[PATCH v2] riscv: Kconfig: do not select PCI_MSI if CONIFG_PCI is enabled

[Vincent Chen]

On Wed, Jul 21, 2021 at 1:57 PM Christoph Hellwig <hch at infradead.org> wrote:
>
> On Wed, Jul 21, 2021 at 11:39:12AM +0800, Vincent Chen wrote:
> > The CONFIG_PCI_MSI is used to allow device drivers to enable MSI. The MSI
> > enables a device to generate an interrupt using an inbound Memory Write
> > on its PCI bus instead of asserting a device IRQ pin. The whole mechanism
> > needs support from the PCI controller or generic interrupt controller and
> > the corresponding software driver.
> >
> > The RISC-V Kconfig file actively selects the PCI_MSI  if users enable
> > CONFIG_PCI. However, the RISC-V specification does not require every RISC-V
> > platform shall have MSI support. In other words, Kconfig enables CONFIG_PCI
> > to allow PCI devices to use MSI, but due to lack of MSI support, the kernel
> > may not have any function to deal with the MSI from PCI devices. When this
> > case happens, it leads to the following warning message displayed in
> > booting a v5.10~v5.12 kernel.
>
> So make sure the runtime detection works fine.  An x86 kernel with
> CONFIG_PCI_MSI also works on non-MSI systems.
>
> NAK to this patch.

Thanks for your information. I think this will be a good reference to
solve this warning message for the v5.10~v5.12 riscv kernel. However,
the current RISC-V does not specify that each platform must have a
controller to support PCI_MSI. Even there is no a ratified
specification to provide an interrupt controller to support MSI. In
this circumstance, removing the CONFIG_PCI_MSI selection from the
Kconfig file seems to more close to the RISC-V platform setting. I
guess that is why most architectures, such as ARM and x86, do not add
"select PCI_MSI if PCI" to their Kconfig file. Therefore, I prefer to
remove the "select PCI_MSI if PCI" from the Kconfig file. Please
correct me if I have misunderstands.

Thank you.