On Wed, 2 Jan 2013, Tony Prisk wrote:

On Wed, 2013-01-02 at 08:10 +0300, Dan Carpenter wrote:

quoted

clk_get() returns NULL if CONFIG_HAVE_CLK is disabled.

I told Tony about this but everyone has been gone with end of year
holidays so it hasn't been addressed.

Tony, please fix it so people don't apply these patches until
clk_get() is updated to not return NULL.  It sucks to have to revert
patches.

regards,
dan carpenter

I posted the query to Mike Turquette, linux-kernel and linux-arm-kernel
mailing lists, regarding the return of NULL when HAVE_CLK is undefined.

Short Answer: A return value of NULL is valid and not an error therefore
we should be using IS_ERR, not IS_ERR_OR_NULL on clk_get results.

I see the obvious problem this creates, and asked this question:

If the driver can't operate with a NULL clk, it should use a
IS_ERR_OR_NULL test to test for failure, rather than IS_ERR.


And Russell's answer:

Why should a _consumer_ of a clock care?  It is _very_ important that
people get this idea - to a consumer, the struct clk is just an opaque
cookie.  The fact that it appears to be a pointer does _not_ mean that
the driver can do any kind of dereferencing on that pointer - it should
never do so.

Thread can be viewed here:
https://lkml.org/lkml/2012/12/20/105

There are dereferences to the result of clk_get a few times.  I tried the 
following semantic patch:

@@ expression E; identifier I; @@

* E = clk_get(...) ... E->I

It gives the results shown below (- marks matched lines, not lines to 
remove).  I also tried with devm_clk_get instead of clk_get, but got 
nothing.

julia

diff -u -p /var/linuxes/linux-next/arch/sh/kernel/cpufreq.c /tmp/nothing/arch/sh/kernel/cpufreq.c

--- /var/linuxes/linux-next/arch/sh/kernel/cpufreq.c
+++ /tmp/nothing/arch/sh/kernel/cpufreq.c

@@ -117,15 +117,11 @@ static int sh_cpufreq_cpu_init(struct cp

  	dev = get_cpu_device(cpu);

-	cpuclk = clk_get(dev, "cpu_clk");
-	if (IS_ERR(cpuclk)) {
  		dev_err(dev, "couldn't get CPU clk\n");
  		return PTR_ERR(cpuclk);
  	}

-	policy->cur = policy->min = policy->max = sh_cpufreq_get(cpu);

-	freq_table = cpuclk->nr_freqs ? cpuclk->freq_table : NULL;
  	if (freq_table) {
  		int result;

diff -u -p /var/linuxes/linux-next/arch/mips/kernel/cpufreq/loongson2_cpufreq.c /tmp/nothing/arch/mips/kernel/cpufreq/loongson2_cpufreq.c

--- /var/linuxes/linux-next/arch/mips/kernel/cpufreq/loongson2_cpufreq.c
+++ /tmp/nothing/arch/mips/kernel/cpufreq/loongson2_cpufreq.c

@@ -111,13 +111,10 @@ static int loongson2_cpufreq_cpu_init(st
  	if (!cpu_online(policy->cpu))
  		return -ENODEV;

-	cpuclk = clk_get(NULL, "cpu_clk");
-	if (IS_ERR(cpuclk)) {
  		printk(KERN_ERR "cpufreq: couldn't get CPU clk\n");
  		return PTR_ERR(cpuclk);
  	}

-	cpuclk->rate = cpu_clock_freq / 1000;
  	if (!cpuclk->rate)
  		return -EINVAL;

diff -u -p /var/linuxes/linux-next/drivers/net/ethernet/ti/cpts.c /tmp/nothing/drivers/net/ethernet/ti/cpts.c

--- /var/linuxes/linux-next/drivers/net/ethernet/ti/cpts.c
+++ /tmp/nothing/drivers/net/ethernet/ti/cpts.c

@@ -241,14 +241,10 @@ static void cpts_overflow_check(struct w

  static void cpts_clk_init(struct cpts *cpts)
  {
-	cpts->refclk = clk_get(NULL, CPTS_REF_CLOCK_NAME);
-	if (IS_ERR(cpts->refclk)) {
  		pr_err("Failed to clk_get %s\n", CPTS_REF_CLOCK_NAME);
  		cpts->refclk = NULL;
  		return;
  	}
-	clk_enable(cpts->refclk);
-	cpts->freq = cpts->refclk->recalc(cpts->refclk);
  }

  static void cpts_clk_release(struct cpts *cpts)

diff -u -p /var/linuxes/linux-next/drivers/i2c/busses/i2c-sh7760.c /tmp/nothing/drivers/i2c/busses/i2c-sh7760.c

--- /var/linuxes/linux-next/drivers/i2c/busses/i2c-sh7760.c
+++ /tmp/nothing/drivers/i2c/busses/i2c-sh7760.c

@@ -397,11 +397,7 @@ static int calc_CCR(unsigned long scl_hz
  	signed char cdf, cdfm;
  	int scgd, scgdm, scgds;

-	mclk = clk_get(NULL, "peripheral_clk");
-	if (IS_ERR(mclk)) {
  		return PTR_ERR(mclk);
-	} else {
-		mck = mclk->rate;
  		clk_put(mclk);
  	}