linux-kernel - Re: [PATCH v2] dmaengine: qcom_hidma: Remove useless DMA-32 fallback configuration

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Date:   Sat, 19 Mar 2022 07:24:58 +0100
From:   Christophe JAILLET <christophe.jaillet@...adoo.fr>
To:     Sinan Kaya <okaya@...nel.org>, Andy Gross <agross@...nel.org>,
        Bjorn Andersson <bjorn.andersson@...aro.org>,
        Vinod Koul <vkoul@...nel.org>
Cc:     linux-kernel@...r.kernel.org, kernel-janitors@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-arm-msm@...r.kernel.org, dmaengine@...r.kernel.org
Subject: Re: [PATCH v2] dmaengine: qcom_hidma: Remove useless DMA-32 fallback
 configuration

Le 22/01/2022 à 19:05, Sinan Kaya a écrit :
> On 1/15/2022 2:35 AM, Christophe JAILLET wrote:
>> As stated in [1], dma_set_mask() with a 64-bit mask never fails if
>> dev->dma_mask is non-NULL.
>> So, if it fails, the 32 bits case will also fail for the same reason.
>>
>> Simplify code and remove some dead code accordingly.
>>
>> [1]: 
>> https://lore.kernel.org/linux-kernel/YL3vSPK5DXTNvgdx@infradead.org/#t
>>
> 
> Can we please document this?

Hi, the patch has been applied, but [1] is sometimes given as an 
explanation link.

CJ


[1]: 
https://lists.linuxfoundation.org/pipermail/iommu/2019-February/033674.html

> 
> Usual practice was to try allocating 64 bit DMA if possible and fallback
> to 32 bits.
> 
>> Signed-off-by: Christophe JAILLET <christophe.jaillet@...adoo.fr>
>> ---
>> v2: have the subject and updated driver match
>> ---
>>   drivers/dma/qcom/hidma.c | 4 +---
>>   1 file changed, 1 insertion(+), 3 deletions(-)
>>
>> diff --git a/drivers/dma/qcom/hidma.c b/drivers/dma/qcom/hidma.c
>> index 65d054bb11aa..51587cf8196b 100644
>> --- a/drivers/dma/qcom/hidma.c
>> +++ b/drivers/dma/qcom/hidma.c
>> @@ -838,9 +838,7 @@ static int hidma_probe(struct platform_device *pdev)
>>       rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(64));
>>       if (rc) {
>>           dev_warn(&pdev->dev, "unable to set coherent mask to 64");
>> -        rc = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(32));
>> -        if (rc)
>> -            goto dmafree;
>> +        goto dmafree;
>>       }
>>       dmadev->lldev = hidma_ll_init(dmadev->ddev.dev,
> 
>