Re: [PATCH v6 3/3] hwmon: (adt7475) Add support for configuring initial PWM state

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On 22/07/24 15:53, Guenter Roeck wrote:
On 7/21/24 17:58, Chris Packham wrote:
By default the PWM duty cycle in hardware is 100%. On some systems this
can cause unwanted fan noise. Add the ability to specify the fan
connections and initial state of the PWMs via device properties.

Signed-off-by: Chris Packham <chris.packham@xxxxxxxxxxxxxxxxxxx>
---

Notes:
     Changes in v6:
     - Use do_div() instead of plain /
     - Use a helper function to avoid repetition between the of and non-of
       code paths.
     Changes in v5:
     - Deal with PWM frequency and duty cycle being specified in nanoseconds
     Changes in v4:
     - Support DT and ACPI fwnodes
     - Put PWM into manual mode
     Changes in v3:
     - Use the pwm provider/consumer bindings
     Changes in v2:
     - Use correct device property string for frequency
     - Allow -EINVAL and only warn on error
     - Use a frequency of 0 to indicate that the hardware should be left as-is

  drivers/hwmon/adt7475.c | 130 ++++++++++++++++++++++++++++++++++++++++
  1 file changed, 130 insertions(+)

diff --git a/drivers/hwmon/adt7475.c b/drivers/hwmon/adt7475.c
index 4224ffb30483..fc5605d34f36 100644
--- a/drivers/hwmon/adt7475.c
+++ b/drivers/hwmon/adt7475.c
@@ -21,6 +21,8 @@
  #include <linux/of.h>
  #include <linux/util_macros.h>
  +#include <dt-bindings/pwm/pwm.h>
+
  /* Indexes for the sysfs hooks */
    #define INPUT        0
@@ -1662,6 +1664,130 @@ static int adt7475_set_pwm_polarity(struct i2c_client *client)
      return 0;
  }
  +struct adt7475_pwm_config {
+    int index;
+    int freq;
+    int flags;
+    int duty;
+};
+
+static int _adt7475_pwm_properties_parse_args(u32 args[4], struct adt7475_pwm_config *cfg)
+{
+    unsigned long freq_hz;
+    unsigned long duty;
+
+    if (args[1] == 0)
+        return -EINVAL;
+
+    freq_hz = 1000000000UL;
+    do_div(freq_hz, args[1]);
+    duty = 255 * args[3];
+    do_div(duty, args[1]);
+

Gues I am a bit at loss here, just as 0-day. Why use do_div ? It is only needed
for 64-bit divide operations.

Mainly because of Uwe's comment on v5. I think I've avoided the original u64 issue now that I'm converting fwnode_reference_args::args to a u32 array. I can probably get away with plain division, although 255 * args[3] / args[1] might overflow in theory but shouldn't in practice.

I'll let the earth turn and send out a v7 that uses plain division unless someone has a strong opinion that I should sprinkle some more u64s around.


Thanks,
Guenter






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