linux-kernel - [PATCH v7 1/5] omap3isp: Modify clocks registration to avoid circular references

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Date:	Tue, 29 Oct 2013 20:51:04 +0100
From:	Sylwester Nawrocki <s.nawrocki@...sung.com>
To:	linux-arm-kernel@...ts.infradead.org, mturquette@...aro.org
Cc:	linux@....linux.org.uk, jiada_wang@...tor.com,
	kyungmin.park@...sung.com, laurent.pinchart@...asonboard.com,
	linux-kernel@...r.kernel.org,
	uclinux-dist-devel@...ckfin.uclinux.org, linux-mips@...ux-mips.org,
	linux-sh@...r.kernel.org,
	Sylwester Nawrocki <s.nawrocki@...sung.com>
Subject: [PATCH v7 1/5] omap3isp: Modify clocks registration to avoid circular
 references

The clock core code is going to be modified so clk_get() takes
reference on the clock provider module. Until the potential circular
reference issue is properly addressed, we pass NULL as as the first
argument to clk_register(), in order to disallow sub-devices taking
a reference on the ISP module back trough clk_get(). This should
prevent locking the modules in memory.

Cc: Laurent Pinchart <laurent.pinchart@...asonboard.com>
Signed-off-by: Sylwester Nawrocki <s.nawrocki@...sung.com>
Signed-off-by: Kyungmin Park <kyungmin.park@...sung.com>
---
This patch has been "compile tested" only.

---
 drivers/media/platform/omap3isp/isp.c |   22 ++++++++++++++++------
 drivers/media/platform/omap3isp/isp.h |    1 +
 2 files changed, 17 insertions(+), 6 deletions(-)

diff --git a/drivers/media/platform/omap3isp/isp.c b/drivers/media/platform/omap3isp/isp.c
index df3a0ec..286027a 100644
--- a/drivers/media/platform/omap3isp/isp.c
+++ b/drivers/media/platform/omap3isp/isp.c
@@ -290,9 +290,11 @@ static int isp_xclk_init(struct isp_device *isp)
 	struct clk_init_data init;
 	unsigned int i;

+	for (i = 0; i < ARRAY_SIZE(isp->xclks); ++i)
+		isp->xclks[i].clk = ERR_PTR(-EINVAL);
+
 	for (i = 0; i < ARRAY_SIZE(isp->xclks); ++i) {
 		struct isp_xclk *xclk = &isp->xclks[i];
-		struct clk *clk;

 		xclk->isp = isp;
 		xclk->id = i == 0 ? ISP_XCLK_A : ISP_XCLK_B;
@@ -305,10 +307,15 @@ static int isp_xclk_init(struct isp_device *isp)
 		init.num_parents = 1;

 		xclk->hw.init = &init;
-
-		clk = devm_clk_register(isp->dev, &xclk->hw);
-		if (IS_ERR(clk))
-			return PTR_ERR(clk);
+		/*
+		 * The first argument is NULL in order to avoid circular
+		 * reference, as this driver takes reference on the
+		 * sensor subdevice modules and the sensors would take
+		 * reference on this module through clk_get().
+		 */
+		xclk->clk = clk_register(NULL, &xclk->hw);
+		if (IS_ERR(xclk->clk))
+			return PTR_ERR(xclk->clk);

 		if (pdata->xclks[i].con_id == NULL &&
 		    pdata->xclks[i].dev_id == NULL)
@@ -320,7 +327,7 @@ static int isp_xclk_init(struct isp_device *isp)

 		xclk->lookup->con_id = pdata->xclks[i].con_id;
 		xclk->lookup->dev_id = pdata->xclks[i].dev_id;
-		xclk->lookup->clk = clk;
+		xclk->lookup->clk = xclk->clk;

 		clkdev_add(xclk->lookup);
 	}
@@ -335,6 +342,9 @@ static void isp_xclk_cleanup(struct isp_device *isp)
 	for (i = 0; i < ARRAY_SIZE(isp->xclks); ++i) {
 		struct isp_xclk *xclk = &isp->xclks[i];

+		if (!IS_ERR(xclk->clk))
+			clk_unregister(xclk->clk);
+
 		if (xclk->lookup)
 			clkdev_drop(xclk->lookup);
 	}
diff --git a/drivers/media/platform/omap3isp/isp.h b/drivers/media/platform/omap3isp/isp.h
index cd3eff4..1498f2b 100644
--- a/drivers/media/platform/omap3isp/isp.h
+++ b/drivers/media/platform/omap3isp/isp.h
@@ -135,6 +135,7 @@ struct isp_xclk {
 	struct isp_device *isp;
 	struct clk_hw hw;
 	struct clk_lookup *lookup;
+	struct clk *clk;
 	enum isp_xclk_id id;

 	spinlock_t lock;	/* Protects enabled and divider */
--
1.7.9.5

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