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Re: [PATCH v6 0/5] clk: clock deregistration support

To: linux@arm.linux.org.uk, mturquette@linaro.org
Subject: Re: [PATCH v6 0/5] clk: clock deregistration support
From: Sylwester Nawrocki <sylvester.nawrocki@gmail.com>
Date: Tue, 24 Sep 2013 23:38:44 +0200
Cc: Sylwester Nawrocki <s.nawrocki@samsung.com>, linux-arm-kernel@lists.infradead.org, jiada_wang@mentor.com, kyungmin.park@samsung.com, myungjoo.ham@samsung.com, t.figa@samsung.com, g.liakhovetski@gmx.de, laurent.pinchart@ideasonboard.com, linux-kernel@vger.kernel.org, linux-mips@linux-mips.org, linux-sh@vger.kernel.org
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On 08/30/2013 04:53 PM, Sylwester Nawrocki wrote:
This patch series implements clock deregistration in the common clock
framework. Comparing to v5 it only includes further corrections of NULL
clock handling.
[...]
   clk: Provide not locked variant of of_clk_get_from_provider()
   clkdev: Fix race condition in clock lookup from device tree
   clk: Add common __clk_get(), __clk_put() implementations
   clk: Assign module owner of a clock being registered
   clk: Implement clk_unregister

Hi Mike, Russell,

Would you have any further comments/suggestions on this series ?

I have inspected all callers of clk_register() and all should be fine
with regards to dereferencing dev->driver. The first argument to this
function is either NULL or clk_register() is being called in drivers'
probe() callback, which ensures dev->driver won't change due to holding
dev->mutex.

The only issue I found might be at the omap3isp driver, which provides
clock to its sub-drivers and takes reference on the sub-driver modules.
When sub-driver calls clk_get() all modules would get locked in memory,
due to circular reference. One solution to that could be to pass NULL
struct device pointer, as in the below patch.

---------8<------------------
From ca5963041aad67e31324cb5d4d5e2cfce1706d4f Mon Sep 17 00:00:00 2001
From: Sylwester Nawrocki <s.nawrocki@samsung.com>
Date: Thu, 19 Sep 2013 23:52:04 +0200
Subject: [PATCH] omap3isp: Pass NULL device pointer to clk_register()

Signed-off-by: Sylwester Nawrocki <s.nawrocki@samsung.com>
---
 drivers/media/platform/omap3isp/isp.c |   15 ++++++++++-----
 drivers/media/platform/omap3isp/isp.h |    1 +
 2 files changed, 11 insertions(+), 5 deletions(-)

diff --git a/drivers/media/platform/omap3isp/isp.c b/drivers/media/platform/omap3isp/isp.c
index df3a0ec..d7f3c98 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] = 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;
@@ -306,9 +308,9 @@ static int isp_xclk_init(struct isp_device *isp)

                xclk->hw.init = &init;

-               clk = devm_clk_register(isp->dev, &xclk->hw);
-               if (IS_ERR(clk))
-                       return PTR_ERR(clk);
+               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 +322,7 @@ 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 +337,9 @@ 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 */
--
---------8<------------------


Alternatively an additional argument could be added to the clk_register*()
functions. Something like:

---------8<------------------
diff --git a/drivers/clk/clk.c b/drivers/clk/clk.c
index 27f8c42..ef934ac 100644
--- a/drivers/clk/clk.c
+++ b/drivers/clk/clk.c
@@ -1837,7 +1837,8 @@ struct clk *__clk_register(struct device *dev, struct clk_hw *hw)
 }
 EXPORT_SYMBOL_GPL(__clk_register);

-static int _clk_register(struct device *dev, struct clk_hw *hw, struct clk *clk) +static int _clk_register(struct device *dev, struct clk_hw *hw, struct clk *clk,
+                                                       struct module *owner)
 {
        int i, ret;

@@ -1877,6 +1878,8 @@ static int _clk_register(struct device *dev, struct clk_hw *hw, struct clk *clk)
                }
        }

+       clk->owner = owner;
+
        ret = __clk_init(dev, clk);
        if (!ret)
                return 0;
@@ -1892,7 +1895,7 @@ fail_name:
 }

