On Tue, Feb 11, 2025 at 11:00:19PM +0100, Janne Grunau wrote: > On Tue, Feb 11, 2025 at 08:56:04PM +0100, Janne Grunau wrote: > > On Tue, Feb 11, 2025 at 12:38:59PM -0600, Bjorn Helgaas wrote: > > > On Tue, Feb 11, 2025 at 01:03:52PM -0500, Alyssa Rosenzweig wrote: > > > > From: Janne Grunau <j@xxxxxxxxxx> > > > > > > > > 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? > > > > I don't remember and it might have changed in the meantime due to iommu > > subsystem changes. What currently happens is that > > apple_dart_attach_dev_identity() fails with -EINVAL. I can't say whether > > that results in a failure to probe now. I'll test and report back. > > Using a kernel with 4K page size It results now in following warning per > PCI device: > > | ------------[ cut here ]------------ > | WARNING: CPU: 7 PID: 260 at drivers/iommu/iommu.c:2979 iommu_setup_default_domain+0x348/0x590 This should be added to the patch description. - Mani -- மணிவண்ணன் சதாசிவம்
