imx-sdma: fix pagefault when channel is disabled during interrupt

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

On Tue, Feb 13, 2018 at 09:47:23AM +0100, Thierry Bultel wrote:
> Add a spinlock and a 'enabled' boolean on channel descriptor, to avoid
> using buffer descriptors in the interrupt context,
> sdma_disable_channel is called meanwhile.
> ---
>  drivers/dma/imx-sdma.c | 21 +++++++++++++++++++++
>  1 file changed, 21 insertions(+)
> 
> diff --git a/drivers/dma/imx-sdma.c b/drivers/dma/imx-sdma.c
> index d1651a5..7eab42b 100644
> --- a/drivers/dma/imx-sdma.c
> +++ b/drivers/dma/imx-sdma.c
> @@ -330,6 +330,7 @@ struct sdma_channel {
>  	unsigned int			chn_real_count;
>  	struct tasklet_struct		tasklet;
>  	struct imx_dma_data		data;
> +	unsigned int 			enabled;

description says bool but this is int?

>  };
>  
>  #define IMX_DMA_SG_LOOP		BIT(0)
> @@ -588,7 +589,13 @@ static int sdma_config_ownership(struct sdma_channel *sdmac,
>  
>  static void sdma_enable_channel(struct sdma_engine *sdma, int channel)
>  {
> +	unsigned long flags;
> +	struct sdma_channel *sdmac = &sdma->channel[channel];

Empty line here please

>  	writel(BIT(channel), sdma->regs + SDMA_H_START);
> +
> +	spin_lock_irqsave(&sdmac->lock, flags);
> +	sdmac->enabled = 1;
> +	spin_unlock_irqrestore(&sdmac->lock, flags);
>  }
>  
>  /*
> @@ -677,6 +684,15 @@ static void sdma_update_channel_loop(struct sdma_channel *sdmac)
>  	struct sdma_buffer_descriptor *bd;
>  	int error = 0;
>  	enum dma_status	old_status = sdmac->status;
> +	unsigned long flags;
> +

this empty line is bogus

> +	int enabled;

and is required here. Empty line needs to be added to a fn after defining
variables and before code statements

> +	spin_lock_irqsave(&sdmac->lock, flags);
> +	enabled = sdmac->enabled;
> +	spin_unlock_irqrestore(&sdmac->lock, flags);
> +
> +	if (!enabled)
> +		return;
>  
>  	/*
>  	 * loop mode. Iterate over descriptors, re-setup them and
> @@ -930,10 +946,15 @@ static int sdma_disable_channel(struct dma_chan *chan)
>  	struct sdma_channel *sdmac = to_sdma_chan(chan);
>  	struct sdma_engine *sdma = sdmac->sdma;
>  	int channel = sdmac->channel;
> +	unsigned long flags;
>  
>  	writel_relaxed(BIT(channel), sdma->regs + SDMA_H_STATSTOP);
>  	sdmac->status = DMA_ERROR;
>  
> +	spin_lock_irqsave(&sdmac->lock, flags);
> +	sdmac->enabled = 0;
> +	spin_unlock_irqrestore(&sdmac->lock, flags);
> +
>  	return 0;
>  }
>  
> -- 
> 2.7.4
> 
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