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SubjectRe: [PATCH] ARM: dts: rockchip: Use interpolated brightness tables for veyron
Hi,

On Tue, Oct 1, 2019 at 4:07 PM Matthias Kaehlcke <mka@chromium.org> wrote:
> --- a/arch/arm/boot/dts/rk3288-veyron-minnie.dts
> +++ b/arch/arm/boot/dts/rk3288-veyron-minnie.dts
> @@ -39,39 +39,8 @@
>
> &backlight {
> /* Minnie panel PWM must be >= 1%, so start non-zero brightness at 3 */
> - brightness-levels = <
> - 0 3 4 5 6 7
> - 8 9 10 11 12 13 14 15
> - 16 17 18 19 20 21 22 23
> - 24 25 26 27 28 29 30 31
> - 32 33 34 35 36 37 38 39
> - 40 41 42 43 44 45 46 47
> - 48 49 50 51 52 53 54 55
> - 56 57 58 59 60 61 62 63
> - 64 65 66 67 68 69 70 71
> - 72 73 74 75 76 77 78 79
> - 80 81 82 83 84 85 86 87
> - 88 89 90 91 92 93 94 95
> - 96 97 98 99 100 101 102 103
> - 104 105 106 107 108 109 110 111
> - 112 113 114 115 116 117 118 119
> - 120 121 122 123 124 125 126 127
> - 128 129 130 131 132 133 134 135
> - 136 137 138 139 140 141 142 143
> - 144 145 146 147 148 149 150 151
> - 152 153 154 155 156 157 158 159
> - 160 161 162 163 164 165 166 167
> - 168 169 170 171 172 173 174 175
> - 176 177 178 179 180 181 182 183
> - 184 185 186 187 188 189 190 191
> - 192 193 194 195 196 197 198 199
> - 200 201 202 203 204 205 206 207
> - 208 209 210 211 212 213 214 215
> - 216 217 218 219 220 221 222 223
> - 224 225 226 227 228 229 230 231
> - 232 233 234 235 236 237 238 239
> - 240 241 242 243 244 245 246 247
> - 248 249 250 251 252 253 254 255>;
> + brightness-levels = <3 255>;
> + num-interpolated-steps = <251>;

I _think_ you want:

brightness-levels = <0 3 255>;
num-interpolated-steps = <252>;

Specifically:

* It seems like you're intending to keep everything the same and just
have a more compact representation, right? Looking through the values
in '/sys/class/backlight/backlight' on minnie shows differences before
and after your patch.

* I think you want brightness of 0 to match to PWM level 0.

* If I put in printouts in the code with your table, I see:

pwm-backlight backlight: new number of brightness levels: 252
pwm-backlight backlight: i=0, j=0, lc=0, value=3
pwm-backlight backlight: i=0, j=1, lc=1, value=4
...
pwm-backlight backlight: i=0, j=250, lc=250, value=253
pwm-backlight backlight: lc=251, data->levels[i]=255

...as you can see, you end up missing assigning a value of 254.


-Doug

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