Re: [PATCH v16 5/7] spi: pxa2xx: disable DMA for Apple MacBook8,1

Mark Brown <[email protected]> Tue, 21 Jul 2026 16:05:52 +0100

Newsgroups	org.kernel.vger.linux-spi,org.infradead.lists.linux-arm-kernel,org.kernel.vger.linux-kernel
Message-ID	<[email protected]>

On Tue, Jul 21, 2026 at 10:34:20PM +0800, Shih-Yuan Lee (FourDollars) wrote:
> On Tue, Jul 21, 2026 at 5:26 PM Shih-Yuan Lee (FourDollars)
> > On Tue, Jul 21, 2026 at 5:18 PM Lukas Wunner <[email protected]> wrote:

> > > It would seem better to fix up the incorrect interrupt number in a quirk,
> > > rather than disabling DMA wholesale.

> > I appreciate the comment. Based on the Bugzilla feedback regarding the
> > incorrect interrupt assignment, it seems fixing the IRQ value via a
> > quirk is indeed a better approach than disabling DMA wholesale. While
> > I am not certain this will resolve the issue entirely, it looks very
> > promising. I will investigate the IRQ mis-assignment problem further.

> 1. DMAR/IOMMU Validation Failure (Error -22)
> On modern kernels with Interrupt Remapping (DMAR) enabled, overriding
> pdev->irq to 21 causes the dw_dmac_pci driver probe to fail with
> -EINVAL (-22) during request_irq(). This is because the
> DMAR/IOMMU strictly validates the PCI Requester ID (source ID) against
> the GSI mapping defined in the ACPI _PRT table. Forcing a device
> mapped to GSI 20 (00:15.0) to register on GSI 21 triggers a
> source ID mismatch check, which the kernel rejects.

That really seems like something we ought to be able to do, though I
think the idiom here is to patch the ACPI tables so they are correct
rather than quirk things in C code.  ICBW about the preferred approach
there.

BTW, if you're using a LLM to assist with analysis please don't just
paste the output into mail.  Instead make sure you understand what the
LLM is saying and write up the salient bits.

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