linux-kernel - Re: [PATCH] iommu/ipmmu-vmsa: Check for error num after setting mask

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Message-ID: <c95e5d3a-d2b4-dcc1-b6ba-2e4e9ebc5bb0@arm.com>
Date:   Mon, 14 Feb 2022 12:32:21 +0000
From:   Robin Murphy <robin.murphy@....com>
To:     Joerg Roedel <joro@...tes.org>,
        Jiasheng Jiang <jiasheng@...as.ac.cn>
Cc:     will@...nel.org, iommu@...ts.linux-foundation.org,
        linux-kernel@...r.kernel.org,
        Nikita Yushchenko <nikita.yoush@...entembedded.com>,
        Laurent Pinchart <laurent.pinchart+renesas@...asonboard.com>
Subject: Re: [PATCH] iommu/ipmmu-vmsa: Check for error num after setting mask

On 2022-02-14 11:43, Joerg Roedel wrote:
> Adding more potential reviewers.
> 
> On Thu, Jan 06, 2022 at 10:43:02AM +0800, Jiasheng Jiang wrote:
>> Because of the possible failure of the dma_supported(), the
>> dma_set_mask_and_coherent() may return error num.
>> Therefore, it should be better to check it and return the error if
>> fails.

In this particular case it cannot fail on any system the driver actually 
runs on - it's a platform device so the dma_mask pointer is always 
initialised, then dma_direct_supported() on arm64 will always return 
true for any mask wider than 32 bits, while arm_dma_supported() will 
also always pass since a 32-bit system cannot have memory above 40 bits 
either.

There's no great harm in adding the check for the sake of consistency, I 
guess, but it's purely cosmetic and not fixing anything.

Thanks,
Robin.

>> Fixes: 1c894225bf5b ("iommu/ipmmu-vmsa: IPMMU device is 40-bit bus master")
>> Signed-off-by: Jiasheng Jiang <jiasheng@...as.ac.cn>
>> ---
>>   drivers/iommu/ipmmu-vmsa.c | 4 +++-
>>   1 file changed, 3 insertions(+), 1 deletion(-)
>>
>> diff --git a/drivers/iommu/ipmmu-vmsa.c b/drivers/iommu/ipmmu-vmsa.c
>> index aaa6a4d59057..7df5da44a004 100644
>> --- a/drivers/iommu/ipmmu-vmsa.c
>> +++ b/drivers/iommu/ipmmu-vmsa.c
>> @@ -1003,7 +1003,9 @@ static int ipmmu_probe(struct platform_device *pdev)
>>   	bitmap_zero(mmu->ctx, IPMMU_CTX_MAX);
>>   	mmu->features = of_device_get_match_data(&pdev->dev);
>>   	memset(mmu->utlb_ctx, IPMMU_CTX_INVALID, mmu->features->num_utlbs);
>> -	dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(40));
>> +	ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(40));
>> +	if (ret)
>> +		return ret;
>>   
>>   	/* Map I/O memory and request IRQ. */
>>   	res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
>> -- 
>> 2.25.1