nvmem: rockchip-efuse: add mutex lock for rk1808 efuse read

The rk1808 efuse read has some issues when several threads start to read
efuse through nvmem file node.

Thread1                                    thread2
1. timing_init
2.  write auto_ctrl
3.    delay                                  timing_init
4.      read status                            write auto_ctrl
5.        if error goto to timing_deinit         delay

The thread1 will read no finish bit and then goto error, the user will
see a "Input/Output Error".

The thread1 do timing deinit will cause thread2 halt on read status, and
the user will never success to do read efuse again.

Change-Id: I3f462afd844686aac153acc0c33215fbd96827a3
Signed-off-by: Jianqun Xu <jay.xu@rock-chips.com>

Author: jayxurockchip

drivers/nvmem/rockchip-efuse.c

@@ -111,6 +111,7 @@ struct rockchip_efuse_chip {
 	struct clk *clk;
 	struct clk *sclk;
 	phys_addr_t phys;
+	struct mutex mutex;
 };
 
 static void rk1808_efuse_timing_init(void __iomem *base)
@@ -160,17 +161,18 @@ static int rockchip_rk1808_efuse_read(void *context, unsigned int offset,
 	u8 *buf;
 	int ret, i = 0;
 
+	mutex_lock(&efuse->mutex);
+
 	ret = clk_prepare_enable(efuse->clk);
 	if (ret < 0) {
 		dev_err(efuse->dev, "failed to prepare/enable efuse pclk\n");
-		return ret;
+		goto out;
 	}
 
 	ret = clk_prepare_enable(efuse->sclk);
 	if (ret < 0) {
-		clk_disable_unprepare(efuse->clk);
 		dev_err(efuse->dev, "failed to prepare/enable efuse sclk\n");
-		return ret;
+		goto err_sclk;
 	}
 
 	addr_start = rounddown(offset, RK1808_NBYTES) / RK1808_NBYTES;
@@ -207,8 +209,11 @@ static int rockchip_rk1808_efuse_read(void *context, unsigned int offset,
 	rk1808_efuse_timing_deinit(efuse->base);
 	kfree(buf);
 nomem:
-	clk_disable_unprepare(efuse->clk);
 	clk_disable_unprepare(efuse->sclk);
+err_sclk:
+	clk_disable_unprepare(efuse->clk);
+out:
+	mutex_unlock(&efuse->mutex);
 
 	return ret;
 }
@@ -632,6 +637,8 @@ static int __init rockchip_efuse_probe(struct platform_device *pdev)
 	if (IS_ERR(efuse->sclk))
 		return PTR_ERR(efuse->sclk);
 
+	mutex_init(&efuse->mutex);
+
 	efuse->dev = &pdev->dev;
 	if (of_property_read_u32_index(dev->of_node,
 				       "rockchip,efuse-size",