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

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Message-ID: <ee43d68f-000c-6513-38f2-877b9018ab22@kernel.org>
Date:   Sat, 22 Jan 2022 13:05:30 -0500
From:   Sinan Kaya <okaya@...nel.org>
To:     Christophe JAILLET <christophe.jaillet@...adoo.fr>,
        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

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?

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,