Date:   Sun, 29 Aug 2021 19:10:32 +1200
From:   Luke Jones <luke@...nes.dev>
To:     Barnabás Pőcze <pobrn@...tonmail.com>
Cc:     linux-kernel@...r.kernel.org, hdegoede@...hat.com,
        hadess@...ess.net, platform-driver-x86@...r.kernel.org,
        Guenter Roeck <linux@...ck-us.net>
Subject: Re: [PATCH v5] asus-wmi: Add support for custom fan curves

Thanks heaps Barnabás, I think I've gotten a very good improvement 
with your help. Let's see how V6 fairs.

On Sat, Aug 28 2021 at 14:39:40 +0000, Barnabás Pőcze 
<pobrn@...tonmail.com> wrote:
> Hi
> 
> 
> 2021. augusztus 28., szombat 8:56 keltezéssel, Luke Jones írta:
>>  [...]
>>  >>  +/*
>>  >>  + * The expected input is of the format
>>  >>  + *     "30:1,49:2,59:3,69:4,79:31,89:49,99:56,109:58"
>>  >>  + * where a pair is 30:1, with 30 = temperature, and 1 = 
>> percentage
>>  >>  +*/
>>  >>  +static int fan_curve_write(struct asus_wmi *asus, u32 dev, char
>>  >> *curve)
>>  >>  +{
>>  >>  +    char * buf, *set, *pair_tmp, *pair, *set_end, *pair_end;
>>  >>  +    int err, ret;
>>  >>  +
>>  >>  +	char *set_delimiter = ",";
>>  >>  +	char *pair_delimiter = ":";
>>  >>  +	bool half_complete = false;
>>  >>  +	bool pair_start = true;
>>  >>  +	u32 prev_percent = 0;
>>  >>  +	u32 prev_temp = 0;
>>  >>  +	u32 percent = 0;
>>  >>  +	u32 shift = 0;
>>  >>  +	u32 temp = 0;
>>  >>  +    u32 arg1 = 0;
>>  >>  +    u32 arg2 = 0;
>>  >>  +    u32 arg3 = 0;
>>  >>  +    u32 arg4 = 0;
>>  >>  +
>>  >>  +    buf = set_end = pair_end = kstrdup(curve, GFP_KERNEL);
>>  >>  +
>>  >>  +	while( (set = strsep(&set_end, set_delimiter)) != NULL ) {
>>  >>  +		pair_tmp = kstrdup(set, GFP_KERNEL);
>>  >>  +        pair_start = true;
>>  >>  +		while( (pair = strsep(&pair_tmp, pair_delimiter)) != NULL ) {
>>  >>  +			err = kstrtouint(pair, 10, &ret);
>>  >>  +            if (err) {
>>  >>  +                kfree(pair_tmp);
>>  >>  +                kfree(buf);
>>  >>  +                return err;
>>  >>  +            }
>>  >>  +
>>  >>  +            if (pair_start) {
>>  >>  +                temp = ret;
>>  >>  +                pair_start = false;
>>  >>  +            } else {
>>  >>  +                percent = ret;
>>  >>  +            }
>>  >>  +		}
>>  >>  +		kfree(pair_tmp);
>>  >>  +
>>  >>  +		if (temp < prev_temp || percent < prev_percent || percent > 
>> 100)
>>  >> {
>>  >>  +            pr_info("Fan curve invalid");
>>  >>  +			pr_info("A value is sequentially lower or percentage is > 
>> 100");
>>  >>  +            kfree(buf);
>>  >>  +            return -EINVAL;
>>  >>  +        }
>>  >>  +
>>  >>  +        prev_temp = temp;
>>  >>  +        prev_percent = percent;
>>  >>  +
>>  >>  +        if (!half_complete) {
>>  >>  +            arg1 += temp << shift;
>>  >>  +            arg3 += percent << shift;
>>  >>  +        } else {
>>  >>  +            arg2 += temp << shift;
>>  >>  +            arg4 += percent << shift;
>>  >>  +        }
>>  >
>>  > As far as I see using 64-bit integers would avoid the need for
>>  > `half_complete`, et al.
