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

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

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.

> +
>  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.

Thanks, Roger.