Re: [PATCH v5 07/10] libxl: Only map legacy PCI IRQs if they are supported

[Roger Pau Monné <roger.pau@xxxxxxxxxx>]

On Mon, Oct 25, 2021 at 01:38:19PM +0000, Oleksandr Andrushchenko wrote:
> Hi, Roger!
> 
> On 25.10.21 16:22, Roger Pau Monné wrote:
> > On Fri, Oct 08, 2021 at 08:55:32AM +0300, Oleksandr Andrushchenko wrote:
> >> From: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> >>
> >> Arm's PCI passthrough implementation doesn't support legacy interrupts,
> >> but MSI/MSI-X. This can be the case for other platforms too.
> >> For that reason introduce a new CONFIG_PCI_SUPP_LEGACY_IRQ and add
> >> it to the CFLAGS and compile the relevant code in the toolstack only if
> >> applicable.
> >>
> >> Signed-off-by: Oleksandr Andrushchenko <oleksandr_andrushchenko@xxxxxxxx>
> >> Reviewed-by: Stefano Stabellini <sstabellini@xxxxxxxxxx>
> >> Reviewed-by: Rahul Singh <rahul.singh@xxxxxxx>
> >> Tested-by: Rahul Singh <rahul.singh@xxxxxxx>
> >> ---
> >> Cc: Ian Jackson <iwj@xxxxxxxxxxxxxx>
> >> Cc: Juergen Gross <jgross@xxxxxxxx>
> >>
> >> Since v1:
> >>   - Minimized #idefery by introducing pci_supp_legacy_irq function
> >>     for relevant checks
> >> ---
> >>   tools/libs/light/Makefile    |  4 ++++
> >>   tools/libs/light/libxl_pci.c | 13 +++++++++++++
> >>   2 files changed, 17 insertions(+)
> >>
> >> diff --git a/tools/libs/light/Makefile b/tools/libs/light/Makefile
> >> index 7d8c51d49242..bd3f6be2a183 100644
> >> --- a/tools/libs/light/Makefile
> >> +++ b/tools/libs/light/Makefile
> >> @@ -46,6 +46,10 @@ CFLAGS += -Wno-format-zero-length 
> >> -Wmissing-declarations \
> >>    -Wno-declaration-after-statement -Wformat-nonliteral
> >>   CFLAGS += -I.
> >>   
> >> +ifeq ($(CONFIG_X86),y)
> >> +CFLAGS += -DCONFIG_PCI_SUPP_LEGACY_IRQ
> >> +endif
> > TBH, since CONFIG_PCI_SUPP_LEGACY_IRQ is used in a single place in the
> > source I would consider just using CONFIG_X86, as I think it would be
> > clear enough that some arches support legacy interrupt while others
> > don't. Not sure it's worth going through the obfuscation of defining a
> > separate one.
> The idea behind not using CONFIG_X86 is to be arch agnostic,
> so CONFIG_PCI_SUPP_LEGACY_IRQ makes more sense with this
> respect

I'm not going to insist, but you could have avoided modifying the
Makefile at all by just using:

static bool pci_supp_legacy_irq(void)
{
#ifdef CONFIG_X86
    return true;
#else
    return false;
#endif
}

Which IMO is clearer than the current approach since it's a single
place where CONFIG_PCI_SUPP_LEGACY_IRQ gets used.

> >> +
> >>   SRCS-$(CONFIG_X86) += libxl_cpuid.c
> >>   SRCS-$(CONFIG_X86) += libxl_x86.c
> >>   SRCS-$(CONFIG_X86) += libxl_psr.c
> >> diff --git a/tools/libs/light/libxl_pci.c b/tools/libs/light/libxl_pci.c
> >> index 59f3686fc85e..4c2d7aeefbb2 100644
> >> --- a/tools/libs/light/libxl_pci.c
> >> +++ b/tools/libs/light/libxl_pci.c
> >> @@ -1364,6 +1364,15 @@ static void pci_add_timeout(libxl__egc *egc, 
> >> libxl__ev_time *ev,
> >>       pci_add_dm_done(egc, pas, rc);
> >>   }
> >>   
> >> +static bool pci_supp_legacy_irq(void)
> > A naming more inline with the PCI specification (since we insisted on
> > using ECAM instead of MCFG) would be intx, ie: pci_supports_intx.
> This will require a follow up patch if we all agree this change is needed.
> @Jan, are you ok with the rename?

Didn't realize it was already committed, in which case I guess we could
leave it as-is.

Thanks, Roger.