Re: [PATCH 1/2] dmaengine: ep93xx: Always start from BASE0

[Vinod Koul <vinod.koul@intel.com>]

On Sun, May 14, 2017 at 12:13:26AM +0200, Alexander Sverdlin wrote:
> The current buffer is being reset to zero on device_free_chan_resources()
> but not on device_terminate_all(). It could happen that HW is restarted and
> expects BASE0 to be used, but the driver is not synchronized and will start
> from BASE1. Therefore, it's better to reset the buffer explicitly in
> m2p_hw_setup(). While here, check that HW really starts from BASE0 and
> warn otherwise.
> 
> Signed-off-by: Alexander Sverdlin <alexander.sverdlin@gmail.com>
> Cc: stable@vger.kernel.org
> ---
>  drivers/dma/ep93xx_dma.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/dma/ep93xx_dma.c b/drivers/dma/ep93xx_dma.c
> index d37e8dda8079..a3d946d2a8e1 100644
> --- a/drivers/dma/ep93xx_dma.c
> +++ b/drivers/dma/ep93xx_dma.c
> @@ -45,6 +45,7 @@
>  
>  #define M2P_PPALLOC			0x0008
>  #define M2P_STATUS			0x000c
> +#define M2P_STATUS_NEXTBUFFER		BIT(6)
>  
>  #define M2P_MAXCNT0			0x0020
>  #define M2P_BASE0			0x0024
> @@ -312,6 +313,13 @@ static void m2p_set_control(struct ep93xx_dma_chan *edmac, u32 control)
>  	readl(edmac->regs + M2P_CONTROL);
>  }
>  
> +static inline u32 m2p_channel_nextbuf(struct ep93xx_dma_chan *edmac)
> +{
> +	if (readl(edmac->regs + M2P_STATUS) & M2P_STATUS_NEXTBUFFER)
> +		return 1;
> +	return 0;
> +}
> +
>  static int m2p_hw_setup(struct ep93xx_dma_chan *edmac)
>  {
>  	struct ep93xx_dma_data *data = edmac->chan.private;
> @@ -323,6 +331,10 @@ static int m2p_hw_setup(struct ep93xx_dma_chan *edmac)
>  		| M2P_CONTROL_ENABLE;
>  	m2p_set_control(edmac, control);
>  
> +	if (m2p_channel_nextbuf(edmac) != 0)
> +		dev_warn(chan2dev(edmac), "M2P: Starting from BASE1\n");

But then you are actually not restarting from BASE1 as you reset, so the
warn is wrong.. Perhaps a more meaningful msg would be to say "expected 0
but found 1, so resetting"

> +	edmac->buffer = 0;
> +
>  	return 0;
>  }
>  
> -- 
> 2.12.2
> 

-- 
~Vinod