powerpc/pseries/msi: Add an empty irq_write_msi_msg() handler
The IPR drivers tests for MSI support at probe time with MSI vector 0 and when done, frees the IRQ with free_irq(). This test was introduced by 95fecd90 ("ipr: add test for MSI interrupt support") as an improvement of commit 5a9ef25b ("[SCSI] ipr: add MSI support") because a boot failure was reported on a Bimini PowerPC system: https://lore.kernel.org/r/1242926159.3007.5.camel@localhost.localdomain It was finally decided to remove MSI support on Bimini systems in 6eb0ac03 ("powerpc/maple: Add a quirk to disable MSI for IPR on Bimini"). Linux 5.15-rc1 added MSI domain support to the pseries machine and when free_irq is called() in the driver, msi_domain_deactivate() also is. This resets the MSI table entry of the associate vector by calling __pci_write_msi_msg() with an empty message and breaks any further activation of the same vector. In the case of the IPR driver, it breaks the initialization sequence of the IOA. Introduce an empty irq_write_msi_msg() handler in the MSI domain of the pseries machine to avoid clearing the MSI vector entry. Updating the entry is not strictly necessary since it is initialized by the underlying hypervisor, PowerVM or QEMU/KVM. Fixes: a5f3d2c1 ("powerpc/pseries/pci: Add MSI domains") Signed-off-by: Cédric Le Goater <clg@kaod.org> Reported-by: Abdul Haleem <abdhalee@linux.vnet.ibm.com> Tested-by: Mahesh Salgaonkar <mahesh@linux.ibm.com> [mpe: Tweak comment wording and formatting slightly] Signed-off-by: Michael Ellerman <mpe@ellerman.id.au> Link: https://lore.kernel.org/r/20210930102535.1047230-1-clg@kaod.org
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