Re: [PATCH v2 01/11] clk: tegra: Switch to using critical clks

[Thierry Reding]

On Fri, May 27, 2016 at 04:38:04PM -0400, Rhyland Klein wrote:
> Mark some of the required-to-be-enabled clks as critical clks. These
> need to be kept on through the disabling of unused clks during init.
> They may not get any reference before or after init, but are required
> to be on, therefore let the core enable them.
> 
> Signed-off-by: Rhyland Klein <rklein@xxxxxxxxxx>
> ---
> v2:
>  - Remove mention of HAND_OFF clks as they are not supported yet.
> 
>  drivers/clk/tegra/clk-tegra-periph.c     | 21 ++++++++++++++-------
>  drivers/clk/tegra/clk-tegra-super-gen4.c | 12 +++++++-----
>  2 files changed, 21 insertions(+), 12 deletions(-)

I have some difficulty to follow why some of these clocks are critical.
It might help if the commit message mentioned why each of these need to
remain enabled forever, even if never used.

Also, it's fairly unlikely that pll_p for example would ever get
disabled because a bunch of others are derived from it. I'm also not
quite convinced yet that it really is critical. What does it drive which
isn't claimed by any drivers?

A few more comments below.

> diff --git a/drivers/clk/tegra/clk-tegra-periph.c b/drivers/clk/tegra/clk-tegra-periph.c
> index 29d04c663abf..9365770bcaa5 100644
> --- a/drivers/clk/tegra/clk-tegra-periph.c
> +++ b/drivers/clk/tegra/clk-tegra-periph.c
> @@ -162,6 +162,13 @@
>  			_clk_num, _gate_flags, _clk_id, _parents##_idx, 0,\
>  			NULL)
>  
> +#define MUX8_FLAGS(_name, _parents, _offset,\
> +			     _clk_num, _gate_flags, _clk_id, _flags)	\
> +	TEGRA_INIT_DATA_TABLE(_name, NULL, NULL, _parents, _offset,\
> +			29, MASK(8), 0, 0, 8, 1, TEGRA_DIVIDER_ROUND_UP,\
> +			_clk_num, _gate_flags, _clk_id, _parents##_idx, _flags,\
> +			NULL)
> +
>  #define MUX8_NOGATE_LOCK(_name, _parents, _offset, _clk_id, _lock)	\
>  	TEGRA_INIT_DATA_TABLE(_name, NULL, NULL, _parents, _offset,	\
>  			      29, MASK(3), 0, 0, 8, 1, TEGRA_DIVIDER_ROUND_UP,\
> @@ -651,7 +658,7 @@ static struct tegra_periph_init_data periph_clks[] = {
>  	INT8("3d", mux_pllm_pllc2_c_c3_pllp_plla, CLK_SOURCE_3D, 24, 0, tegra_clk_gr3d_8),
>  	INT8("vic03", mux_pllm_pllc_pllp_plla_pllc2_c3_clkm, CLK_SOURCE_VIC03, 178, 0, tegra_clk_vic03),
>  	INT8("vic03", mux_pllc_pllp_plla1_pllc2_c3_clkm, CLK_SOURCE_VIC03, 178, 0, tegra_clk_vic03_8),
> -	INT_FLAGS("mselect", mux_pllp_clkm, CLK_SOURCE_MSELECT, 99, 0, tegra_clk_mselect, CLK_IGNORE_UNUSED),
> +	INT_FLAGS("mselect", mux_pllp_clkm, CLK_SOURCE_MSELECT, 99, 0, tegra_clk_mselect, CLK_IGNORE_UNUSED | CLK_IS_CRITICAL),

Doesn't CLK_IS_CRITICAL always trump CLK_IGNORE_UNUSED anyway? Why do we
need to keep both?

