diff mbox series

[v4,6/8] clk: tegra20: Turn EMC clock gate into divider

Message ID 20180719132132.16153-7-digetx@gmail.com
State Superseded
Headers show
Series Tegra20 External Memory Controller driver | expand

Commit Message

Dmitry Osipenko July 19, 2018, 1:21 p.m. UTC 
Kernel should never gate the EMC clock as it causes immediate lockup, so
removing clk-gate functionality doesn't affect anything. Turning EMC clk
gate into divider allows to implement glitch-less EMC scaling, avoiding
reparenting to a backup clock.

Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
Acked-by: Peter De Schrijver <pdeschrijver@nvidia.com>
---
 drivers/clk/tegra/clk-tegra20.c | 36 ++++++++++++++++++++++++---------
 1 file changed, 26 insertions(+), 10 deletions(-)

Comments

Dmitry Osipenko July 22, 2018, 11:39 a.m. UTC | #1 
On Thursday, 19 July 2018 16:21:30 MSK Dmitry Osipenko wrote:
> Kernel should never gate the EMC clock as it causes immediate lockup, so
> removing clk-gate functionality doesn't affect anything. Turning EMC clk
> gate into divider allows to implement glitch-less EMC scaling, avoiding
> reparenting to a backup clock.
> 
> Signed-off-by: Dmitry Osipenko <digetx@gmail.com>
> Acked-by: Peter De Schrijver <pdeschrijver@nvidia.com>
> ---
>  drivers/clk/tegra/clk-tegra20.c | 36 ++++++++++++++++++++++++---------
>  1 file changed, 26 insertions(+), 10 deletions(-)
> 
> diff --git a/drivers/clk/tegra/clk-tegra20.c
> b/drivers/clk/tegra/clk-tegra20.c index cc857d4d4a86..ebea97016d58 100644
> --- a/drivers/clk/tegra/clk-tegra20.c
> +++ b/drivers/clk/tegra/clk-tegra20.c
> @@ -578,7 +578,6 @@ static struct tegra_clk tegra20_clks[tegra_clk_max]
> __initdata = { [tegra_clk_afi] = { .dt_id = TEGRA20_CLK_AFI, .present =
> true }, [tegra_clk_fuse] = { .dt_id = TEGRA20_CLK_FUSE, .present = true },
> [tegra_clk_kfuse] = { .dt_id = TEGRA20_CLK_KFUSE, .present = true },
> -	[tegra_clk_emc] = { .dt_id = TEGRA20_CLK_EMC, .present = true }, };
> 
>  static unsigned long tegra20_clk_measure_input_freq(void)
> @@ -799,6 +798,31 @@ static struct tegra_periph_init_data
> tegra_periph_nodiv_clk_list[] = {
> TEGRA_INIT_DATA_NODIV("disp2",	mux_pllpdc_clkm, CLK_SOURCE_DISP2, 30, 2,
> 26,  0, TEGRA20_CLK_DISP2), };
> 
> +static void __init tegra20_emc_clk_init(void)
> +{
> +	struct clk *clk;
> +
> +	clk = clk_register_mux(NULL, "emc_mux", mux_pllmcp_clkm,
> +			       ARRAY_SIZE(mux_pllmcp_clkm),
> +			       CLK_SET_RATE_NO_REPARENT,
> +			       clk_base + CLK_SOURCE_EMC,
> +			       30, 2, 0, &emc_lock);
> +
> +	clk = tegra_clk_register_mc("mc", "emc_mux", clk_base + CLK_SOURCE_EMC,
> +				    &emc_lock);
> +	clks[TEGRA20_CLK_MC] = clk;
> +
> +	/*
> +	 * Note that 'emc_mux' source and 'emc' rate shouldn't be changed at
> +	 * the same time due to a HW bug, this won't happen because we're
> +	 * defining 'emc_mux' and 'emc' as distinct clocks.
> +	 */
> +	clk = clk_register_divider(NULL, "emc", "emc_mux", CLK_IS_CRITICAL,
> +				   clk_base + CLK_SOURCE_EMC, 0, 7,
> +				   0, &emc_lock);

Actually this is wrong. The divisor is 8 bits-wide and "lsb denote 0.5x", so 
this is a 7.1 divider. I'll prepare v5.



