Re: [PATCH v4 3/3] xen/pci: Refactor MSI code that implements MSI functionality within XEN

[Jan Beulich <jbeulich@xxxxxxxx>]

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.)

Jan