>  	MUX("i2s0", mux_pllaout0_audio0_2x_pllp_clkm, CLK_SOURCE_I2S0, 30, TEGRA_PERIPH_ON_APB, tegra_clk_i2s0),
>  	MUX("i2s1", mux_pllaout0_audio1_2x_pllp_clkm, CLK_SOURCE_I2S1, 11, TEGRA_PERIPH_ON_APB, tegra_clk_i2s1),
>  	MUX("i2s2", mux_pllaout0_audio2_2x_pllp_clkm, CLK_SOURCE_I2S2, 18, TEGRA_PERIPH_ON_APB, tegra_clk_i2s2),
> @@ -691,8 +698,8 @@ static struct tegra_periph_init_data periph_clks[] = {
>  	MUX("dsiblp", mux_pllp_pllc_clkm, CLK_SOURCE_DSIBLP, 148, 0, tegra_clk_dsiblp),
>  	MUX("tsensor", mux_pllp_pllc_clkm_clk32, CLK_SOURCE_TSENSOR, 100, TEGRA_PERIPH_ON_APB, tegra_clk_tsensor),
>  	MUX("actmon", mux_pllp_pllc_clk32_clkm, CLK_SOURCE_ACTMON, 119, 0, tegra_clk_actmon),
> -	MUX("dfll_ref", mux_pllp_clkm, CLK_SOURCE_DFLL_REF, 155, TEGRA_PERIPH_ON_APB, tegra_clk_dfll_ref),
> -	MUX("dfll_soc", mux_pllp_clkm, CLK_SOURCE_DFLL_SOC, 155, TEGRA_PERIPH_ON_APB, tegra_clk_dfll_soc),
> +	MUX_FLAGS("dfll_ref", mux_pllp_clkm, CLK_SOURCE_DFLL_REF, 155, TEGRA_PERIPH_ON_APB, tegra_clk_dfll_ref, CLK_IS_CRITICAL),
> +	MUX_FLAGS("dfll_soc", mux_pllp_clkm, CLK_SOURCE_DFLL_SOC, 155, TEGRA_PERIPH_ON_APB, tegra_clk_dfll_soc, CLK_IS_CRITICAL),

Aren't these used by the CPU frequency scaling code? Do they have to
remain on if we don't enable CPU frequency scaling?

>  	MUX("i2cslow", mux_pllp_pllc_clk32_clkm, CLK_SOURCE_I2CSLOW, 81, TEGRA_PERIPH_ON_APB, tegra_clk_i2cslow),
>  	MUX("sbc1", mux_pllp_pllc_pllm_clkm, CLK_SOURCE_SBC1, 41, TEGRA_PERIPH_ON_APB, tegra_clk_sbc1),
>  	MUX("sbc2", mux_pllp_pllc_pllm_clkm, CLK_SOURCE_SBC2, 44, TEGRA_PERIPH_ON_APB, tegra_clk_sbc2),
> @@ -730,7 +737,7 @@ static struct tegra_periph_init_data periph_clks[] = {
>  	MUX8("ndflash", mux_pllp_pllc2_c_c3_pllm_clkm, CLK_SOURCE_NDFLASH, 13, TEGRA_PERIPH_ON_APB, tegra_clk_ndflash_8),
>  	MUX8("ndspeed", mux_pllp_pllc2_c_c3_pllm_clkm, CLK_SOURCE_NDSPEED, 80, TEGRA_PERIPH_ON_APB, tegra_clk_ndspeed_8),
>  	MUX8("hdmi", mux_pllp_pllm_plld_plla_pllc_plld2_clkm, CLK_SOURCE_HDMI, 51, 0, tegra_clk_hdmi),
> -	MUX8("extern1", mux_plla_clk32_pllp_clkm_plle, CLK_SOURCE_EXTERN1, 120, 0, tegra_clk_extern1),
> +	MUX8_FLAGS("extern1", mux_plla_clk32_pllp_clkm_plle, CLK_SOURCE_EXTERN1, 120, 0, tegra_clk_extern1, CLK_IS_CRITICAL),

Would you mind refreshing my memory about what this is and why it is
critical?

> @@ -825,7 +832,7 @@ static struct tegra_periph_init_data gate_clks[] = {
>  	GATE("pllg_ref", "pll_ref", 189, 0, tegra_clk_pll_g_ref, 0),
>  	GATE("hsic_trk", "usb2_hsic_trk", 209, TEGRA_PERIPH_NO_RESET, tegra_clk_hsic_trk, 0),
>  	GATE("usb2_trk", "usb2_hsic_trk", 210, TEGRA_PERIPH_NO_RESET, tegra_clk_usb2_trk, 0),
> -	GATE("xusb_gate", "osc", 143, 0, tegra_clk_xusb_gate, 0),
> +	GATE("xusb_gate", "osc", 143, 0, tegra_clk_xusb_gate, CLK_IS_CRITICAL),

Wouldn't this better be handled by the XUSB driver? It certainly seems
very specific to XUSB and I don't see why we would want to keep it
enabled even if XUSB wasn't used.

