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Message-ID: <1jilw9g3uz.fsf@starbuckisacylon.baylibre.com>
Date: Tue, 30 Nov 2021 14:38:32 +0100
From: Jerome Brunet <jbrunet@...libre.com>
To: Martin Blumenstingl <martin.blumenstingl@...glemail.com>,
linux-amlogic@...ts.infradead.org
Cc: linux-clk@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org,
Christian Hewitt <christianshewitt@...il.com>
Subject: Re: [PATCH v3] clk: meson: gxbb: Fix the SDM_EN bit for MPLL0 on GXBB
On Sun 31 Oct 2021 at 14:50, Martin Blumenstingl <martin.blumenstingl@...glemail.com> wrote:
> There are reports that 48kHz audio does not work on the WeTek Play 2
> (which uses a GXBB SoC), while 44.1kHz audio works fine on the same
> board. There are also reports of 48kHz audio working fine on GXL and
> GXM SoCs, which are using an (almost) identical AIU (audio controller).
>
> Experimenting has shown that MPLL0 is causing this problem. In the .dts
> we have by default:
> assigned-clocks = <&clkc CLKID_MPLL0>,
> <&clkc CLKID_MPLL1>,
> <&clkc CLKID_MPLL2>;
> assigned-clock-rates = <294912000>,
> <270950400>,
> <393216000>;
> The MPLL0 rate is divisible by 48kHz without remainder and the MPLL1
> rate is divisible by 44.1kHz without remainder. Swapping these two clock
> rates "fixes" 48kHz audio but breaks 44.1kHz audio.
>
> Everything looks normal when looking at the info provided by the common
> clock framework while playing 48kHz audio (via I2S with mclk-fs = 256):
> mpll_prediv 1 1 0 2000000000
> mpll0_div 1 1 0 294909641
> mpll0 1 1 0 294909641
> cts_amclk_sel 1 1 0 294909641
> cts_amclk_div 1 1 0 12287902
> cts_amclk 1 1 0 12287902
>
> meson-clk-msr however shows that the actual MPLL0 clock is off by more
> than 38MHz:
> mp0_out 333322917 +/-10416Hz
>
> The rate seen by meson-clk-msr is very close to what we would get when
> SDM (the fractional part) was ignored:
> (2000000000Hz * 16384) / ((16384 * 6) = 333.33MHz
> If SDM was considered the we should get close to:
> (2000000000Hz * 16384) / ((16384 * 6) + 12808) = 294.9MHz
>
> Further experimenting shows that HHI_MPLL_CNTL7[15] does not have any
> effect on the rate of MPLL0 as seen my meson-clk-msr (regardless of
> whether that bit is zero or one the rate is always the same according to
> meson-clk-msr). Using HHI_MPLL_CNTL[25] on the other hand as SDM_EN
> results in SDM being considered for the rate output by the hardware. The
> rate - as seen by meson-clk-msr - matches with what we expect when
> SDM_EN is enabled (fractional part is being considered, resulting in a
> 294.9MHz output) or disable (fractional part being ignored, resulting in
> a 333.33MHz output).
>
> Reported-by: Christian Hewitt <christianshewitt@...il.com>
> Tested-by: Christian Hewitt <christianshewitt@...il.com>
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@...glemail.com>
Applied. Thx
> ---
> changes since v2 at [1]:
> - add Christian's Tested-by (thank you!)
> - s/his/the/ to fix the grammar in the first sentence as spotted by
> Christian (off-list)
>
> changes since v1 at [0]:
> - consider HHI_MPLL_CNTL[25] as SDM_EN bit after Jerome helped me
> understand the purpose of SDM_EN and gave some explanation why this
> can't be a spread spectrum bit
>
>
> [0] https://patchwork.kernel.org/project/linux-amlogic/patch/20211016145939.15643-1-martin.blumenstingl@googlemail.com/
> [1] https://patchwork.kernel.org/project/linux-amlogic/patch/20211027185326.1653827-1-martin.blumenstingl@googlemail.com/
>
>
> drivers/clk/meson/gxbb.c | 44 +++++++++++++++++++++++++++++++++++++---
> 1 file changed, 41 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/clk/meson/gxbb.c b/drivers/clk/meson/gxbb.c
> index d6eed760327d..608e0e8ca49a 100644
> --- a/drivers/clk/meson/gxbb.c
> +++ b/drivers/clk/meson/gxbb.c
> @@ -713,6 +713,35 @@ static struct clk_regmap gxbb_mpll_prediv = {
> };
>
> static struct clk_regmap gxbb_mpll0_div = {
> + .data = &(struct meson_clk_mpll_data){
> + .sdm = {
> + .reg_off = HHI_MPLL_CNTL7,
> + .shift = 0,
> + .width = 14,
> + },
> + .sdm_en = {
> + .reg_off = HHI_MPLL_CNTL,
> + .shift = 25,
> + .width = 1,
> + },
> + .n2 = {
> + .reg_off = HHI_MPLL_CNTL7,
> + .shift = 16,
> + .width = 9,
> + },
> + .lock = &meson_clk_lock,
> + },
> + .hw.init = &(struct clk_init_data){
> + .name = "mpll0_div",
> + .ops = &meson_clk_mpll_ops,
> + .parent_hws = (const struct clk_hw *[]) {
> + &gxbb_mpll_prediv.hw
> + },
> + .num_parents = 1,
> + },
> +};
> +
> +static struct clk_regmap gxl_mpll0_div = {
> .data = &(struct meson_clk_mpll_data){
> .sdm = {
> .reg_off = HHI_MPLL_CNTL7,
> @@ -749,7 +778,16 @@ static struct clk_regmap gxbb_mpll0 = {
> .hw.init = &(struct clk_init_data){
> .name = "mpll0",
> .ops = &clk_regmap_gate_ops,
> - .parent_hws = (const struct clk_hw *[]) { &gxbb_mpll0_div.hw },
> + .parent_data = &(const struct clk_parent_data) {
> + /*
> + * Note:
> + * GXL and GXBB have different SDM_EN registers. We
> + * fallback to the global naming string mechanism so
> + * mpll0_div picks up the appropriate one.
> + */
> + .name = "mpll0_div",
> + .index = -1,
> + },
> .num_parents = 1,
> .flags = CLK_SET_RATE_PARENT,
> },
> @@ -3044,7 +3082,7 @@ static struct clk_hw_onecell_data gxl_hw_onecell_data = {
> [CLKID_VAPB_1] = &gxbb_vapb_1.hw,
> [CLKID_VAPB_SEL] = &gxbb_vapb_sel.hw,
> [CLKID_VAPB] = &gxbb_vapb.hw,
> - [CLKID_MPLL0_DIV] = &gxbb_mpll0_div.hw,
> + [CLKID_MPLL0_DIV] = &gxl_mpll0_div.hw,
> [CLKID_MPLL1_DIV] = &gxbb_mpll1_div.hw,
> [CLKID_MPLL2_DIV] = &gxbb_mpll2_div.hw,
> [CLKID_MPLL_PREDIV] = &gxbb_mpll_prediv.hw,
> @@ -3439,7 +3477,7 @@ static struct clk_regmap *const gxl_clk_regmaps[] = {
> &gxbb_mpll0,
> &gxbb_mpll1,
> &gxbb_mpll2,
> - &gxbb_mpll0_div,
> + &gxl_mpll0_div,
> &gxbb_mpll1_div,
> &gxbb_mpll2_div,
> &gxbb_cts_amclk_div,
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