 /**
- * clk_register - allocate a new clock, register it and return an opaque cookie + * ___clk_register - allocate a new clock, register it and return an opaque cookie
  * @dev: device that is registering this clock
  * @hw: link to hardware-specific clock data
  *
@@ -1902,7 +1905,8 @@ fail_name:
* rest of the clock API. In the event of an error clk_register will return an * error code; drivers must test for an error code after calling clk_register.
  */
-struct clk *clk_register(struct device *dev, struct clk_hw *hw)
+struct clk *___clk_register(struct device *dev, struct clk_hw *hw,
+                                               struct module *owner)
 {
        int ret;
        struct clk *clk;
@@ -1914,7 +1918,7 @@ struct clk *clk_register(struct device *dev, struct clk_hw *hw)
                goto fail_out;
        }

-       ret = _clk_register(dev, hw, clk);
+       ret = _clk_register(dev, hw, clk, owner);
        if (!ret)
                return clk;

@@ -1922,7 +1926,7 @@ struct clk *clk_register(struct device *dev, struct clk_hw *hw)
 fail_out:
        return ERR_PTR(ret);
 }
-EXPORT_SYMBOL_GPL(clk_register);
+EXPORT_SYMBOL_GPL(___clk_register);

 /*
  * Free memory allocated for a clock.
@@ -2040,7 +2044,8 @@ static void devm_clk_release(struct device *dev, void *res) * automatically clk_unregister()ed on driver detach. See clk_register() for
  * more information.
  */
-struct clk *devm_clk_register(struct device *dev, struct clk_hw *hw)
+struct clk *__devm_clk_register(struct device *dev, struct clk_hw *hw,
+                                               struct module *owner)
 {
        struct clk *clk;
        int ret;
@@ -2049,7 +2054,7 @@ struct clk *devm_clk_register(struct device *dev, struct clk_hw *hw)
        if (!clk)
                return ERR_PTR(-ENOMEM);

-       ret = _clk_register(dev, hw, clk);
+       ret = _clk_register(dev, hw, clk, owner);
        if (!ret) {
                devres_add(dev, clk);
        } else {
@@ -2059,7 +2064,7 @@ struct clk *devm_clk_register(struct device *dev, struct clk_hw *hw)

        return clk;
 }
-EXPORT_SYMBOL_GPL(devm_clk_register);
+EXPORT_SYMBOL_GPL(__devm_clk_register);

 static int devm_clk_match(struct device *dev, void *res, void *data)
 {
diff --git a/include/linux/clk-provider.h b/include/linux/clk-provider.h
index 13623f3..c656ebf 100644
--- a/include/linux/clk-provider.h
+++ b/include/linux/clk-provider.h
@@ -31,6 +31,7 @@
#define CLK_SET_RATE_NO_REPARENT BIT(7) /* don't re-parent on rate change */

 struct clk_hw;
+struct module;

 /**
  * struct clk_ops -  Callback operations for hardware clocks; these are to
@@ -436,8 +437,21 @@ struct clk *clk_register_composite(struct device *dev, const char *name, * rest of the clock API. In the event of an error clk_register will return an * error code; drivers must test for an error code after calling clk_register.
  */
-struct clk *clk_register(struct device *dev, struct clk_hw *hw);
-struct clk *devm_clk_register(struct device *dev, struct clk_hw *hw);
+struct clk *___clk_register(struct device *dev, struct clk_hw *hw,
+               struct module *owner);
+
+static inline struct clk *clk_register(struct device *dev, struct clk_hw *hw)
+{
+       return ___clk_register(dev, hw, THIS_MODULE);
+}
+
+struct clk *__devm_clk_register(struct device *dev, struct clk_hw *hw,
+                               struct module *owner);
+static inline struct clk *devm_clk_register(struct device *dev,
+                                           struct clk_hw *hw)
+{
+       return __devm_clk_register(dev, hw, THIS_MODULE);
+}

 void clk_unregister(struct clk *clk);
 void devm_clk_unregister(struct device *dev, struct clk *clk);

---------8<------------------

Similarly it would need to be done for the remaining clk_register*() functions,
which have much longer arguments list.

It's a bit messy, since there is already __clk_register() function with double underscore prefix. Perhaps that could be renamed to something else so all the functions taking struct module * parameter are prefixed with double underscore.


I would squash patches 3/5 and 4/5 in the next iteration, if it is decided
to keep using dev->driver->owner.

--
Thanks,
Sylwester

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