Messages in this thread | | | Date | Wed, 2 Oct 2019 16:44:36 -0700 | From | Matthias Kaehlcke <> | Subject | Re: [PATCH] ARM: dts: rockchip: Use interpolated brightness tables for veyron |
| |
On Wed, Oct 02, 2019 at 03:23:54PM -0700, Doug Anderson wrote: > 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?
Ideally yes, I thought we were missing 1 level due to the 0 step being missing, but it's actually 2, since I interpreted 'num-interpolated-steps' as the number between two values in the table, however it is this number +1.
> 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.
For level 0 that was actually given, due to
pwm_backlight_update_status() { .. if (brightness > 0) { ... } else pwm_backlight_power_off(pb); ... }
but we're slightly off for the rest of the levels.
> * 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.
Thanks for investigating. With 'num-interpolated-steps' increased by one this is fixed, though we are still missing one level at the beginning of the table. I didn't expect 'brightness-levels = <0 3 255>' to work, since there are less than 252/251 integer numbers between 0 and 3, but the code actually accounts for that case and just interprets it as a single step, which is what we want.
Long story short: you are right, we want
brightness-levels = <0 3 255>; num-interpolated-steps = <252>;
| |