From: Rahul Singh <Rahul.Singh@arm.com>
To: Jan Beulich <jbeulich@suse.com>
Cc: Bertrand Marquis <Bertrand.Marquis@arm.com>,
Paul Durrant <paul@xen.org>,
Andrew Cooper <andrew.cooper3@citrix.com>,
George Dunlap <george.dunlap@citrix.com>,
Ian Jackson <iwj@xenproject.org>, Julien Grall <julien@xen.org>,
Stefano Stabellini <sstabellini@kernel.org>, Wei Liu <wl@xen.org>,
Daniel De Graaf <dgdegra@tycho.nsa.gov>,
"xen-devel@lists.xenproject.org" <xen-devel@lists.xenproject.org>
Subject: Re: [PATCH v4 3/3] xen/pci: Refactor MSI code that implements MSI functionality within XEN
Date: Wed, 5 May 2021 16:09:04 +0000 [thread overview]
Message-ID: <95E9A7E3-D13B-4DFD-8423-5951BB6976BB@arm.com> (raw)
In-Reply-To: <bbc50008-da47-a5e2-501b-a9c06ce38335@suse.com>
Hi Jan,
> On 3 May 2021, at 3:46 pm, Jan Beulich <jbeulich@suse.com> wrote:
>
> On 29.04.2021 16:46, Rahul Singh wrote:
>> MSI code that implements MSI functionality to support MSI within XEN is
>> not usable on ARM. Move the code under CONFIG_HAS_PCI_MSI_INTERCEPT flag
>> to gate the code for ARM.
>>
>> Currently, we have no idea how MSI functionality will be supported for
>> other architecture therefore we have decided to move the code under
>> CONFIG_PCI_MSI_INTERCEPT. We know this is not the right flag to gate the
>> code but to avoid an extra flag we decided to use this.
>
> My objection remains: Actively putting code under the wrong gating
> CONFIG_* is imo quite a bit worse than keeping it under a too wide one
> (e.g. CONFIG_X86), if introducing a separate CONFIG_HAS_PCI_MSI is
> deemed undesirable for whatever reason. Otherwise every abuse of
> CONFIG_PCI_MSI_INTERCEPT ought to get a comment to the effect of this
> being an abuse, which in particular for code you move into
> xen/drivers/passthrough/msi-intercept.c would end up sufficiently odd.
> (As a minor extra remark, putting deliberately misplaced code at the
> top of a file rather than at its bottom is likely to add to possible
> confusion down the road.)
>
I understand that this is not the correct flag to gate the code. If we choose to
move the code under CONFIG_X86 there will be #ifdef in the common file
"passthrough/pci.c” that I think will make code harder to understand. The only
option left is to introduce the new CONFIG_HAS_PCI_MSI option and new
non-arch files (msi.c, msi.h). Move all non-intercept-related code to those files.
As I mention earlier also this is code and as of now we have no data on how MSI
will be supported for non-x86 architecture that’s why we decided it is better to move
the code under CONFIG_PCI_MSI_INTERCEPT and later point in time we can
modify the code once non-x86 architecture implements MSI functionality in XEN if required.
I will move the code at the bottom of the file to avoid confusion.
Regards,
Rahul
> Jan
prev parent reply other threads:[~2021-05-05 16:09 UTC|newest]
Thread overview: 8+ messages / expand[flat|nested] mbox.gz Atom feed top
2021-04-29 14:46 [PATCH v4 0/3] xen/pci: Make PCI passthrough code non-x86 specific Rahul Singh
2021-04-29 14:46 ` [PATCH v4 1/3] xen/iommu: Move iommu_update_ire_from_msi(..) to xen/iommu.h Rahul Singh
2021-04-29 14:46 ` [PATCH v4 2/3] xen/pci: Refactor PCI MSI intercept related code Rahul Singh
2021-05-03 14:38 ` Jan Beulich
2021-05-05 7:51 ` Rahul Singh
2021-04-29 14:46 ` [PATCH v4 3/3] xen/pci: Refactor MSI code that implements MSI functionality within XEN Rahul Singh
2021-05-03 14:46 ` Jan Beulich
2021-05-05 16:09 ` Rahul Singh [this message]
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