USB: ohci-at91: add usb_clk for transition to common clk framework

The AT91 PMC (Power Management Controller) provides an USB clock used by
USB Full Speed host (ohci) and USB Full Speed device (udc).
The usb drivers (ohci and udc) must configure this clock to 48Mhz.
This configuration was formely done in mach-at91/clock.c, but this
implementation will be removed when moving to common clk framework.

This patch adds support for usb clock retrieval and configuration, and is
backward compatible with the current at91 clk implementation (if usb clk
is not found, it does not configure/enable it).

Changes since v1:
 - use IS_ENABLED(CONFIG_COMMON_CLK) to isolate new at91 clk support
Signed-off-by: Boris BREZILLON <b.brezillon@overkiz.com>
Acked-by: Alan Stern <stern@rowland.harvard.edu>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

drivers/usb/host/ohci-at91.c

@@ -31,8 +31,8 @@
 #define at91_for_each_port(index)	\
 		for ((index) = 0; (index) < AT91_MAX_USBH_PORTS; (index)++)
 
-/* interface and function clocks; sometimes also an AHB clock */
-static struct clk *iclk, *fclk, *hclk;
+/* interface, function and usb clocks; sometimes also an AHB clock */
+static struct clk *iclk, *fclk, *uclk, *hclk;
 static int clocked;
 
 extern int usb_disabled(void);
@@ -41,6 +41,10 @@ extern int usb_disabled(void);
 
 static void at91_start_clock(void)
 {
+	if (IS_ENABLED(CONFIG_COMMON_CLK)) {
+		clk_set_rate(uclk, 48000000);
+		clk_prepare_enable(uclk);
+	}
 	clk_prepare_enable(hclk);
 	clk_prepare_enable(iclk);
 	clk_prepare_enable(fclk);
@@ -52,6 +56,8 @@ static void at91_stop_clock(void)
 	clk_disable_unprepare(fclk);
 	clk_disable_unprepare(iclk);
 	clk_disable_unprepare(hclk);
+	if (IS_ENABLED(CONFIG_COMMON_CLK))
+		clk_disable_unprepare(uclk);
 	clocked = 0;
 }
 
@@ -162,6 +168,14 @@ static int usb_hcd_at91_probe(const struct hc_driver *driver,
 		retval = PTR_ERR(hclk);
 		goto err5;
 	}
+	if (IS_ENABLED(CONFIG_COMMON_CLK)) {
+		uclk = clk_get(&pdev->dev, "usb_clk");
+		if (IS_ERR(uclk)) {
+			dev_err(&pdev->dev, "failed to get uclk\n");
+			retval = PTR_ERR(uclk);
+			goto err6;
+		}
+	}
 
 	at91_start_hc(pdev);
 	ohci_hcd_init(hcd_to_ohci(hcd));
@@ -173,6 +187,9 @@ static int usb_hcd_at91_probe(const struct hc_driver *driver,
 	/* Error handling */
 	at91_stop_hc(pdev);
 
+	if (IS_ENABLED(CONFIG_COMMON_CLK))
+		clk_put(uclk);
+ err6:
 	clk_put(hclk);
  err5:
 	clk_put(fclk);
@@ -212,6 +229,8 @@ static void usb_hcd_at91_remove(struct usb_hcd *hcd,
 	release_mem_region(hcd->rsrc_start, hcd->rsrc_len);
 	usb_put_hcd(hcd);
 
+	if (IS_ENABLED(CONFIG_COMMON_CLK))
+		clk_put(uclk);
 	clk_put(hclk);
 	clk_put(fclk);
 	clk_put(iclk);