clk: meson: meson8b: add support for the NAND clocks

This adds the NAND clocks (from the HHI_NAND_CLK_CNTL register) to the
Meson8b clock driver. There are three NAND clocks: a gate which enables
or disables the NAND clock, a mux and a divider (which divides the mux
output).
Unfortunately the public S805 datasheet does not document the mux
parents. However, the vendor kernel has a few hints for us which allows
us to make an educated guess about the clock parents. To do this we need
to have a look at set_nand_core_clk() from the vendor's NAND driver (see
[0]):
- XTAL = (4<<9) | (1<<8) | 0
- 160MHz = (0<<9) | (1<<8) | 3)
- 182MHz = (3<<9) | (1<<8) | 1)
- 212MHz = (1<<9) | (1<<8) | 3)
- 255MHz = (2<<9) | (1<<8) | 1)

While there is a comment for the XTAL parent (which indicates that it
should only be used for debugging) we have to do a bit of math for the
other parents: target_freq * divider = rate of parent clock
Bit 8 above is the enable bit, so we can ignore it here. Bits 11:9 are
the mux index and bits 6:0 are the 0-based divider (so we need to add
1). This gives us:
- mux 0 (160MHz * 4) = fclk_div4 (actual rate = 637.5MHz, off by 2.5MHz)
- mux 1 (212MHz * 4) = fclk_div3 (actual rate = 850MHz, off by 2MHz)
- mux 2 (255MHz * 2) = fclk_div5 (matches exactly 510MHz)
- mux 3 (182MHz * 2) = fclk_div7 (actual rate = 346.3MHz, off by 0.3MHz)

[0] https://github.com/khadas/linux/blob/9587681285cb/drivers/amlogic/amlnf/dev/amlnf_ctrl.c#L314

Signed-off-by: Martin Blumenstingl <martin.blumenstingl@googlemail.com>
Signed-off-by: Jerome Brunet <jbrunet@baylibre.com>

drivers/clk/meson/meson8b.c

@@ -639,6 +639,54 @@ static struct clk_regmap meson8b_cpu_clk = {
 	},
 };
 
+static struct clk_regmap meson8b_nand_clk_sel = {
+	.data = &(struct clk_regmap_mux_data){
+		.offset = HHI_NAND_CLK_CNTL,
+		.mask = 0x7,
+		.shift = 9,
+		.flags = CLK_MUX_ROUND_CLOSEST,
+	},
+	.hw.init = &(struct clk_init_data){
+		.name = "nand_clk_sel",
+		.ops = &clk_regmap_mux_ops,
+		/* FIXME all other parents are unknown: */
+		.parent_names = (const char *[]){ "fclk_div4", "fclk_div3",
+			"fclk_div5", "fclk_div7", "xtal" },
+		.num_parents = 5,
+		.flags = CLK_SET_RATE_PARENT,
+	},
+};
+
+static struct clk_regmap meson8b_nand_clk_div = {
+	.data = &(struct clk_regmap_div_data){
+		.offset =  HHI_NAND_CLK_CNTL,
+		.shift = 0,
+		.width = 7,
+		.flags = CLK_DIVIDER_ROUND_CLOSEST,
+	},
+	.hw.init = &(struct clk_init_data){
+		.name = "nand_clk_div",
+		.ops = &clk_regmap_divider_ops,
+		.parent_names = (const char *[]){ "nand_clk_sel" },
+		.num_parents = 1,
+		.flags = CLK_SET_RATE_PARENT,
+	},
+};
+
+static struct clk_regmap meson8b_nand_clk_gate = {
+	.data = &(struct clk_regmap_gate_data){
+		.offset = HHI_NAND_CLK_CNTL,
+		.bit_idx = 8,
+	},
+	.hw.init = &(struct clk_init_data){
+		.name = "nand_clk_gate",
+		.ops = &clk_regmap_gate_ops,
+		.parent_names = (const char *[]){ "nand_clk_div" },
+		.num_parents = 1,
+		.flags = CLK_SET_RATE_PARENT,
+	},
+};
+
 /* Everything Else (EE) domain gates */
 
 static MESON_GATE(meson8b_ddr, HHI_GCLK_MPEG0, 0);
@@ -834,6 +882,9 @@ static struct clk_hw_onecell_data meson8b_hw_onecell_data = {
 		[CLKID_FCLK_DIV4_DIV]	    = &meson8b_fclk_div4_div.hw,
 		[CLKID_FCLK_DIV5_DIV]	    = &meson8b_fclk_div5_div.hw,
 		[CLKID_FCLK_DIV7_DIV]	    = &meson8b_fclk_div7_div.hw,
+		[CLKID_NAND_SEL]	    = &meson8b_nand_clk_sel.hw,
+		[CLKID_NAND_DIV]	    = &meson8b_nand_clk_div.hw,
+		[CLKID_NAND_CLK]	    = &meson8b_nand_clk_gate.hw,
 		[CLK_NR_CLKS]		    = NULL,
 	},
 	.num = CLK_NR_CLKS,
@@ -939,6 +990,9 @@ static struct clk_regmap *const meson8b_clk_regmaps[] = {
 	&meson8b_fclk_div4,
 	&meson8b_fclk_div5,
 	&meson8b_fclk_div7,
+	&meson8b_nand_clk_sel,
+	&meson8b_nand_clk_div,
+	&meson8b_nand_clk_gate,
 };
 
 static const struct meson8b_clk_reset_line {