Message ID | 20240711234614.3104839-1-chris.packham@alliedtelesis.co.nz |
---|---|
Headers | show |
Series | hwmon: (adt7475) duty cycle configuration | expand |
On 7/11/24 16:46, 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@alliedtelesis.co.nz> > --- ... > +static int adt7475_pwm_properties_parse_reference_args(struct fwnode_handle *fwnode, > + struct adt7475_pwm_config *cfg) > +{ > + int ret; > + struct fwnode_reference_args args = {}; > + int freq_hz; > + int duty; > + > + ret = fwnode_property_get_reference_args(fwnode, "pwms", "#pwm-cells", 0, 0, &args); > + if (ret) > + return ret; > + > + if (args.nargs != 4) { > + fwnode_handle_put(args.fwnode); > + return -EINVAL; > + } > + > + freq_hz = 1000000000UL / args.args[1]; > + duty = 255 / (args.args[1] / args.args[3]); > + You'll need to validate args.args[1] and args.args[3] to ensure that there are no divide by 0 errors. On a side note, a = b / (c / d) == b / c * d (at least for d != 0) Since the result is defined for d == 0, you'd only have to make sure that args.args[1] > 0 and that the result for the duty cycle is <= 255. > + cfg->index = args.args[0]; > + cfg->freq = find_closest(freq_hz, pwmfreq_table, ARRAY_SIZE(pwmfreq_table)); > + cfg->flags = args.args[2]; > + cfg->duty = clamp_val(duty, 0, 0xFF); > + > + fwnode_handle_put(args.fwnode); > + > + return 0; > +} > + > +static int adt7475_pwm_properties_parse_args(struct fwnode_handle *fwnode, > + struct adt7475_pwm_config *cfg) > +{ > + int ret; > + u32 args[4] = {}; > + int freq_hz; > + int duty; > + > + ret = fwnode_property_read_u32_array(fwnode, "pwms", args, ARRAY_SIZE(args)); > + if (ret) > + return ret; > + > + freq_hz = 1000000000UL / args[1]; > + duty = 255 / (args[1] / args[3]); > + > + cfg->index = args[0]; > + cfg->freq = find_closest(freq_hz, pwmfreq_table, ARRAY_SIZE(pwmfreq_table)); > + cfg->flags = args[2]; > + cfg->duty = clamp_val(duty, 0, 0xFF); > + The code above is duplicate; please combine into a single function (I don't mind if it has four parameters). Thanks, Guenter
On Thu, Jul 11, 2024 at 09:37:29PM -0700, Guenter Roeck wrote: > On 7/11/24 16:46, 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@alliedtelesis.co.nz> > > --- > ... > > +static int adt7475_pwm_properties_parse_reference_args(struct fwnode_handle *fwnode, > > + struct adt7475_pwm_config *cfg) > > +{ > > + int ret; > > + struct fwnode_reference_args args = {}; > > + int freq_hz; > > + int duty; > > + > > + ret = fwnode_property_get_reference_args(fwnode, "pwms", "#pwm-cells", 0, 0, &args); > > + if (ret) > > + return ret; > > + > > + if (args.nargs != 4) { > > + fwnode_handle_put(args.fwnode); > > + return -EINVAL; > > + } > > + > > + freq_hz = 1000000000UL / args.args[1]; > > + duty = 255 / (args.args[1] / args.args[3]); > > + > You'll need to validate args.args[1] and args.args[3] to ensure that there are no > divide by 0 errors. > > On a side note, > a = b / (c / d) == b / c * d (at least for d != 0) > Since the result is defined for d == 0, you'd only have to make sure > that args.args[1] > 0 and that the result for the duty cycle is <= 255. On a side side note: Depending on the actual values it might be beneficial to use b * d / c instead. b * d might overflow, but in other cases (e.g. b = 7, c = 8, d = 8) the resulting precision is much better. Best regards Uwe