[PATCH v2] eeepc-laptop: simplify parse_arg()

Paul Bolle
2014-09-10T20:05:27Z

parse_arg() has three possible return values:
-EINVAL if sscanf(), in short, fails;
zero if "count" is zero; and
"count" in all other cases

But "count" will never be zero. See, parse_arg() is called by the
various store functions. And the callchain of these functions starts
with sysfs_kf_write(). And that function checks for a zero "count". So
we can stop checking for a zero "count", drop the "count" argument
entirely, and transform parse_arg() into a function that returns zero on
success or a negative error. That, in turn, allows to make those store
functions just return "count" on success. The net effect is that the
code becomes a bit easier to understand.

While we're at it, let store_sys_acpi() return whatever error set_acpi()
returns instead of remapping it to EIO.

A nice side effect is that this GCC warning is silenced too:
drivers/platform/x86/eeepc-laptop.c: In function ‘store_sys_acpi’:
drivers/platform/x86/eeepc-laptop.c:279:10: warning: ‘value’ may be used uninitialized in this function [-Wmaybe-uninitialized]
int rv, value;

Which is, of course, the reason to have a look at parse_arg().

Signed-off-by: Paul Bolle <pebolle@tiscali.nl>
---
v2: let store_sys_acpi() return whatever error set_acpi()
returns instead of remapping it to EIO. The new line about that in the
commit explanation is silly, but I couldn't come up with a better
explanation.

Still build tested only on top of v3.17-rc4 (I think Frans actually
tested v1, which is almost identical).

There was a lot of discussion on the errors returned by this driver. I
think using new error codes is actually out of scope for this patch and
should be done in follow up patches.

drivers/platform/x86/eeepc-laptop.c | 38 ++++++++++++++++++-------------------
1 file changed, 19 insertions(+), 19 deletions(-)

diff --git a/drivers/platform/x86/eeepc-laptop.c b/drivers/platform/x86/eeepc-laptop.c
index bd533c22be57..90be993b140e 100644
--- a/drivers/platform/x86/eeepc-laptop.c
+++ b/drivers/platform/x86/eeepc-laptop.c
@@ -263,13 +263,11 @@ static int acpi_setter_handle(struct eeepc_laptop *eeepc, int cm,
/*
* Sys helpers
*/
-static int parse_arg(const char *buf, unsigned long count, int *val)
+static int parse_arg(const char *buf, int *val)
{
- if (!count)
- return 0;
if (sscanf(buf, "%i", val) != 1)
return -EINVAL;
- return count;
+ return 0;
}

static ssize_t store_sys_acpi(struct device *dev, int cm,
@@ -278,12 +276,13 @@ static ssize_t store_sys_acpi(struct device *dev, int cm,
struct eeepc_laptop *eeepc = dev_get_drvdata(dev);
int rv, value;

- rv = parse_arg(buf, count, &value);
- if (rv > 0)
- value = set_acpi(eeepc, cm, value);
- if (value < 0)
- return -EIO;
- return rv;
+ rv = parse_arg(buf, &value);
+ if (rv < 0)
+ return rv;
+ rv = set_acpi(eeepc, cm, value);
+ if (rv < 0)
+ return rv;
+ return count;
}

static ssize_t show_sys_acpi(struct device *dev, int cm, char *buf)
@@ -377,13 +376,13 @@ static ssize_t store_cpufv(struct device *dev,
return -EPERM;
if (get_cpufv(eeepc, &c))
return -ENODEV;
- rv = parse_arg(buf, count, &value);
+ rv = parse_arg(buf, &value);
if (rv < 0)
return rv;
- if (!rv || value < 0 || value >= c.num)
+ if (value < 0 || value >= c.num)
return -EINVAL;
set_acpi(eeepc, CM_ASL_CPUFV, value);
- return rv;
+ return count;
}

static ssize_t show_cpufv_disabled(struct device *dev,
@@ -402,7 +401,7 @@ static ssize_t store_cpufv_disabled(struct device *dev,
struct eeepc_laptop *eeepc = dev_get_drvdata(dev);
int rv, value;

- rv = parse_arg(buf, count, &value);
+ rv = parse_arg(buf, &value);
if (rv < 0)
return rv;

@@ -412,7 +411,7 @@ static ssize_t store_cpufv_disabled(struct device *dev,
pr_warn("cpufv enabled (not officially supported "
"on this model)\n");
eeepc->cpufv_disabled = false;
- return rv;
+ return count;
case 1:
return -EPERM;
default:
@@ -1042,10 +1041,11 @@ static ssize_t store_sys_hwmon(void (*set)(int), const char *buf, size_t count)
{
int rv, value;

- rv = parse_arg(buf, count, &value);
- if (rv > 0)
- set(value);
- return rv;
+ rv = parse_arg(buf, &value);
+ if (rv < 0)
+ return rv;
+ set(value);
+ return count;
}

static ssize_t show_sys_hwmon(int (*get)(void), char *buf)
--
1.9.3