On 08/29/16 21:27, Tony Lindgren wrote:
> 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.
>
> Let's fix the issue by adding PM QoS latency requirement for McBSP.
> Based on my experiments a working latency value is somewhere
> around 35 ms with 40 ms breaking. So let's use a safer value of 30 ms.
>
> 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.
>
> Signed-off-by: Tony Lindgren <tony@xxxxxxxxxxx>
> ---
> sound/soc/omap/mcbsp.c | 10 ++++++++++
> sound/soc/omap/mcbsp.h | 2 ++
> 2 files changed, 12 insertions(+)
>
> diff --git a/sound/soc/omap/mcbsp.c b/sound/soc/omap/mcbsp.c
> --- 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>
>
> @@ -643,6 +644,10 @@ void omap_mcbsp_start(struct omap_mcbsp *mcbsp, int tx, int rx)
> int enable_srg = 0;
> u16 w;
>
> + /* Prevent omap hardware from hitting off between fifo fills */
> + pm_qos_add_request(&mcbsp->pm_qos_req, PM_QOS_CPU_DMA_LATENCY,
> + 30 * 1000);
The latency value depends on the McBSP FIFO size and the speed the DMA can
transfer the data.
OMAP3.McBSP2 have 1280 word as buffer. All other McBSP across SoCs have 128
words or no FIFO.
The DMA fill speed will depend on several factors, I guess it is faster on
OMAP4/5 then on OMAP3/2/1.
If we have McBSP w/o FIFO there is no need for the qos AFAIK.
I'm fine with the 30ms, if you have done the testing on OMAP3.McBSP2, probably
setting 30ms for McBSP with 1280 FIFO, 3ms for 128 FIFO and no qos for McBSP
w/o FIFO might be better. Or:
latency = mcbsp->pdata->buffer_size * 23; /* 29.44ms on omap3's mcbsp2 */
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 +736,8 @@ 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 +1105,9 @@ err_thres:
>
> void omap_mcbsp_cleanup(struct omap_mcbsp *mcbsp)
> {
> + if (dev_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);
>
> diff --git a/sound/soc/omap/mcbsp.h b/sound/soc/omap/mcbsp.h
> index 61e93b1..e603f33 100644
> --- a/sound/soc/omap/mcbsp.h
> +++ b/sound/soc/omap/mcbsp.h
> @@ -325,6 +325,8 @@ struct omap_mcbsp {
> unsigned int in_freq;
> int clk_div;
> int wlen;
> +
> + struct pm_qos_request pm_qos_req;
> };
>
> void omap_mcbsp_config(struct omap_mcbsp *mcbsp,
>
--
Péter
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