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

From: "Arnd Bergmann" <arnd@arndb.de>
To: "Guodong Xu" <guodong@riscstar.com>,
	"Vinod Koul" <vkoul@kernel.org>,
	"Nathan Chancellor" <nathan@kernel.org>,
	"Nick Desaulniers" <nick.desaulniers+lkml@gmail.com>,
	"Bill Wendling" <morbo@google.com>,
	"Justin Stitt" <justinstitt@google.com>,
	"Yixun Lan" <dlan@gentoo.org>
Cc: dmaengine@vger.kernel.org, linux-kernel@vger.kernel.org,
	llvm@lists.linux.dev, linux-riscv@lists.infradead.org,
	spacemit@lists.linux.dev, elder@riscstar.com,
	"Naresh Kamboju" <naresh.kamboju@linaro.org>
Subject: Re: [PATCH] dmaengine: mmp_pdma: fix DMA mask handling
Date: Thu, 18 Sep 2025 18:20:07 +0200	[thread overview]
Message-ID: <d2a99673-cc0e-4024-bc66-76d395ea4313@app.fastmail.com> (raw)
In-Reply-To: <20250918-mmp-pdma-simplify-dma-addressing-v1-1-5c2be2b85696@riscstar.com>

On Thu, Sep 18, 2025, at 16:27, 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>

Reviewed-by: Arnd Bergmann <arnd@arndb.de>

Thanks for fixing this!

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