We can get audio errors if hitting deeper idle states on omaps: [alsa.c:230] error: Fatal problem with alsa output, error -5. [audio.c:614] error: Error in writing audio (Input/output error?)! This seems to happen with off mode idle enabled as power for the whole SoC may get cut off between filling the McBSP fifo using DMA. While active DMA blocks deeper idle states in hardware, McBSP activity does not seem to do so. Basing the QoS latency on the FIFO size with the approximate delay required being 2.3 milliseconds per buffer location. Note that this is different from snd_pcm_hw_constraint_step() as that can configure things based on the buffer and period size. However, that does not help to block idle between the fifo fills. Note that in theory some omaps are capable of playing audio while hitting deeper idle states. If somebody needs that and gets it working, we can set the latency requirements accordingly. Based on the original patch by Tony Lindgren Link: https://patchwork.kernel.org/patch/9305867/ Cc: Tony Lindgren <tony@xxxxxxxxxxx> Cc: Peter Ujfalusi <peter.ujfalusi@xxxxxx> Signed-off-by: Matt Ranostay <matt@ranostay.consulting> --- Changes from v1: * add calculations for latency per number of FIFO locations sound/soc/omap/mcbsp.c | 15 +++++++++++++++ 1 file changed, 15 insertions(+) diff --git a/sound/soc/omap/mcbsp.c b/sound/soc/omap/mcbsp.c index 06fec5699cc8..b4a773ca2bac 100644 --- a/sound/soc/omap/mcbsp.c +++ b/sound/soc/omap/mcbsp.c @@ -25,6 +25,7 @@ #include <linux/io.h> #include <linux/slab.h> #include <linux/pm_runtime.h> +#include <linux/pm_qos.h> #include <linux/platform_data/asoc-ti-mcbsp.h> @@ -637,12 +638,21 @@ void omap_mcbsp_free(struct omap_mcbsp *mcbsp) * Here we start the McBSP, by enabling transmitter, receiver or both. * If no transmitter or receiver is active prior calling, then sample-rate * generator and frame sync are started. + * + * Also setting of the QoS latency for the FIFO which varies upon the buffer + * size. Approximately 2.3 milliseconds per FIFO location. */ void omap_mcbsp_start(struct omap_mcbsp *mcbsp, int tx, int rx) { int enable_srg = 0; + int latency = mcbsp->pdata->buffer_size * 23; u16 w; + /* Prevent omap hardware from hitting off between fifo fills */ + if (latency) + pm_qos_add_request(&mcbsp->pm_qos_req, + PM_QOS_CPU_DMA_LATENCY, latency); + if (mcbsp->st_data) omap_st_start(mcbsp); @@ -731,6 +741,8 @@ void omap_mcbsp_stop(struct omap_mcbsp *mcbsp, int tx, int rx) if (mcbsp->st_data) omap_st_stop(mcbsp); + + pm_qos_remove_request(&mcbsp->pm_qos_req); } int omap2_mcbsp_set_clks_src(struct omap_mcbsp *mcbsp, u8 fck_src_id) @@ -1098,6 +1110,9 @@ int omap_mcbsp_init(struct platform_device *pdev) void omap_mcbsp_cleanup(struct omap_mcbsp *mcbsp) { + if (pm_qos_request_active(&mcbsp->pm_qos_req)) + pm_qos_remove_request(&mcbsp->pm_qos_req); + if (mcbsp->pdata->buffer_size) sysfs_remove_group(&mcbsp->dev->kobj, &additional_attr_group); -- 2.7.4 -- To unsubscribe from this list: send the line "unsubscribe linux-omap" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