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diff mbox series

Patch

diff --git a/drivers/clk/tegra/clk-tegra20.c b/drivers/clk/tegra/clk-tegra20.c
index cc857d4d4a86..ebea97016d58 100644
--- a/drivers/clk/tegra/clk-tegra20.c
+++ b/drivers/clk/tegra/clk-tegra20.c
@@ -578,7 +578,6 @@  static struct tegra_clk tegra20_clks[tegra_clk_max] __initdata = {
 	[tegra_clk_afi] = { .dt_id = TEGRA20_CLK_AFI, .present = true },
 	[tegra_clk_fuse] = { .dt_id = TEGRA20_CLK_FUSE, .present = true },
 	[tegra_clk_kfuse] = { .dt_id = TEGRA20_CLK_KFUSE, .present = true },
-	[tegra_clk_emc] = { .dt_id = TEGRA20_CLK_EMC, .present = true },
 };
 
 static unsigned long tegra20_clk_measure_input_freq(void)
@@ -799,6 +798,31 @@  static struct tegra_periph_init_data tegra_periph_nodiv_clk_list[] = {
 	TEGRA_INIT_DATA_NODIV("disp2",	mux_pllpdc_clkm, CLK_SOURCE_DISP2, 30, 2, 26,  0, TEGRA20_CLK_DISP2),
 };
 
+static void __init tegra20_emc_clk_init(void)
+{
+	struct clk *clk;
+
+	clk = clk_register_mux(NULL, "emc_mux", mux_pllmcp_clkm,
+			       ARRAY_SIZE(mux_pllmcp_clkm),
+			       CLK_SET_RATE_NO_REPARENT,
+			       clk_base + CLK_SOURCE_EMC,
+			       30, 2, 0, &emc_lock);
+
+	clk = tegra_clk_register_mc("mc", "emc_mux", clk_base + CLK_SOURCE_EMC,
+				    &emc_lock);
+	clks[TEGRA20_CLK_MC] = clk;
+
+	/*
+	 * Note that 'emc_mux' source and 'emc' rate shouldn't be changed at
+	 * the same time due to a HW bug, this won't happen because we're
+	 * defining 'emc_mux' and 'emc' as distinct clocks.
+	 */
+	clk = clk_register_divider(NULL, "emc", "emc_mux", CLK_IS_CRITICAL,
+				   clk_base + CLK_SOURCE_EMC, 0, 7,
+				   0, &emc_lock);
+	clks[TEGRA20_CLK_EMC] = clk;
+}
+
 static void __init tegra20_periph_clk_init(void)
 {
 	struct tegra_periph_init_data *data;
@@ -812,15 +836,7 @@  static void __init tegra20_periph_clk_init(void)
 	clks[TEGRA20_CLK_AC97] = clk;
 
 	/* emc */
-	clk = clk_register_mux(NULL, "emc_mux", mux_pllmcp_clkm,
-			       ARRAY_SIZE(mux_pllmcp_clkm),
-			       CLK_SET_RATE_NO_REPARENT,
-			       clk_base + CLK_SOURCE_EMC,
-			       30, 2, 0, &emc_lock);
-
-	clk = tegra_clk_register_mc("mc", "emc_mux", clk_base + CLK_SOURCE_EMC,
-				    &emc_lock);
-	clks[TEGRA20_CLK_MC] = clk;
+	tegra20_emc_clk_init();
 
 	/* dsi */
 	clk = tegra_clk_register_periph_gate("dsi", "pll_d", 0, clk_base, 0,