linux-kernel - Re: [PATCH] fpga: dfl: pci: Remove useless DMA-32 fallback configuration

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Date:   Fri, 18 Mar 2022 18:34:57 +0800
From:   Xu Yilun <yilun.xu@...el.com>
To:     cgel.zte@...il.com
Cc:     hao.wu@...el.com, trix@...hat.com, linux-fpga@...r.kernel.org,
        linux-kernel@...r.kernel.org, Minghao Chi <chi.minghao@....com.cn>,
        Zeal Robot <zealci@....com.cn>
Subject: Re: [PATCH] fpga: dfl: pci: Remove useless DMA-32 fallback
 configuration

On Fri, Mar 18, 2022 at 12:59:38AM +0000, cgel.zte@...il.com wrote:
> From: Minghao Chi <chi.minghao@....com.cn>
> 
> As stated in [1], dma_set_mask() with a 64-bit mask will never fail if
> dev->dma_mask is non-NULL.
> So, if it fails, the 32 bits case will also fail for the same reason.

The code change is good to me, but maybe the commit message could be
improved. The reference [1] is not the best to make things clear, maybe
[2] could be better undstood. It is even better if there is a brief
introduction of the DMA API change in the commit message. It saves a lot
of time for reviewers.

I see there are plenty of similar places to change, could you make a
patchset and change them in a batch?

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

Thanks,
Yilun

> 
> Simplify code and remove some dead code accordingly.
> 
> [1]: https://lkml.org/lkml/2021/6/7/398
> 
> Reported-by: Zeal Robot <zealci@....com.cn>
> Signed-off-by: Minghao Chi <chi.minghao@....com.cn>
> ---
>  drivers/fpga/dfl-pci.c | 2 --
>  1 file changed, 2 deletions(-)
> 
> diff --git a/drivers/fpga/dfl-pci.c b/drivers/fpga/dfl-pci.c
> index 717ac9715970..42fdfa7a28d6 100644
> --- a/drivers/fpga/dfl-pci.c
> +++ b/drivers/fpga/dfl-pci.c
> @@ -356,8 +356,6 @@ int cci_pci_probe(struct pci_dev *pcidev, const struct pci_device_id *pcidevid)
>  	pci_set_master(pcidev);
>  
>  	ret = dma_set_mask_and_coherent(&pcidev->dev, DMA_BIT_MASK(64));
> -	if (ret)
> -		ret = dma_set_mask_and_coherent(&pcidev->dev, DMA_BIT_MASK(32));
>  	if (ret) {
>  		dev_err(&pcidev->dev, "No suitable DMA support available.\n");
>  		goto disable_error_report_exit;
> -- 
> 2.25.1