linux-kernel - Re: [PATCH 0/3] clk: sunxi-ng: sun8i: a83t: Use sigma-delta modulation for audio PLL

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Date:   Fri, 8 Dec 2017 10:08:53 +0100
From:   Maxime Ripard <maxime.ripard@...e-electrons.com>
To:     Chen-Yu Tsai <wens@...e.org>
Cc:     Michael Turquette <mturquette@...libre.com>,
        Stephen Boyd <sboyd@...eaurora.org>, linux-clk@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-sunxi@...glegroups.com
Subject: Re: [PATCH 0/3] clk: sunxi-ng: sun8i: a83t: Use sigma-delta
 modulation for audio PLL

On Fri, Dec 08, 2017 at 04:35:09PM +0800, Chen-Yu Tsai wrote:
> Hi,
> 
> This series follows previous improvements for the other Allwinner SoCs to
> improve audio quality, in particular the speed and pitch of audio playback.
> The audio PLLs in Allwinner SoCs cannot produce the correct frequency to
> match the audio sample rate families through integer factors. As such
> the audio is either too fast or too flow.
> 
> This is dealt with by using sigma-delta modulation, a form of fractional-N
> synthesis, on the divider. The parameters used are copied from the BSP
> kernel.
> 
> As these parameters assume that one of the untracked dividers is set to
> 2, we first add a fixed /2 post divider to the PLL, and force the
> untracked divider to /2. Then we introduce the sigma-delta modulation
> parameters.
> 
> This has been tested with SPDIF playback on the Cubietruck Plus, and an
> external PCM5122 DAC from a PiFi DAC 2.0+, connected via I2S to the
> Banana Pi M3. The I2C and I2S support used in this latter test will be
> sent as a separate series later.

Applied, thanks!
Maxime

-- 
Maxime Ripard, Free Electrons
Embedded Linux and Kernel engineering
http://free-electrons.com

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