Subject: Re: [PATCH] arm64: cache: Lower ARCH_DMA_MINALIGN to 64 (L1_CACHE_BYTES)

From: Catalin Marinas <[email-masked]>
Date: Tue, 6 Jul 2021 11:26:35 +0100

On Tue, Jul 06, 2021 at 09:26:59AM +0000, Yassine Oudjana wrote:
> In-Reply-To: <[email-masked]>
> > Reduce ARCH_DMA_MINALIGN to 64 bytes and allow the warning/taint to
> > indicate if there are machines that unknowingly rely on this.
> 
> The warning is being triggered on Qualcomm MSM8996, as well as the out-of-spec taint:

Is this booting with ACPI or DT?

> ------------[ cut here ]------------
> rtc-pm8xxx 400f000.qcom,spmi:pmic@0:rtc@6000: ARCH_DMA_MINALIGN smaller than CTR_EL0.CWG (64 < 128)
> WARNING: CPU: 0 PID: 1 at arch/arm64/mm/dma-mapping.c:45 arch_setup_dma_ops+0xf8/0x10c
[...]
> This warning is triggered with nearly every driver probe, not only rtc-pm8xxx.

I have a suspicion none of the reported devices actually do any DMA, so
in practice it should be safe but we need to figure out why
arch_setup_dma_ops() gets called.

-- 
Catalin

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