ARM i.MX6: change mxs usbphy clock usage

This mxs usbphy is only needs to be on after system boots
up, and software never needs to control it anymore.
Meanwhile, usbphy's parent needs to be notified if usb
is suspend or not. So we design below mxs usbphy usage:

- usbphy1_gate and usbphy2_gate:
Their parents are dummy clock, we only needs to enable
it after system boots up.
- usbphy1 and usbphy2
Usage reserved bit for this clock, in that case, the refcount
will be updated, but without hardware changing.
Signed-off-by: NPeter Chen <peter.chen@freescale.com>
Signed-off-by: NShawn Guo <shawn.guo@linaro.org>

Documentation/devicetree/bindings/clock/imx6q-clock.txt

@@ -203,6 +203,8 @@ clocks and IDs.
 	pcie_ref		188
 	pcie_ref_125m		189
 	enet_ref		190
+	usbphy1_gate		191
+	usbphy2_gate		192
 
 Examples:
 

arch/arm/mach-imx/clk-imx6q.c

@@ -154,8 +154,8 @@ enum mx6q_clks {
 	usdhc4, vdo_axi, vpu_axi, cko1, pll1_sys, pll2_bus, pll3_usb_otg,
 	pll4_audio, pll5_video, pll8_mlb, pll7_usb_host, pll6_enet, ssi1_ipg,
 	ssi2_ipg, ssi3_ipg, rom, usbphy1, usbphy2, ldb_di0_div_3_5, ldb_di1_div_3_5,
-	sata_ref, sata_ref_100m, pcie_ref, pcie_ref_125m, enet_ref,
-	clk_max
+	sata_ref, sata_ref_100m, pcie_ref, pcie_ref_125m, enet_ref, usbphy1_gate,
+	usbphy2_gate, clk_max
 };
 
 static struct clk *clk[clk_max];
@@ -208,8 +208,21 @@ int __init mx6q_clocks_init(void)
 	clk[pll7_usb_host] = imx_clk_pllv3(IMX_PLLV3_USB,	"pll7_usb_host","osc", base + 0x20, 0x3);
 	clk[pll8_mlb]      = imx_clk_pllv3(IMX_PLLV3_MLB,	"pll8_mlb",	"osc", base + 0xd0, 0x0);
 
-	clk[usbphy1] = imx_clk_gate("usbphy1", "pll3_usb_otg", base + 0x10, 6);
-	clk[usbphy2] = imx_clk_gate("usbphy2", "pll7_usb_host", base + 0x20, 6);
+	/*
+	 * Bit 20 is the reserved and read-only bit, we do this only for:
+	 * - Do nothing for usbphy clk_enable/disable
+	 * - Keep refcount when do usbphy clk_enable/disable, in that case,
+	 * the clk framework may need to enable/disable usbphy's parent
+	 */
+	clk[usbphy1] = imx_clk_gate("usbphy1", "pll3_usb_otg", base + 0x10, 20);
+	clk[usbphy2] = imx_clk_gate("usbphy2", "pll7_usb_host", base + 0x20, 20);
+
+	/*
+	 * usbphy*_gate needs to be on after system boots up, and software
+	 * never needs to control it anymore.
+	 */
+	clk[usbphy1_gate] = imx_clk_gate("usbphy1_gate", "dummy", base + 0x10, 6);
+	clk[usbphy2_gate] = imx_clk_gate("usbphy2_gate", "dummy", base + 0x20, 6);
 
 	clk[sata_ref] = imx_clk_fixed_factor("sata_ref", "pll6_enet", 1, 5);
 	clk[pcie_ref] = imx_clk_fixed_factor("pcie_ref", "pll6_enet", 1, 4);
@@ -436,6 +449,11 @@ int __init mx6q_clocks_init(void)
 	for (i = 0; i < ARRAY_SIZE(clks_init_on); i++)
 		clk_prepare_enable(clk[clks_init_on[i]]);
 
+	if (IS_ENABLED(CONFIG_USB_MXS_PHY)) {
+		clk_prepare_enable(clk[usbphy1_gate]);
+		clk_prepare_enable(clk[usbphy2_gate]);
+	}
+
 	/* Set initial power mode */
 	imx6q_set_lpm(WAIT_CLOCKED);