Re: [PATCH] Revert "dma: use dma/cpu conversions correctly in dma_map/unmap_single"

[Ahmad Fatoum <a.fatoum@pengutronix.de>]

On 31.05.23 12:23, Sascha Hauer wrote:
> This reverts commit d13d870986eeecc58d8652268557e4a159b9d4c4.
> 
> While the patch itself is correct, it at least breaks USB on the
> Raspberry Pi 3b.
> 
> With this patch dma_sync_single_for_device() is passed the DMA address.
> This is correct as even the prototype suggests that it should get a
> dma_addr_t. Unfortunately this is not what the function implements and
> also not what the users expect. Most if not all users simply pass a CPU
> pointer casted to unsigned long. dma_sync_single_for_device() on ARM
> then takes the DMA address as a CPU pointer and does cache maintenance
> on it.
> 
> Before we can merge this patch again dma_sync_single_for_device() must
> get a struct device * argument and (on ARM) the cpu_to_dma() conversion
> must be reverted before doing cache maintenance.

@Denis, could you give some background on your patch? I assume this was
for MIPS? Did this patch fix breakage for you? In what driver? Maybe
a follow-up patch that fixes your particular breakage while not breaking
ARM could be found until that wart is cleaned up for good.

Cheers,
Ahmad


> ---
>  drivers/dma/map.c | 10 ++++++----
>  1 file changed, 6 insertions(+), 4 deletions(-)
> 
> diff --git a/drivers/dma/map.c b/drivers/dma/map.c
> index fea04c38a3..114c0f7db3 100644
> --- a/drivers/dma/map.c
> +++ b/drivers/dma/map.c
> @@ -23,15 +23,17 @@ static inline void *dma_to_cpu(struct device *dev, dma_addr_t addr)
>  dma_addr_t dma_map_single(struct device *dev, void *ptr, size_t size,
>  			  enum dma_data_direction dir)
>  {
> -	dma_addr_t ret = cpu_to_dma(dev, ptr);
> +	unsigned long addr = (unsigned long)ptr;
>  
> -	dma_sync_single_for_device(ret, size, dir);
> +	dma_sync_single_for_device(addr, size, dir);
>  
> -	return ret;
> +	return cpu_to_dma(dev, ptr);
>  }
>  
>  void dma_unmap_single(struct device *dev, dma_addr_t dma_addr, size_t size,
>  		      enum dma_data_direction dir)
>  {
> -	dma_sync_single_for_cpu(dma_addr, size, dir);
> +	unsigned long addr = (unsigned long)dma_to_cpu(dev, dma_addr);
> +
> +	dma_sync_single_for_cpu(addr, size, dir);
>  }

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