Subject: Re: [REGRESSION] Recent swiotlb DMA_FROM_DEVICE fixes break ath9k-based AP

From: Oleksandr Natalenko <[email-masked]>
Date: Thu, 24 Mar 2022 11:25:06 +0100

Hello.

On čtvrtek 24. března 2022 6:57:32 CET Christoph Hellwig wrote:
> On Wed, Mar 23, 2022 at 08:54:08PM +0000, Robin Murphy wrote:
> > I'll admit I still never quite grasped the reason for also adding the 
> > override to swiotlb_sync_single_for_device() in aa6f8dcbab47, but I think 
> > by that point we were increasingly tired and confused and starting to 
> > second-guess ourselves (well, I was, at least). I don't think it's wrong 
> > per se, but as I said I do think it can bite anyone who's been doing 
> > dma_sync_*() wrong but getting away with it until now. If ddbd89deb7d3 
> > alone turns out to work OK then I'd be inclined to try a partial revert of 
> > just that one hunk.
> 
> Agreed.  Let's try that first.
> 
> Oleksandr, can you try the patch below:
> 
> 
> diff --git a/kernel/dma/swiotlb.c b/kernel/dma/swiotlb.c
> index 6db1c475ec827..6c350555e5a1c 100644
> --- a/kernel/dma/swiotlb.c
> +++ b/kernel/dma/swiotlb.c
> @@ -701,13 +701,10 @@ void swiotlb_tbl_unmap_single(struct device *dev, phys_addr_t tlb_addr,
>  void swiotlb_sync_single_for_device(struct device *dev, phys_addr_t tlb_addr,
>  		size_t size, enum dma_data_direction dir)
>  {
> -	/*
> -	 * Unconditional bounce is necessary to avoid corruption on
> -	 * sync_*_for_cpu or dma_ummap_* when the device didn't overwrite
> -	 * the whole lengt of the bounce buffer.
> -	 */
> -	swiotlb_bounce(dev, tlb_addr, size, DMA_TO_DEVICE);
> -	BUG_ON(!valid_dma_direction(dir));
> +	if (dir == DMA_TO_DEVICE || dir == DMA_BIDIRECTIONAL)
> +		swiotlb_bounce(dev, tlb_addr, size, DMA_TO_DEVICE);
> +	else
> +		BUG_ON(dir != DMA_FROM_DEVICE);
>  }
>  
>  void swiotlb_sync_single_for_cpu(struct device *dev, phys_addr_t tlb_addr,
> 

With this patch the AP works for me.

Thanks.

-- 
Oleksandr Natalenko (post-factum)