Re: [PATCH] clk: meson: gxbb: Add the spread spectrum bit for MPLL0 on GXBB

[Christian Hewitt <christianshewitt@gmail.com>]

> On 16 Oct 2021, at 6:59 pm, Martin Blumenstingl <martin.blumenstingl@googlemail.com> wrote:
> 
> Christian reports that 48kHz audio does not work on his WeTek Play 2
> (which uses a GXBB SoC), while 44.1kHz audio works fine on the same
> board. He also reports that 48kHz audio works 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 3.14 vendor kernel uses the following code to enable SSEN only for
> MPLL0 (where con_reg2 is HHI_MPLL_CNTL and SSEN_shift is 25):
> 	if (strncmp(hw->clk->name, "mpll_clk_out0", 13) == 0) {
> 		val = readl(mpll->con_reg2);
> 		val |= 1 <<  mpll->SSEN_shift;
> 		writel(val, mpll->con_reg2);
> 	}
> 
> Add the SSEN (spread spectrum enable) bit and add the
> CLK_MESON_MPLL_SPREAD_SPECTRUM flag to enable this bit for MPLL0. Do
> this for GXBB *only* since GXL doesn't seem to care if this bit is set
> or not, meaning that meson-clk-msr always sees (approximately) the same
> frequency as common clock framework.
> 
> Fixes: 8925dbd03bb29b ("clk: meson: gxbb: no spread spectrum on mpll")
> Reported-by: Christian Hewitt <christianshewitt@gmail.com>
> Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>

Tested with a selection of different media at 41KHz and 48KHz on GXBB
(WeTek Play2 and Hub) and GXL (LePotato).

Tested-by: Christian Hewitt <christianshewitt@gmail.com>

> ---
> drivers/clk/meson/gxbb.c | 50 +++++++++++++++++++++++++++++++++++++---
> 1 file changed, 47 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/clk/meson/gxbb.c b/drivers/clk/meson/gxbb.c
> index d6eed760327d..673bc915c7d9 100644
> --- a/drivers/clk/meson/gxbb.c
> +++ b/drivers/clk/meson/gxbb.c
> @@ -713,6 +713,41 @@ 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_CNTL7,
> +			.shift   = 15,
> +			.width	 = 1,
> +		},
> +		.n2 = {
> +			.reg_off = HHI_MPLL_CNTL7,
> +			.shift   = 16,
> +			.width   = 9,
> +		},
> +		.ssen = {
> +			.reg_off = HHI_MPLL_CNTL,
> +			.shift   = 25,
> +			.width   = 1,
> +		},
> +		.flags = CLK_MESON_MPLL_SPREAD_SPECTRUM,
> +		.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 +784,16 @@ 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 SSEN requirements. 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 +3088,7 @@ 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 +3483,7 @@ 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,
> -- 
> 2.33.1
>