Re: [PATCH RESEND 6/6] clk: s5p-g2d: Fix incorrect usage of IS_ERR_OR_NULL

Julia Lawall
2013-01-02T07:29:57Z

On Wed, 2 Jan 2013, Tony Prisk wrote:

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