linux-kernel - Re: [PATCH] pci: tegra: add MSI dependency

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Date:   Wed, 14 Mar 2018 12:45:15 +0100
From:   Thierry Reding <thierry.reding@...il.com>
To:     Arnd Bergmann <arnd@...db.de>
Cc:     Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Manikanta Maddireddy <mmaddireddy@...dia.com>,
        linux-tegra@...r.kernel.org, linux-pci@...r.kernel.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH] pci: tegra: add MSI dependency

On Tue, Mar 13, 2018 at 12:52:05PM +0100, Arnd Bergmann wrote:
> Building the tegra PCIe host driver without MSI results in a link
> failure:
> 
> drivers/pci/host/pci-tegra.o:(.data+0x70): undefined reference to `pci_msi_unmask_irq'
> drivers/pci/host/pci-tegra.o:(.data+0x74): undefined reference to `pci_msi_mask_irq'
> 
> This adds the same dependency that everyone else uses.
> 
> Signed-off-by: Arnd Bergmann <arnd@...db.de>
> ---
>  drivers/pci/host/Kconfig | 1 +
>  1 file changed, 1 insertion(+)

I'm slightly concerned about the dependency. Not that I doubt its
correctness, but because it could mean that PCI_TEGRA is not visible in
the default configuration. The only reason why it is currently visible
is because PCI_MSI is selected by some symbols that also happen to be
enabled. However, what if at some point those symbols are disabled or
removed?

Some architectures make sure that PCI_MSI is enabled by selecting it,
but that's risky, isn't it, because PCI_MSI is user-visible and could
therefore easily lead to conflicts.

Enabling PCI_MSI in the arm64 defconfig would solve the issue and is
good enough for me. I've got a couple of changes to that defconfig in
the Tegra tree for v4.17-rc1, I can add a patch to enable PCI_MSI.

Unless there are any objections.

Thierry

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