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

On Tue, Jul 21, 2026 at 10:49:17PM +0800, Shih-Yuan Lee (FourDollars) wrote:
> On Tue, Jul 21, 2026 at 3:27 AM Andy Shevchenko
> <[email protected]> wrote:
> > On Tue, Jul 21, 2026 at 12:21:14AM +0800, Shih-Yuan Lee wrote:

...

> Thank you for the review and feedback.
> 
> Regarding your question about why DMA fails on this hardware, I have
> just sent a detailed reply to Lukas in this thread outlining our
> physical verification findings. In short, I confirmed that the
> DMA controller's physical interrupt line is not functioning on this
> motherboard,

It might be wrongly described in ACPI tables, but in HW it works.

> and macOS and Windows 10 also completely bypass the DMA
> controller. Please refer to that email for the DMAR/IOMMU and
> cross-OS analysis details.
> 
> Regarding your other comments:

> 2. The force_pio Module Parameter:
> The original spi-pxa2xx driver is designed to hardcode DMA usage if
> DMA channels are available. I introduced the force_pio module
> parameter for two reasons:
>   • It serves as a diagnostic tool for users on similar hardware to
> easily test and verify if their issues are related to DMA.
>   • It allows developers to easily test and debug the PIO code path on
> DMA-capable LPSS hardware to prevent regressions.
> 
> That being said, if module parameters of this type are strictly not
> preferred, I am completely fine with removing force_pio and keeping
> only the DMI-based quirk for the MacBook8,1. Please let me know your
> preference.

Neither is preferred until we will fully understand what's going on there.
Yes, DMI quirk is a last resort, but to come to that we need to try better
options. See my other reply about the DMA case.

-- 
With Best Regards,
Andy Shevchenko