RE: [PATCH v3 17/35] x86/pci/xen: Use msi_msg shadow structs

David Laight
2020-10-25T09:49:13Z

From: David Woodhouse
> Sent: 24 October 2020 22:35
>
> From: Thomas Gleixner <tglx@linutronix.de>
>
> Use the msi_msg shadow structs and compose the message with named bitfields
> instead of the unreadable macro maze.
>
> Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
> Signed-off-by: David Woodhouse <dwmw@amazon.co.uk>
> ---
> arch/x86/pci/xen.c | 26 +++++++++++---------------
> 1 file changed, 11 insertions(+), 15 deletions(-)
>
> diff --git a/arch/x86/pci/xen.c b/arch/x86/pci/xen.c
> index c552cd2d0632..3d41a09c2c14 100644
> --- a/arch/x86/pci/xen.c
> +++ b/arch/x86/pci/xen.c
> @@ -152,7 +152,6 @@ static int acpi_register_gsi_xen(struct device *dev, u32 gsi,
>
> #if defined(CONFIG_PCI_MSI)
> #include <linux/msi.h>
> -#include <asm/msidef.h>
>
> struct xen_pci_frontend_ops *xen_pci_frontend;
> EXPORT_SYMBOL_GPL(xen_pci_frontend);
> @@ -210,23 +209,20 @@ static int xen_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
> return ret;
> }
>
> -#define XEN_PIRQ_MSI_DATA (MSI_DATA_TRIGGER_EDGE | \
> - MSI_DATA_LEVEL_ASSERT | (3 << 8) | MSI_DATA_VECTOR(0))
> -
> static void xen_msi_compose_msg(struct pci_dev *pdev, unsigned int pirq,
> struct msi_msg *msg)
> {
> - /* We set vector == 0 to tell the hypervisor we don't care about it,
> - * but we want a pirq setup instead.
> - * We use the dest_id field to pass the pirq that we want. */
> - msg->address_hi = MSI_ADDR_BASE_HI | MSI_ADDR_EXT_DEST_ID(pirq);
> - msg->address_lo =
> - MSI_ADDR_BASE_LO |
> - MSI_ADDR_DEST_MODE_PHYSICAL |
> - MSI_ADDR_REDIRECTION_CPU |
> - MSI_ADDR_DEST_ID(pirq);
> -
> - msg->data = XEN_PIRQ_MSI_DATA;
> + /*
> + * We set vector == 0 to tell the hypervisor we don't care about
> + * it, but we want a pirq setup instead. We use the dest_id fields
> + * to pass the pirq that we want.
> + */
> + memset(msg, 0, sizeof(*msg));
> + msg->address_hi = X86_MSI_BASE_ADDRESS_HIGH;
> + msg->arch_addr_hi.destid_8_31 = pirq >> 8;
> + msg->arch_addr_lo.destid_0_7 = pirq & 0xFF;
> + msg->arch_addr_lo.base_address = X86_MSI_BASE_ADDRESS_LOW;
> + msg->arch_data.delivery_mode = APIC_DELIVERY_MODE_EXTINT;
> }

Just looking at a random one of these patches...

Does the compiler manage to optimise that reasonably?
Or does it generate a lot of shifts and masks as each
bitfield is set?

The code generation for bitfields is often a lot worse
that that for |= setting bits in a word.

David

-
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