w1: mxc_w1: Add warning for base frequency calculation

Base frequency should be as close as possible to 1 MHz. This patch
adds warnings when clock is unreliable, according to i.MX datasheet.

Signed-off-by: Alexander Shiyan <shc_work@mail.ru>
Acked-by: Evgeniy Polyakov <zbr@ioremap.net>
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

1 files changed, 12 insertions, 2 deletions

diff --git a/drivers/w1/masters/mxc_w1.c b/drivers/w1/masters/mxc_w1.c
index 5de3ca9b0fb9..953168c63392 100644
--- a/drivers/w1/masters/mxc_w1.c
+++ b/drivers/w1/masters/mxc_w1.c
@@ -105,6 +105,7 @@ static u8 mxc_w1_ds2_touch_bit(void *data, u8 bit)
 static int mxc_w1_probe(struct platform_device *pdev)
 {
         struct mxc_w1_device *mdev;
+        unsigned long clkrate;
         struct resource *res;
         unsigned int clkdiv;
         int err = 0;
@@ -118,7 +119,16 @@ static int mxc_w1_probe(struct platform_device *pdev)
         if (IS_ERR(mdev->clk))
                 return PTR_ERR(mdev->clk);
 
-        clkdiv = (clk_get_rate(mdev->clk) / 1000000) - 1;
+        clkrate = clk_get_rate(mdev->clk);
+        if (clkrate < 10000000)
+                dev_warn(&pdev->dev,
+                         "Low clock frequency causes improper function\n");
+
+        clkdiv = DIV_ROUND_CLOSEST(clkrate, 1000000);
+        clkrate /= clkdiv;
+        if ((clkrate < 980000) || (clkrate > 1020000))
+                dev_warn(&pdev->dev,
+                         "Incorrect time base frequency %lu Hz\n", clkrate);
 
         res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
         mdev->regs = devm_ioremap_resource(&pdev->dev, res);
@@ -126,7 +136,7 @@ static int mxc_w1_probe(struct platform_device *pdev)
                 return PTR_ERR(mdev->regs);
 
         clk_prepare_enable(mdev->clk);
-        __raw_writeb(clkdiv, mdev->regs + MXC_W1_TIME_DIVIDER);
+        __raw_writeb(clkdiv - 1, mdev->regs + MXC_W1_TIME_DIVIDER);
 
         mdev->bus_master.data = mdev;
         mdev->bus_master.reset_bus = mxc_w1_ds2_reset_bus;