linux-kernel - Re: [PATCH v6 1/5] iommu: Return -EMEDIUMTYPE for incompatible domain and device/group

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Message-ID: <YxiRkm7qgQ4k+PIG@8bytes.org>
Date:   Wed, 7 Sep 2022 14:41:54 +0200
From:   Joerg Roedel <joro@...tes.org>
To:     Nicolin Chen <nicolinc@...dia.com>
Cc:     will@...nel.org, robin.murphy@....com, alex.williamson@...hat.com,
        suravee.suthikulpanit@....com, marcan@...can.st,
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        dwmw2@...radead.org, baolu.lu@...ux.intel.com,
        mjrosato@...ux.ibm.com, gerald.schaefer@...ux.ibm.com,
        orsonzhai@...il.com, baolin.wang@...ux.alibaba.com,
        zhang.lyra@...il.com, thierry.reding@...il.com, vdumpa@...dia.com,
        jonathanh@...dia.com, jean-philippe@...aro.org, cohuck@...hat.com,
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        christophe.jaillet@...adoo.fr, yangyingliang@...wei.com,
        jon@...id-run.com, iommu@...ts.linux.dev,
        linux-kernel@...r.kernel.org, asahi@...ts.linux.dev,
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        kevin.tian@...el.com
Subject: Re: [PATCH v6 1/5] iommu: Return -EMEDIUMTYPE for incompatible
 domain and device/group

On Mon, Aug 15, 2022 at 11:14:33AM -0700, Nicolin Chen wrote:
> Provide a dedicated errno from the IOMMU driver during attach that the
> reason attached failed is because of domain incompatability. EMEDIUMTYPE
> is chosen because it is never used within the iommu subsystem today and
> evokes a sense that the 'medium' aka the domain is incompatible.

I am not a fan of re-using EMEDIUMTYPE or any other special value. What
is needed here in EINVAL, but with a way to tell the caller which of the
function parameters is actually invalid.

For that I prefer adding an additional pointer parameter to the attach
functions in which the reason for the failure can be communicated up the
chain.

For the top-level iommu_attach_device() function I am okay with having a
special version which has this additional paremter.

Regards,

	Joerg