Messages in this thread | | | Date | Sat, 28 Nov 2015 09:28:40 +0100 | From | Jacek Anaszewski <> | Subject | Re: [PATCH v2 8/9] leds: add LM3633 driver |
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On 11/27/2015 12:19 PM, Jacek Anaszewski wrote: > Hi Milo, > > Thanks for the update. I have few comments below. > [...] >> +static u8 lm3633_led_scale_max_brightness(struct ti_lmu_led *lmu_led, >> u32 imax) >> +{ >> + u8 max_current = lm3633_led_convert_current_to_index(imax); >> + const u8 max_brightness_table[] = { >> + [LMU_IMAX_5mA] = 191, >> + [LMU_IMAX_6mA] = 197, >> + [LMU_IMAX_7mA] = 203, >> + [LMU_IMAX_8mA] = 208, >> + [LMU_IMAX_9mA] = 212, >> + [LMU_IMAX_10mA] = 216, >> + [LMU_IMAX_11mA] = 219, >> + [LMU_IMAX_12mA] = 222, >> + [LMU_IMAX_13mA] = 225, >> + [LMU_IMAX_14mA] = 228, >> + [LMU_IMAX_15mA] = 230, >> + [LMU_IMAX_16mA] = 233, >> + [LMU_IMAX_17mA] = 235, >> + [LMU_IMAX_18mA] = 237, >> + [LMU_IMAX_19mA] = 239, >> + [LMU_IMAX_20mA] = 241, >> + [LMU_IMAX_21mA] = 242, >> + [LMU_IMAX_22mA] = 244, >> + [LMU_IMAX_23mA] = 246, >> + [LMU_IMAX_24mA] = 247, >> + [LMU_IMAX_25mA] = 249, >> + [LMU_IMAX_26mA] = 250, >> + [LMU_IMAX_27mA] = 251, >> + [LMU_IMAX_28mA] = 253, >> + [LMU_IMAX_29mA] = 254, >> + [LMU_IMAX_30mA] = 255, >> + }; > > After analyzing the subject one more time I think that we need to > change the approach regarding max brightness issue. > > At first - we shouldn't fix max current to max possible register value. > Instead we should take led-max-microamp property and write its value > to the [0x22 + bank offset] registers.
It was of course a mental shortcut. The value to write should be calculated by transforming the formula given next to the register documentation:
11111 = 29.8 mA 0.8mA steps, FS = 5mA + code * 0.8 mA
code is here the [0x22 + bank_offset] register value.
Effectively, the formula to calculate the register value basing on led-max-microamp value should be:
FS = led-max-microamp - 5000 / 800
E.g. for 20.2 mA:
FS = (20200 - 5000) / 800 = 19
for 29.8 mA:
FS = (29800 - 5000) / 800 = 31
for 5 mA:
FS = (5000 - 5000) / 800 = 0
From the above min, max and step values for led-max-microamp are 5000, 29800 and 800 respectively. Please correct DT documentation accordingly.
> With this approach whole 0-255 range of brightness levels will be > valid for the driver. > > In effect all LMU_IMAX* enums seem to be not needed.
-- Best Regards, Jacek Anaszewski
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