linux-kernel - Re: [PATCH v2] ARM: staging: bcm2835-audio: interpolate audio delay

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Date:   Sun, 11 Nov 2018 21:18:12 +0100 (CET)
From:   Stefan Wahren <stefan.wahren@...e.com>
To:     Mike Brady <mikebrady@...com.net>, tiwai@...e.de
Cc:     devel@...verdev.osuosl.org, alsa-devel@...a-project.org,
        f.fainelli@...il.com, Eric Anholt <eric@...olt.net>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org, julia.lawall@...6.fr,
        linux-rpi-kernel@...ts.infradead.org,
        nishka.dasgupta_ug18@...oka.edu.in,
        Kirill Marinushkin <k.marinushkin@...il.com>,
        linux-arm-kernel@...ts.infradead.org
Subject: Re: [PATCH v2] ARM: staging: bcm2835-audio: interpolate audio delay

Hi Mike,

> Mike Brady <mikebrady@...com.net> hat am 11. November 2018 um 19:21 geschrieben:
> 
> 
> When the BCM2835 audio output is used, userspace sees a jitter up to 10ms
> in the audio position, aka "delay" -- the number of frames that must
> be output before a new frame would be played.
> Make this a bit nicer for userspace by interpolating the position
> using the CPU clock.
> The overhead is small -- an extra ktime_get() every time a GPU message
> is sent -- and another call and a few calculations whenever the delay
> is sought from userland.
> At 48,000 frames per second, i.e. approximately 20 microseconds per
> frame, it would take a clock inaccuracy of
> 20 microseconds in 10 milliseconds -- 2,000 parts per million --
> to result in an inaccurate estimate, whereas
> crystal- or resonator-based clocks typically have an
> inaccuracy of 10s to 100s of parts per million.
> 
> Signed-off-by: Mike Brady <mikebrady@...com.net>

the former version of your patch has already been applied to staging-next.

Didn't you received Greg's email?

So please rebase your changes.

Stefan