Re: [PATCH v4 6/8] dmaengine: dw-edma: Don't rely on the deprecated "direction" member

[Serge Semin <fancer.lancer@gmail.com>]

On Wed, Mar 09, 2022 at 03:12:02PM -0600, Frank Li wrote:
> From: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> 
> The "direction" member of the "dma_slave_config" structure is deprecated.
> The clients no longer use this field to specify the direction of the slave
> channel. But in the eDMA core, this field is used to differentiate between the
> Root complex (remote) and Endpoint (local) DMA accesses.
> 
> Nevertheless, we can't differentiate between local and remote accesses without
> a dedicated flag. So let's get rid of the old check and add a new check for
> verifying the DMA operation between local and remote memory instead.
> 
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> Signed-off-by: Frank Li <Frank.Li@nxp.com>
> ---
> no chang between v1 to v4
>  drivers/dma/dw-edma/dw-edma-core.c | 17 ++---------------
>  1 file changed, 2 insertions(+), 15 deletions(-)
> 
> diff --git a/drivers/dma/dw-edma/dw-edma-core.c b/drivers/dma/dw-edma/dw-edma-core.c
> index 507f08db1aad3..47c6a52929fcd 100644
> --- a/drivers/dma/dw-edma/dw-edma-core.c
> +++ b/drivers/dma/dw-edma/dw-edma-core.c
> @@ -341,22 +341,9 @@ dw_edma_device_transfer(struct dw_edma_transfer *xfer)
>  	if (!chan->configured)
>  		return NULL;
>  
> -	switch (chan->config.direction) {
> -	case DMA_DEV_TO_MEM: /* local DMA */
> -		if (dir == DMA_DEV_TO_MEM && chan->dir == EDMA_DIR_READ)
> -			break;
> -		return NULL;
> -	case DMA_MEM_TO_DEV: /* local DMA */
> -		if (dir == DMA_MEM_TO_DEV && chan->dir == EDMA_DIR_WRITE)
> -			break;

> +	/* eDMA supports only read and write between local and remote memory */

The comment is a bit confusing because both cases are named as
"memory" while the permitted directions contains DEV-part, which
means "device". What I would suggest to write here is something like:
"DW eDMA supports transferring data from/to the CPU/Application memory
to/from the PCIe link partner device by injecting the PCIe MWr/MRd TLPs."

-Sergey

> +	if (dir != DMA_DEV_TO_MEM && dir != DMA_MEM_TO_DEV)
>  		return NULL;
> -	default: /* remote DMA */
> -		if (dir == DMA_MEM_TO_DEV && chan->dir == EDMA_DIR_READ)
> -			break;
> -		if (dir == DMA_DEV_TO_MEM && chan->dir == EDMA_DIR_WRITE)
> -			break;
> -		return NULL;
> -	}
>  
>  	if (xfer->type == EDMA_XFER_CYCLIC) {
>  		if (!xfer->xfer.cyclic.len || !xfer->xfer.cyclic.cnt)
> -- 
> 2.24.0.rc1
>