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: <5fddf99c-c0ad-4652-82d4-d5bb47fb63bd@nvidia.com>
Date: Wed, 5 Feb 2025 11:28:59 +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 11:27, Jon Hunter wrote:
> 
> 
> 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@...el.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)))

Nevermind, patch 2/2 addresses this.

Jon

-- 
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