linux-kernel - Re: [PATCH 2/3] dma-mapping: don't return errors from dma_set_seg

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Message-ID: <5895603b-945f-4b05-991c-76b590094354@samsung.com>
Date: Thu, 1 Aug 2024 14:00:56 +0200
From: Marek Szyprowski <m.szyprowski@...sung.com>
To: Christoph Hellwig <hch@....de>, Robin Murphy <robin.murphy@....com>
Cc: iommu@...ts.linux.dev, linux-kernel@...r.kernel.org
Subject: Re: [PATCH 2/3] dma-mapping: don't return errors from
 dma_set_seg_boundary

On 23.07.2024 02:05, Christoph Hellwig wrote:
> If dev->dma_parms is not allocate that indicates a grave bug in the
> implementation of a DMA-capable bus.  There isn't much the driver can
> do in terms of error handling, so just warn and continue as DMA
> operations will fail anyway.
>
> Signed-off-by: Christoph Hellwig <hch@....de>

What about devices on platform or usb bus and subsystems calling this 
unconditionally, like scsi_init_limits()? With today's linux-next I got 
a bunch of warnings from this call for various USB storage devices. 
Before this patch, the errors from dma_set_seg_boundary() were silently 
ignored.

> ---
>   include/linux/dma-mapping.h | 10 ++++------
>   1 file changed, 4 insertions(+), 6 deletions(-)
>
> diff --git a/include/linux/dma-mapping.h b/include/linux/dma-mapping.h
> index cfd6bafec3f944..6bd1333dbacb9b 100644
> --- a/include/linux/dma-mapping.h
> +++ b/include/linux/dma-mapping.h
> @@ -559,13 +559,11 @@ static inline unsigned long dma_get_seg_boundary_nr_pages(struct device *dev,
>   	return (dma_get_seg_boundary(dev) >> page_shift) + 1;
>   }
>   
> -static inline int dma_set_seg_boundary(struct device *dev, unsigned long mask)
> +static inline void dma_set_seg_boundary(struct device *dev, unsigned long mask)
>   {
> -	if (dev->dma_parms) {
> -		dev->dma_parms->segment_boundary_mask = mask;
> -		return 0;
> -	}
> -	return -EIO;
> +	if (WARN_ON_ONCE(!dev->dma_parms))
> +		return;
> +	dev->dma_parms->segment_boundary_mask = mask;
>   }
>   
>   static inline unsigned int dma_get_min_align_mask(struct device *dev)

Best regards
-- 
Marek Szyprowski, PhD
Samsung R&D Institute Poland