linux-kernel - Re: [PATCH] PCI: apple: Add depends on PAGE_SIZE

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Message-ID: <20250211183859.GA51030@bhelgaas>
Date: Tue, 11 Feb 2025 12:38:59 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Alyssa Rosenzweig <alyssa@...enzweig.io>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	linux-pci@...r.kernel.org, linux-kernel@...r.kernel.org,
	Janne Grunau <j@...nau.net>
Subject: Re: [PATCH] PCI: apple: Add depends on PAGE_SIZE_16KB

On Tue, Feb 11, 2025 at 01:03:52PM -0500, Alyssa Rosenzweig wrote:
> From: Janne Grunau <j@...nau.net>
> 
> The iommu on Apple's M1 and M2 supports only a page size of 16kB and is
> mandatory for PCIe devices. Mismatched page sizes will render devices
> useless due to non-working DMA. While the iommu prints a warning in this
> scenario, it seems a common and hard to debug problem, so prevent it at
> build-time.

Can we include a sample iommu warning here to help people debug this
problem?

> Signed-off-by: Janne Grunau <j@...nau.net>
> Signed-off-by: Alyssa Rosenzweig <alyssa@...enzweig.io>
> ---
>  drivers/pci/controller/Kconfig | 1 +
>  1 file changed, 1 insertion(+)
> 
> diff --git a/drivers/pci/controller/Kconfig b/drivers/pci/controller/Kconfig
> index 9800b768105402d6dd1ba4b134c2ec23da6e4201..507e6ac5d65257578e4eec74b459f6605c9c2907 100644
> --- a/drivers/pci/controller/Kconfig
> +++ b/drivers/pci/controller/Kconfig
> @@ -39,6 +39,7 @@ config PCIE_APPLE
>  	depends on ARCH_APPLE || COMPILE_TEST
>  	depends on OF
>  	depends on PCI_MSI
> +	depends on PAGE_SIZE_16KB || COMPILE_TEST
>  	select PCI_HOST_COMMON
>  	help
>  	  Say Y here if you want to enable PCIe controller support on Apple
> 
> ---
> base-commit: 2014c95afecee3e76ca4a56956a936e23283f05b
> change-id: 20250211-pci-16k-4c391a5dcd18
> 
> Best regards,
> -- 
> Alyssa Rosenzweig <alyssa@...enzweig.io>
>