linux-kernel - Re: [PATCH 4/7] dmaengine: at_xdmac: adapt perid for mem2mem operations

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Date:   Wed, 23 Sep 2020 05:30:40 +0000
From:   <Tudor.Ambarus@...rochip.com>
To:     <Eugen.Hristev@...rochip.com>, <vkoul@...nel.org>,
        <robh+dt@...nel.org>, <Ludovic.Desroches@...rochip.com>
CC:     <dmaengine@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-arm-kernel@...ts.infradead.org>,
        <linux-kernel@...r.kernel.org>, <Nicolas.Ferre@...rochip.com>
Subject: Re: [PATCH 4/7] dmaengine: at_xdmac: adapt perid for mem2mem
 operations

On 9/14/20 5:09 PM, Eugen Hristev wrote:
> The PERID in the CC register for mem2mem operations must match an unused
> PERID.
> The PERID field is 7 bits, but the selected value is 0x3f.
> On later products we can have more reserved PERIDs for actual peripherals,
> thus this needs to be increased to maximum size.
> Changing the value to 0x7f, which is the maximum for 7 bits field.
> 

Maybe it is worth to explain that for memory-to-memory transfers, PERID
should be set to an unused peripheral ID, and the maximum value seems the
safest. Anyway with or without this addressed, one can add:

Reviewed-by: Tudor Ambarus <tudor.ambarus@...rochip.com>

> Signed-off-by: Eugen Hristev <eugen.hristev@...rochip.com>
> ---
>  drivers/dma/at_xdmac.c | 6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/dma/at_xdmac.c b/drivers/dma/at_xdmac.c
> index fab19e00a7be..81bb90206092 100644
> --- a/drivers/dma/at_xdmac.c
> +++ b/drivers/dma/at_xdmac.c
> @@ -726,7 +726,7 @@ at_xdmac_interleaved_queue_desc(struct dma_chan *chan,
>  	 * match the one of another channel. If not, it could lead to spurious
>  	 * flag status.
>  	 */
> -	u32			chan_cc = AT_XDMAC_CC_PERID(0x3f)
> +	u32			chan_cc = AT_XDMAC_CC_PERID(0x7f)
>  					| AT_XDMAC_CC_DIF(0)
>  					| AT_XDMAC_CC_SIF(0)
>  					| AT_XDMAC_CC_MBSIZE_SIXTEEN
> @@ -908,7 +908,7 @@ at_xdmac_prep_dma_memcpy(struct dma_chan *chan, dma_addr_t dest, dma_addr_t src,
>  	 * match the one of another channel. If not, it could lead to spurious
>  	 * flag status.
>  	 */
> -	u32			chan_cc = AT_XDMAC_CC_PERID(0x3f)
> +	u32			chan_cc = AT_XDMAC_CC_PERID(0x7f)
>  					| AT_XDMAC_CC_DAM_INCREMENTED_AM
>  					| AT_XDMAC_CC_SAM_INCREMENTED_AM
>  					| AT_XDMAC_CC_DIF(0)
> @@ -1014,7 +1014,7 @@ static struct at_xdmac_desc *at_xdmac_memset_create_desc(struct dma_chan *chan,
>  	 * match the one of another channel. If not, it could lead to spurious
>  	 * flag status.
>  	 */
> -	u32			chan_cc = AT_XDMAC_CC_PERID(0x3f)
> +	u32			chan_cc = AT_XDMAC_CC_PERID(0x7f)
>  					| AT_XDMAC_CC_DAM_UBS_AM
>  					| AT_XDMAC_CC_SAM_INCREMENTED_AM
>  					| AT_XDMAC_CC_DIF(0)
>