linux-kernel - [PATCH 1/2] amba: Take device out of reset before reading pid and cid values

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Message-Id: <20190309015635.5401-2-manivannan.sadhasivam@linaro.org>
Date:   Sat,  9 Mar 2019 07:26:34 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     linux@...linux.org.uk, xuwei5@...ilicon.com
Cc:     linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        linus.walleij@...aro.org, daniel.thompson@...aro.org,
        peter.griffin@...aro.org, guodong.xu@...aro.org,
        haojian.zhuang@...aro.org,
        Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
Subject: [PATCH 1/2] amba: Take device out of reset before reading pid and cid values

For the AMBA Primecell devices having the reset lines wired, it is
necessary to take them out of reset before reading the pid and cid values.
Earlier we were dependent on the bootloader to do this but a more cleaner
approach would be to do it in the kernel itself. Hence, this commit
deasserts the reset line just before reading the pid and cid values.

Suggested-by: Daniel Thompson <daniel.thompson@...aro.org>
Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
---
 drivers/amba/bus.c | 9 +++++++++
 1 file changed, 9 insertions(+)

diff --git a/drivers/amba/bus.c b/drivers/amba/bus.c
index 41b706403ef7..da8f1aac5315 100644
--- a/drivers/amba/bus.c
+++ b/drivers/amba/bus.c
@@ -21,6 +21,7 @@
 #include <linux/limits.h>
 #include <linux/clk/clk-conf.h>
 #include <linux/platform_device.h>
+#include <linux/reset.h>
 
 #include <asm/irq.h>
 
@@ -352,6 +353,7 @@ static void amba_device_release(struct device *dev)
 
 static int amba_device_try_add(struct amba_device *dev, struct resource *parent)
 {
+	struct reset_control *rst;
 	u32 size;
 	void __iomem *tmp;
 	int i, ret;
@@ -388,6 +390,13 @@ static int amba_device_try_add(struct amba_device *dev, struct resource *parent)
 	if (ret == 0) {
 		u32 pid, cid;
 
+		/* De-assert the reset line to take the device out of reset */
+		rst = reset_control_get_optional_exclusive(&dev->dev, NULL);
+		if (IS_ERR(rst))
+			return PTR_ERR(rst);
+
+		reset_control_deassert(rst);
+
 		/*
 		 * Read pid and cid based on size of resource
 		 * they are located at end of region
-- 
2.17.1