Re: [PATCH v3] clk: meson: gxbb: Fix the SDM_EN bit for MPLL0 on GXBB

[Jerome Brunet]

On Sun 31 Oct 2021 at 14:50, Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx> 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@xxxxxxxxx>
> Tested-by: Christian Hewitt <christianshewitt@xxxxxxxxx>
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@xxxxxxxxxxxxxx>

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@xxxxxxxxxxxxxx/
> [1] https://patchwork.kernel.org/project/linux-amlogic/patch/20211027185326.1653827-1-martin.blumenstingl@xxxxxxxxxxxxxx/
>
>
>  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,