Re: [PATCH v2] pwm: th1520: Fix 32-bit build with COMPILE_TEST - Uwe Kleine-König

From: "Uwe Kleine-König" <ukleinek@kernel.org>
To: FUJITA Tomonori <tomo@flapping.org>
Cc: fustini@kernel.org, guoren@kernel.org, wefu@redhat.com,
	 a.hindborg@kernel.org, acourbot@nvidia.com,
	aliceryhl@google.com,  bjorn3_gh@protonmail.com,
	boqun@kernel.org, dakr@kernel.org, daniel.almeida@collabora.com,
	 gary@garyguo.net, linux-riscv@lists.infradead.org,
	lossin@kernel.org,  m.wilczynski@samsung.com, ojeda@kernel.org,
	tamird@kernel.org, tmgross@umich.edu,  work@onurozkan.dev,
	linux-pwm@vger.kernel.org, rust-for-linux@vger.kernel.org,
	 FUJITA Tomonori <fujita.tomonori@gmail.com>,
	stable@vger.kernel.org
Subject: Re: [PATCH v2] pwm: th1520: Fix 32-bit build with COMPILE_TEST
Date: Wed, 30 Sep 2026 13:57:31 +0200	[thread overview]
Message-ID: <arz487DLBlaBrWLN@monoceros> (raw)
In-Reply-To: <20260930101257.1649945-1-tomo@flapping.org>

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On Wed, Sep 30, 2026 at 07:12:57PM +0900, FUJITA Tomonori wrote:
> From: FUJITA Tomonori <fujita.tomonori@gmail.com>
> 
> Fix the following build error on 32-bit ARM with COMPILE_TEST:
> 
>   ERROR: modpost: drivers/pwm/pwm_th1520.ko: symbol '__aeabi_uldivmod' undefined!
> 
> The driver divides u64 values when it converts between nanoseconds and
> clock cycles. On 32-bit ARM, these divisions are compiled to calls to
> __aeabi_uldivmod, which the kernel does not provide.
> 
> The TH1520 is a 64-bit RISC-V SoC, so the driver is only used on
> 64-bit kernels. There is no point in compile testing it on 32-bit.
> Limit COMPILE_TEST to 64BIT instead of changing the arithmetic to use
> the div64 helpers.
> 
> Fixes: 3c180003dffb ("pwm: th1520: Fix missing Kconfig dependencies")
> Cc: stable@vger.kernel.org
> Reported-by: Andreas Hindborg <a.hindborg@kernel.org>
> Closes: https://rust-for-linux.zulipchat.com/#narrow/channel/291565-Help/topic/64bit.20division.20in.20.60pwm_th1520.2Ers.60/near/626825599
> Reviewed-by: Andreas Hindborg <a.hindborg@kernel.org>
> Reviewed-by: Gary Guo <gary@garyguo.net>
> Signed-off-by: FUJITA Tomonori <fujita.tomonori@gmail.com>
> ---
> v2:
> - Fix a typo in the commit message
> - Add Cc: stable, Reported-by and Closes tags
> - Add Reviewed-by tags from Andreas and Gary
> - Rebase on v7.3-rc5
> 
> v1: https://lore.kernel.org/all/20260929095612.1072417-1-tomo@flapping.org/
> ---
>  drivers/pwm/Kconfig | 2 +-
>  1 file changed, 1 insertion(+), 1 deletion(-)
> 
> diff --git a/drivers/pwm/Kconfig b/drivers/pwm/Kconfig
> index 729776086879..abecd95b0c3c 100644
> --- a/drivers/pwm/Kconfig
> +++ b/drivers/pwm/Kconfig
> @@ -772,7 +772,7 @@ config PWM_TEGRA
>  
>  config PWM_TH1520
>  	tristate "TH1520 PWM support"
> -	depends on ARCH_THEAD || COMPILE_TEST
> +	depends on ARCH_THEAD || (COMPILE_TEST && 64BIT)
>  	depends on RUST
>  	depends on HAS_IOMEM && COMMON_CLK
>  	select RUST_PWM_ABSTRACTIONS

Can't we do better than that? For C code the right thing to do is to use
one of the div helpers instead of a plain / for types bigger than long.

Best regards
Uwe

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