>> 
>>  Reworked all that as part of the u8-array stuff. Look forward to 
>> seeing
>>  what you think.
>> 
>>  >
>>  >
>>  >>  +        shift += 8;
>>  >>  +
>>  >>  +        if (shift == 32) {
>>  >>  +            shift = 0;
>>  >>  +            half_complete = true;
>>  >>  +        }
>>  >>  +	}
>>  >>  +	kfree(buf);
>>  >>  +
>>  >
>>  > If you don't insist on using commas, I think it is much simpler to
>>  > parse it using `sscanf()`, e.g.:
>>  >
>>  >   unsigned int temp, prct;
>>  >   int at = 0, len;
>>  >
>>  >   while (sscanf(&buf[at], "%u:%u %n", &temp, &prct, &len) == 2) {
>>  >     /* process `temp` and `prct` */
>>  >
>>  >     at += len;
>>  >   }
>>  >
>>  >   if (buf[at] != '\0')
>>  >     /* error */;
>>  >
>>  > This also has the advantage that you don't need dynamic memory
>>  > allocation.
>> 
>>  Half the reason I did it in the format of 10:20,30:40,.. is to keep
>>  close to a format that many people using some external tools for fan
>>  curves (using acpi_call modue!) are using. I'm open to improvements 
>> ofc.
>> 
> 
> If you don't insist on *requiring* commas, then I think the following 
> works:
> 
>   while (sscanf(&buf[at], "%u:%u %n", &temp, &prct, &len) == 2) {
>     /* process `temp` and `prct` */
> 
>     at += len;
>     at += strspn(&buf[at], ",");
>   }
> 
> But please, whatever parser you end up submitting, make sure it is 
> thoroughly tested.
> 
> 
>>  [...]
>>  >>  +static ssize_t gpu_fan_curve_quiet_show(struct device *dev,
>>  >>  +				   struct device_attribute *attr, char *buf)
>>  >>  +{
>>  >>  +	struct asus_wmi *asus = dev_get_drvdata(dev);
>>  >>  +	return scnprintf(buf, PAGE_SIZE, "%s", 
>> asus->gpu_fan_curve.quiet);
>>  >>  +}
>>  >>  +
>>  >>  +static ssize_t gpu_fan_curve_quiet_store(struct device *dev,
>>  >>  +				    struct device_attribute *attr,
>>  >>  +				    const char *buf, size_t count)
>>  >>  +{
>>  >>  +    struct asus_wmi *asus = dev_get_drvdata(dev);
>>  >>  +    return fan_curve_store(asus, buf, count,
>>  >> ASUS_WMI_DEVID_GPU_FAN_CURVE,
>>  >>  +							&asus->gpu_fan_curve.quiet,
>>  >>  +							asus->gpu_fan_curve.quiet_default);
>>  >>  +}
>>  >>  +
>>  >>  +static DEVICE_ATTR_RW(gpu_fan_curve_quiet);
>>  >
>>  > Even though it is a hwmon thing, I think `SENSOR_ATTR_2()` (from
>>  > linux/hwmon-sysfs.h)
>>  > would be very useful here as you'd avoid creating n+1 functions, 
>> e.g:
>>  >
>>  >   static ssize_t fan_curve_show(struct device *dev, struct
>>  > device_attribute *attr, char *buf)
>>  >   {
>>  >     struct sensor_device_attribute_2 *sattr =
>>  > to_sensor_dev_attr_2(attr);
>>  >     struct asus_wmi *asus = dev_get_drvdata(dev);
>>  >
>>  >     /*
>>  >      * if you stored fan curves in an array, you could then access
>>  > the fan
>>  >      * curve in `asus->fans[sattr->index].curves[sattr->nr]`
>>  >      * /
>>  >   }
>>  >
>>  >   static SENSOR_DEVICE_ATTR_2(some_name1, 0644, fan_curve_show,
>>  > fan_curve_store,
>>  >                               FAN_CPU /* index in the "fans" 
>> array */,
>>  >                               ASUS_THROTTLE_THERMAL_POLICY_SILENT 
>> /*
>>  > index in the "curves" array */);
>>  >
>> 
>>  I'm sorry I don't really understand how this works. Is there a good 
>> doc
>>  for it anywhere? Being unfamiliar with C makes it look a little more
>>  intimidating than what I've managed to do so far.
