At Sun, 29 Oct 2006 15:19:40 +1100,
Paul Mackerras wrote:
>
> This fixes the problem of getting extra bytes inserted at the
> beginning of a recording when using the Apple i2s interface and DBDMA
> controller. It turns out that we can't just abort the DMA; we have to
> let it stop at the end of a command, and then wait for the S7 bit to
> be set before turning off the DBDMA controller. Doing that for
> playback doesn't seem to be necessary, but doesn't hurt either.
>
> We use the technique used by the Darwin driver: make each transfer
> command branch to a stop command if the S0 status bit is set. Thus we
> can ask the DMA controller to stop at the end of the current command
> by setting S0.
>
> The interrupt routine now looks at and clears the status word of the
> DBDMA command ring. This is necessary so it can know when the DBDMA
> controller has seen that S0 is set, and so when it should look for the
> DBDMA controller being stopped and S7 being set. This also ended up
> simplifying the calculation in i2sbus_pcm_pointer.
Thanks, the patch looks good, just very minor issues.
> --- a/sound/aoa/soundbus/i2sbus/i2sbus-pcm.c
> +++ b/sound/aoa/soundbus/i2sbus/i2sbus-pcm.c
> @@ -245,18 +245,66 @@ static int i2sbus_pcm_close(struct i2sbu
> return err;
> }
>
> +static void i2sbus_wait_for_stop(struct i2sbus_dev *i2sdev,
> + struct pcm_info *pi)
> +{
> + unsigned long flags;
> + struct completion done;
> + long timeout;
> +
> + spin_lock_irqsave(&i2sdev->low_lock, flags);
We need no irqsave/irqrestore but here since the function is supposed
to be called always in schedulable situation. spin_lock_irq() should
be enough.
> static int i2sbus_hw_params(struct snd_pcm_substream *substream,
> struct snd_pcm_hw_params *params)
> {
> return snd_pcm_lib_malloc_pages(substream, params_buffer_bytes(params));
> }
>
> -static int i2sbus_hw_free(struct snd_pcm_substream *substream)
> +static inline int i2sbus_hw_free(struct snd_pcm_substream *substream, int in)
Any reason to put extra inline here? It's no time-critical funciton,
so let compiler do optimization.
BTW, shoud this go to 2.6.19 although the fix isn't so trivial, or
could wait for the next?
Takashi
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