linux-kernel - Re: [PATCH v4 1/2] dmaengine: tegra210-adma: Fix build error due to 64-by-32 division

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Message-ID: <dd094508-482d-4ed6-b9b4-77607fd18f4a@nvidia.com>
Date: Wed, 5 Feb 2025 11:27:50 +0000
From: Jon Hunter <jonathanh@...dia.com>
To: Mohan Kumar D <mkumard@...dia.com>, vkoul@...nel.org,
 thierry.reding@...il.com
Cc: dmaengine@...r.kernel.org, linux-tegra@...r.kernel.org,
 linux-kernel@...r.kernel.org, stable@...r.kernel.org,
 kernel test robot <lkp@...el.com>
Subject: Re: [PATCH v4 1/2] dmaengine: tegra210-adma: Fix build error due to
 64-by-32 division



On 05/02/2025 03:31, Mohan Kumar D wrote:
> Kernel test robot reported the build errors on 32-bit platforms due to
> plain 64-by-32 division. Following build erros were reported.
> 
>     "ERROR: modpost: "__udivdi3" [drivers/dma/tegra210-adma.ko] undefined!
>      ld: drivers/dma/tegra210-adma.o: in function `tegra_adma_probe':
>      tegra210-adma.c:(.text+0x12cf): undefined reference to `__udivdi3'"
> 
> This can be fixed by using div_u64() for the adma address space
> 
> Fixes: 68811c928f88 ("dmaengine: tegra210-adma: Support channel page")
> Cc: stable@...r.kernel.org
> Reported-by: kernel test robot <lkp@...el.com>
> Closes: https://lore.kernel.org/oe-kbuild-all/202412250204.GCQhdKe3-lkp@intel.com/
> Signed-off-by: Mohan Kumar D <mkumard@...dia.com>
> ---
>   drivers/dma/tegra210-adma.c | 15 +++++++++++----
>   1 file changed, 11 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/dma/tegra210-adma.c b/drivers/dma/tegra210-adma.c
> index 6896da8ac7ef..a0bd4822ed80 100644
> --- a/drivers/dma/tegra210-adma.c
> +++ b/drivers/dma/tegra210-adma.c
> @@ -887,7 +887,8 @@ static int tegra_adma_probe(struct platform_device *pdev)
>   	const struct tegra_adma_chip_data *cdata;
>   	struct tegra_adma *tdma;
>   	struct resource *res_page, *res_base;
> -	int ret, i, page_no;
> +	u64 page_no, page_offset;
> +	int ret, i;
>   
>   	cdata = of_device_get_match_data(&pdev->dev);
>   	if (!cdata) {
> @@ -914,10 +915,16 @@ static int tegra_adma_probe(struct platform_device *pdev)
>   
>   		res_base = platform_get_resource_byname(pdev, IORESOURCE_MEM, "global");
>   		if (res_base) {
> -			page_no = (res_page->start - res_base->start) / cdata->ch_base_offset;
> -			if (page_no <= 0)
> +			if (WARN_ON(res_page->start <= res_base->start))
>   				return -EINVAL;
> -			tdma->ch_page_no = page_no - 1;
> +
> +			page_offset = res_page->start - res_base->start;
> +			page_no = div_u64(page_offset, cdata->ch_base_offset);
> +
> +			if (WARN_ON(page_no == 0))
> +				return -EINVAL;

Sorry to be pedantic but should this now be ...

if (WARN_ON((page_no == 0) || (page_no > UINT_MAX)))

Jon

> +
> +			tdma->ch_page_no = lower_32_bits(page_no) - 1;
>   			tdma->base_addr = devm_ioremap_resource(&pdev->dev, res_base);
>   			if (IS_ERR(tdma->base_addr))
>   				return PTR_ERR(tdma->base_addr);

-- 
nvpublic