>> 
> 
> I am not sure, you can find some uses among hwmon drivers.
> 
> If you look into linux/hwmon-sysfs.h, then you can see that 
> `SENSOR_DEVICE_ATTR_2()`
> defines and initializes a `struct sensor_device_attribute_2` object:
> 
>   struct sensor_device_attribute_2 {
>     struct device_attribute dev_attr;
>     u8 index;
>     u8 nr;
>   };
> 
> So it has a normal device attribute inside it, and two extra pieces 
> of data.
> One difference is that when you create the `struct attribute` array
> (`platform_attributes`), then you will need to use 
> `&some_name1.dev_attr.attr`.
> 
> And the idea here is that the show/store callbacks receive a pointer 
> to the
> device attribute that is being read/written, and we know for a fact, 
> that this
> device attribute is inside a `sensor_device_attribute_2` struct. And 
> thus we can
> use the `to_sensor_dev_attr_2()` macro to get a pointer to the "outer"
> `sensor_device_attribute_2` struct that contains the 
> `device_attribute` struct
> that we have a pointer to.
> 
> So now the `index` and `nr` members of that struct can be accessed. 
> You could
> store the index of the fan (e.g. 0 for CPU, 1 for GPU) in `index`, 
> and the profile
> in `nr`. The `ASUS_THROTTLE_THERMAL_POLICY_*` macros go from 0 to 2, 
> so I think
> those would be perfect candidates for the curve index. That's why I 
> used
> `ASUS_THROTTLE_THERMAL_POLICY_SILENT` in the example.
> 
> The fan curve associated with the attribute can now be
> accessed in `asus->fans[sattr->index].curves[sattr->nr]`.
> 
> `to_sensor_dev_attr_2()` is just a wrapper around `container_of()`, 
> so if you're
> familiar with the idea behind that, this shouldn't be too hard to 
> wrap your
> head around.
> 
>   #define to_sensor_dev_attr_2(_dev_attr) \
>     container_of(_dev_attr, struct sensor_device_attribute_2, 
> dev_attr)
> 
> What it does, is that if you give it a pointer to the `dev_attr` 
> member of a
> `struct sensor_device_attribute_2`, then it'll give you back a pointer
> to the `struct sensor_device_attribute_2`. `container_of()` basically 
> does a
> "conversion" from pointer-to-member-of-struct-X to 
> pointer-to-struct-X.
> 
> In some sense, you might think of `struct device_attribute` as the 
> "base class",
> and the `struct sensor_device_attribute_2` as the "derived class" 
> here. And what
> `to_sensor_dev_attr_2()` is a down-cast from the base class to the 
> derived,
> e.g. something like this in C++:
> 
>   struct device_attribute { ... };
>   struct sensor_device_attribute_2 : device_attribute {
>     u8 index;
>     u8 nr;
>   };
> 
>   /* `device_attr` is of type `struct device_attribute *` */
>   static_cast<sensor_device_attribute_2 *>(device_attr);
>   /* there's also dynamic_cast which can do the same down-cast,
>      but it does runtime type checking as well */
>   /* both of the mentioned C++ casts check if the pointer is nullptr,
>      normal container_of() does not that, but there is 
> container_of_safe() */
> 
> It may be too detailed, I'm not sure; please let me know if you have 
> other questions.
> 
> 
>>  [...]
> 
> 
> Best regards,
> Barnabás Pőcze

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