linux-kernel - Re: [PATCH] dmaengine: mmp_pdma: fix DMA mask handling

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Message-ID: <CA+G9fYsTz6WTetGeWn=NX0fyX_j6qRR9XA_ETmJiYWDfCwyHWg@mail.gmail.com>
Date: Mon, 6 Oct 2025 18:11:00 +0530
From: Naresh Kamboju <naresh.kamboju@...aro.org>
To: Guodong Xu <guodong@...cstar.com>
Cc: Vinod Koul <vkoul@...nel.org>, Nathan Chancellor <nathan@...nel.org>, 
	Nick Desaulniers <nick.desaulniers+lkml@...il.com>, Bill Wendling <morbo@...gle.com>, 
	Justin Stitt <justinstitt@...gle.com>, Yixun Lan <dlan@...too.org>, dmaengine@...r.kernel.org, 
	linux-kernel@...r.kernel.org, llvm@...ts.linux.dev, 
	linux-riscv@...ts.infradead.org, spacemit@...ts.linux.dev, elder@...cstar.com, 
	Arnd Bergmann <arnd@...db.de>
Subject: Re: [PATCH] dmaengine: mmp_pdma: fix DMA mask handling

On Thu, 18 Sept 2025 at 19:57, Guodong Xu <guodong@...cstar.com> 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@...aro.org>
> Closes: https://lore.kernel.org/lkml/CA+G9fYsPcMfW-e_0_TRqu4cnwqOqYF3aJOeKUYk6Z4qRStdFvg@mail.gmail.com
> Suggested-by: Arnd Bergmann <arnd@...db.de>
> Signed-off-by: Guodong Xu <guodong@...cstar.com>

Patch applied on top of Linux next-20251003 tag and build test pass.

Tested-by: Naresh Kamboju <naresh.kamboju@...aro.org>

- Naresh