[pulseaudio-tickets] [Bug 84585] Issue of CPU usage with HiFiBerry driver snd_soc_hifiberry_amp with Debian Wheezy kernel 3.12.28

[bugzilla-daemon at freedesktop.org]

https://bugs.freedesktop.org/show_bug.cgi?id=84585

--- Comment #21 from Raymond <superquad.vortex2 at gmail.com> ---
https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/tree/include/linux/dmaengine.h

* @DMA_RESIDUE_GRANULARITY_SEGMENT: Residue is updated after each successfully
 *  completed segment of the transfer (For cyclic transfers this is after each
 *  period). This is typically implemented by having the hardware generate an
 *  interrupt after each transferred segment and then the drivers updates the
 *  outstanding residue by the size of the segment. Another possibility is if
 *  the hardware supports scatter-gather and the segment descriptor has a field
 *  which gets set after the segment has been completed. The driver then counts
 *  the number of segments without the flag set to compute the residue.
 * @DMA_RESIDUE_GRANULARITY_BURST: Residue is updated after each transferred
 *  burst. This is typically only supported if the hardware has a progress
 *  register of some sort (E.g. a register with the current read/write address
 *  or a register with the amount of bursts/beats/bytes that have been
 *  transferred or still need to be transferred).
 */

enum dma_residue_granularity {
    DMA_RESIDUE_GRANULARITY_DESCRIPTOR = 0,
    DMA_RESIDUE_GRANULARITY_SEGMENT = 1,
    DMA_RESIDUE_GRANULARITY_BURST = 2,



timer scheduling require at least two hardware feature

DMA_RESIDUE_GRANULARITY_BURST

and

SNDRV_PCM_INFO_NO_PERIOD_WAKEUP

https://git.kernel.org/cgit/linux/kernel/git/tiwai/sound.git/log/?qt=grep&q=period+wakeup

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