>  	GATE("pll_p_out_cpu", "pll_p", 223, 0, tegra_clk_pll_p_out_cpu, 0),
>  	GATE("pll_p_out_adsp", "pll_p", 187, 0, tegra_clk_pll_p_out_adsp, 0),
>  	GATE("apb2ape", "clk_m", 107, 0, tegra_clk_apb2ape, 0),
> diff --git a/drivers/clk/tegra/clk-tegra-super-gen4.c b/drivers/clk/tegra/clk-tegra-super-gen4.c
> index 474de0f0c26d..5283138af093 100644
> --- a/drivers/clk/tegra/clk-tegra-super-gen4.c
> +++ b/drivers/clk/tegra/clk-tegra-super-gen4.c
> @@ -116,7 +116,7 @@ static void __init tegra_sclk_init(void __iomem *clk_base,
>  		clk = tegra_clk_register_super_mux("sclk_mux",
>  						gen_info->sclk_parents,
>  						gen_info->num_sclk_parents,
> -						CLK_SET_RATE_PARENT,
> +						CLK_SET_RATE_PARENT | CLK_IS_CRITICAL,
>  						clk_base + SCLK_BURST_POLICY,
>  						0, 4, 0, 0, NULL);
>  		*dt_clk = clk;
> @@ -137,7 +137,8 @@ static void __init tegra_sclk_init(void __iomem *clk_base,
>  			clk = tegra_clk_register_super_mux("sclk",
>  						gen_info->sclk_parents,
>  						gen_info->num_sclk_parents,
> -						CLK_SET_RATE_PARENT,
> +						CLK_SET_RATE_PARENT |
> +						CLK_IS_CRITICAL,
>  						clk_base + SCLK_BURST_POLICY,
>  						0, 4, 0, 0, NULL);
>  			*dt_clk = clk;
> @@ -166,7 +167,8 @@ static void __init tegra_sclk_init(void __iomem *clk_base,
>  				   clk_base + SYSTEM_CLK_RATE, 0, 2, 0,
>  				   &sysrate_lock);
>  	clk = clk_register_gate(NULL, "pclk", "pclk_div", CLK_SET_RATE_PARENT |
> -				CLK_IGNORE_UNUSED, clk_base + SYSTEM_CLK_RATE,
> +				CLK_IGNORE_UNUSED | CLK_IS_CRITICAL,
> +				clk_base + SYSTEM_CLK_RATE,
>  				3, CLK_GATE_SET_TO_DISABLE, &sysrate_lock);
>  	*dt_clk = clk;
>  }

Same comments as for pll_p.

> @@ -187,14 +189,14 @@ static void __init tegra_super_clk_init(void __iomem *clk_base,
>  			clk = tegra_clk_register_super_mux("cclk_g",
>  					gen_info->cclk_g_parents,
>  					gen_info->num_cclk_g_parents,
> -					CLK_SET_RATE_PARENT,
> +					CLK_SET_RATE_PARENT | CLK_IS_CRITICAL,
>  					clk_base + CCLKG_BURST_POLICY,
>  					0, 4, 8, 0, NULL);
>  		} else {
>  			clk = tegra_clk_register_super_mux("cclk_g",
>  					gen_info->cclk_g_parents,
>  					gen_info->num_cclk_g_parents,
> -					CLK_SET_RATE_PARENT,
> +					CLK_SET_RATE_PARENT | CLK_IS_CRITICAL,
>  					clk_base + CCLKG_BURST_POLICY,
>  					0, 4, 0, 0, NULL);
>  		}

I thought this was driving the G cluster, what if we switched to the LP
cluster, wouldn't that mean we can disable cclk_g?

I've only briefly scanned through the remainder of the series, and I
suspect that many of the below changes are simply moving the data out of
the init tables, so not effectively changing anything, but I'd still
like to get this documented a little better. As it is, it's completely
non-obvious why some of these clocks have the CLK_IS_CRITICAL flag while
others don't. It's almost as obfuscated in the current init tables, but
them being in those tables indicates that they're somehow special,
whereas that's much more difficult to see with the conversion to the
CLK_IS_CRITICAL flag.

Thierry

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