[PATCH] powerpc/pseries/msi: Add an empty irq_write_msi_msg() handler

[Mahesh J Salgaonkar]

On 2021-09-30 12:25:35 Thu, Cédric Le Goater wrote:
> 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 95fecd90397e ("ipr: add test for MSI interrupt support") as an
> improvement of commit 5a9ef25b14d3 ("[SCSI] ipr: add MSI support")
> because a boot failure was reported on a Bimini PowerPC system :
> 
>   https://x-lore.kernel.org/all/1242926159.3007.5.camel@localhost.localdomain/
> 
> It was finally decided to remove MSI support on Bimini systems in
> 6eb0ac03899a ("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.
> 
> Cc: Wen Xiong <wenxiong at linux.vnet.ibm.com>
> Cc: Douglas Miller <dougmill at linux.vnet.ibm.com>
> Cc: Brian King <brking at linux.vnet.ibm.com>
> Fixes: a5f3d2c17b07 ("powerpc/pseries/pci: Add MSI domains")
> Signed-off-by: Cédric Le Goater <clg at kaod.org>

Tested-by: Mahesh Salgaonkar <mahesh at linux.ibm.com>

This fixes the issue reported at
https://lore.kernel.org/linuxppc-dev/65f0085f-c6a9-e3ea-4d60-fcf09b7c7360@linux.vnet.ibm.com/T/#u
by Abdul.

Thanks,
-- 
Mahesh J Salgaonkar