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Re: [PATCH v3] xen-pciback: Consider INTx disabled when MSI/MSI-X is enabled

To: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>, linux-kernel@xxxxxxxxxxxxxxx

From: Juergen Gross <jgross@xxxxxxxx>

Date: Mon, 16 Oct 2023 08:16:56 +0200

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Cc: Stefano Stabellini <sstabellini@xxxxxxxxxx>, Oleksandr Tyshchenko <oleksandr_tyshchenko@xxxxxxxx>, Jan Beulich <jbeulich@xxxxxxxx>, "moderated list:XEN HYPERVISOR INTERFACE" <xen-devel@xxxxxxxxxxxxxxxxxxxx>

Delivery-date: Mon, 16 Oct 2023 06:17:20 +0000

List-id: Xen developer discussion <xen-devel.lists.xenproject.org>

On 18.11.22 16:49, Marek Marczykowski-Górecki wrote:

Linux enables MSI-X before disabling INTx, but keeps MSI-X masked until
the table is filled. Then it disables INTx just before clearing MASKALL
bit. Currently this approach is rejected by xen-pciback.
According to the PCIe spec, device cannot use INTx when MSI/MSI-X is
enabled (in other words: enabling MSI/MSI-X implicitly disables INTx).

Change the logic to consider INTx disabled if MSI/MSI-X is enabled. This
applies to three places:
  - checking currently enabled interrupts type,
  - transition to MSI/MSI-X - where INTx would be implicitly disabled,
  - clearing INTx disable bit - which can be allowed even if MSI/MSI-X is
    enabled, as device should consider INTx disabled anyway in that case

Fixes: 5e29500eba2a ("xen-pciback: Allow setting PCI_MSIX_FLAGS_MASKALL too")
Signed-off-by: Marek Marczykowski-Górecki <marmarek@xxxxxxxxxxxxxxxxxxxxxx>

Acked-by: Juergen Gross <jgross@xxxxxxxx> Juergen

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