Re: [PATCH] dmaengine: mmp_pdma: fix DMA mask handling

Nathan Chancellor
2025-10-13T17:01:01Z

Hi Vinod,

On Tue, Sep 30, 2025 at 03:10:01PM -0700, Nathan Chancellor wrote:
> On Thu, Sep 18, 2025 at 10:27:27PM +0800, Guodong Xu wrote:
> > The driver's existing logic for setting the DMA mask for "marvell,pdma-1.0"
> > was flawed. It incorrectly relied on pdev->dev->coherent_dma_mask instead
> > of declaring the hardware's fixed addressing capability. A cleaner and
> > more correct approach is to define the mask directly based on the hardware
> > limitations.
> >
> > The MMP/PXA PDMA controller is a 32-bit DMA engine. This is supported by
> > datasheets and various dtsi files for PXA25x, PXA27x, PXA3xx, and MMP2,
> > all of which are 32-bit systems.
> >
> > This patch simplifies the driver's logic by replacing the 'u64 dma_mask'
> > field with a simpler 'u32 dma_width' to store the addressing capability
> > in bits. The complex if/else block in probe() is then replaced with a
> > single, clear call to dma_set_mask_and_coherent(). This sets a fixed
> > 32-bit DMA mask for "marvell,pdma-1.0" and a 64-bit mask for
> > "spacemit,k1-pdma," matching each device's hardware capabilities.
> >
> > Finally, this change also works around a specific build error encountered
> > with clang-20 on x86_64 allyesconfig. The shift-count-overflow error is
> > caused by a known clang compiler issue where the DMA_BIT_MASK(n) macro's
> > ternary operator is not correctly evaluated in static initializers. By
> > moving the macro's evaluation into the probe() function, the driver avoids
> > this compiler bug.
> >
> > Fixes: 5cfe585d8624 ("dmaengine: mmp_pdma: Add SpacemiT K1 PDMA support with 64-bit addressing")
> > Reported-by: Naresh Kamboju <naresh.kamboju@linaro.org>
> > Closes: https://lore.kernel.org/lkml/CA+G9fYsPcMfW-e_0_TRqu4cnwqOqYF3aJOeKUYk6Z4qRStdFvg@mail.gmail.com
> > Suggested-by: Arnd Bergmann <arnd@arndb.de>
> > Signed-off-by: Guodong Xu <guodong@riscstar.com>
>
> Tested-by: Nathan Chancellor <nathan@kernel.org> # build
>
> It would be great if this could be picked up before the 6.18 DMA pull
> request so that I do not have to patch our CI to avoid this issue.

This patch resolves a (bogus) clang warning that breaks the build with
-Werror. Can you please queue this for a future DMA fixes pull request?
This has been available for almost a month and really should have made
the original 6.18 pull request but I dropped the ball on pinging again
before it went out since I was dealing with Kbuild this cycle.

Cheers,
Nathan