Re: [PATCH] Staging: comedi: Add DMA preparation before mite_dma_arm().

[Ian Abbott]

On 2025-04-03 17:35, Wentao Liang wrote:
> The ni_tio_input_inttrig() calls mite_dma_arm() without calling
> mite_prep_dma() first. A proper implementation can be found in
> ni_cdo_inttrig() in ni_mio_common.c.
>
> Add mite_prep_dma() before mite_dma_arm().
>
> Fixes: cb7859a90af1 ("Staging: comedi: add National Instruments infrastructure")
> Signed-off-by: Wentao Liang <vulab@xxxxxxxxxxx>
> ---
>   drivers/comedi/drivers/ni_tiocmd.c | 5 +++--
>   1 file changed, 3 insertions(+), 2 deletions(-)
>
> diff --git a/drivers/comedi/drivers/ni_tiocmd.c b/drivers/comedi/drivers/ni_tiocmd.c
> index ab6d9e8269f3..b943836ccf1a 100644
> --- a/drivers/comedi/drivers/ni_tiocmd.c
> +++ b/drivers/comedi/drivers/ni_tiocmd.c
> @@ -84,9 +84,10 @@ static int ni_tio_input_inttrig(struct comedi_device *dev,
>   		return -EINVAL;
>   
>   	spin_lock_irqsave(&counter->lock, flags);
> -	if (counter->mite_chan)
> +	if (counter->mite_chan) {
> +		mite_prep_dma(counter->mite_chan, 32, 32);
>   		mite_dma_arm(counter->mite_chan);
> -	else
> +	} else
>   		ret = -EIO;
>   	spin_unlock_irqrestore(&counter->lock, flags);
>   	if (ret < 0)

mite_prep_dma() will get called by ni_tio_input_cmd() at some arbitrary 
time before ni_tio_input_inttrig() is called. (ni_tio_input_cmd() sets 
up the software trigger function pointer that is called during 
processing of a subsequent INSN_INTTRIG comedi instruction from 
user-space. Also, the last two parameters of mite_prep_dma() are not 
always 32 and 32 - it depends on the hardware, as can be seen in the 
switch statement in ni_tio_input_cmd().

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