffrey.l.hugo@...il.com,
        saravanak@...gle.com, Michael.Srba@...nam.cz, mani@...nel.org,
        yishaih@...dia.com, robin.murphy@....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, harpreet.anand@....com,
        nikhil.agarwal@....com, michal.simek@....com,
        aleksandar.radovanovic@....com, git@....com
Subject: Re: [RFC PATCH v3 4/7] bus/cdx: add cdx-MSI domain with gic-its
 domain as parent

On Tue, Sep 06, 2022 at 07:17:58PM +0530, Nipun Gupta wrote:

> +static void cdx_msi_write_msg(struct irq_data *irq_data,
> +			      struct msi_msg *msg)
> +{
> +	/*
> +	 * Do nothing as CDX devices have these pre-populated
> +	 * in the hardware itself.
> +	 */
> +}

Huh?

There is no way it can be pre-populated, the addr/data pair,
especially on ARM, is completely under SW control. There is some
commonly used IOVA base in Linux for the ITS page, but no HW should
hardwire that.

Jason