diff mbox

Intel-kms in Linux-4.2rc causes regression due to dithering always on.

Message ID 55CA9464.3030204@gmail.com (mailing list archive)
State New, archived
Headers show

Commit Message

Mario Kleiner Aug. 12, 2015, 12:33 a.m. UTC 
On 08/07/2015 09:14 AM, Daniel Vetter wrote:
> On Fri, Aug 07, 2015 at 12:45:52AM +0200, Mario Kleiner wrote:
>> On 08/07/2015 12:12 AM, Daniel Vetter wrote:
>>> On Thu, Aug 6, 2015 at 11:56 PM, Mario Kleiner
>>> <mario.kleiner.de@gmail.com> wrote:
>>>> Hi Daniel and all,
>>>>
>>>> since Linux 4.2 (tested with rc4), i think this commit
>>>> d328c9d78d64ca11e744fe227096990430a88477
>>>> "drm/i915: Select starting pipe bpp irrespective or the primary plane"
>>>>
>>>> causes trouble for me and my users, as tested on Intel HD Ironlake and Ivy
>>>> Bridge with MiniDP->Singlelink-DVI adapter -> Measurement device.
>>>>
>>>> Afaics it causes dithering to always be enabled on a regular 8bpc
>>>> framebuffer, even when outputting to a 8 bpc DVI-D output, and that
>>>> dithering causes my display measurement equipment and other special display
>>>> devices used for neuro-science and medical applications to fail. This
>>>> equipment requires an identity passthrough of 8 bpc framebuffer pixels to
>>>> the digital outputs, iow. dithering off.
>>>>
>>>> Log output on Linux 4.1 (good):
>>>>
>>>> Aug  1 06:39:26 twisty kernel: [  154.175394]
>>>> [drm:connected_sink_compute_bpp] [CONNECTOR:35:HDMI-A-1] checking for sink
>>>> bpp constrains
>>>> Aug  1 06:39:26 twisty kernel: [  154.175396]
>>>> [drm:intel_hdmi_compute_config] picking bpc to 8 for HDMI output
>>>> Aug  1 06:39:26 twisty kernel: [  154.175397]
>>>> [drm:intel_hdmi_compute_config] forcing pipe bpc to 24 for HDMI
>>>> Aug  1 06:39:26 twisty kernel: [  154.175400] [drm:ironlake_check_fdi_lanes]
>>>> checking fdi config on pipe A, lanes 1
>>>> Aug  1 06:39:26 twisty kernel: [  154.175402]
>>>> [drm:intel_modeset_pipe_config] plane bpp: 24, pipe bpp: 24, dithering: 0
>>>> Aug  1 06:39:26 twisty kernel: [  154.175403] [drm:intel_dump_pipe_config]
>>>> [CRTC:20][modeset] config for pipe A
>>>> Aug  1 06:39:26 twisty kernel: [  154.175404] [drm:intel_dump_pipe_config]
>>>> cpu_transcoder: A
>>>> Aug  1 06:39:26 twisty kernel: [  154.175405] [drm:intel_dump_pipe_config]
>>>> pipe bpp: 24, dithering: 0
>>>>
>>>> Log output on Linux 4.2-rc4 (bad):
>>>>
>>>> Aug  1 06:21:31 twisty kernel: [  200.924831]
>>>> [drm:connected_sink_compute_bpp] [CONNECTOR:36:HDMI-A-1] checking for sink
>>>> bpp constrains
>>>> Aug  1 06:21:31 twisty kernel: [  200.924832]
>>>> [drm:connected_sink_compute_bpp] clamping display bpp (was 36) to default
>>>> limit of 24
>>>> Aug  1 06:21:31 twisty kernel: [  200.924834]
>>>> [drm:intel_hdmi_compute_config] picking bpc to 8 for HDMI output
>>>> Aug  1 06:21:31 twisty kernel: [  200.924835]
>>>> [drm:intel_hdmi_compute_config] forcing pipe bpc to 24 for HDMI
>>>> Aug  1 06:21:31 twisty kernel: [  200.924838] [drm:ironlake_check_fdi_lanes]
>>>> checking fdi config on pipe A, lanes 1
>>>> Aug  1 06:21:31 twisty kernel: [  200.924840]
>>>> [drm:intel_modeset_pipe_config] plane bpp: 36, pipe bpp: 24, dithering: 1
>>>> Aug  1 06:21:31 twisty kernel: [  200.924841] [drm:intel_dump_pipe_config]
>>>> [CRTC:21][modeset] config ffff880131a5c800 for pipe A
>>>> Aug  1 06:21:31 twisty kernel: [  200.924842] [drm:intel_dump_pipe_config]
>>>> cpu_transcoder: A
>>>> Aug  1 06:21:31 twisty kernel: [  200.924843] [drm:intel_dump_pipe_config]
>>>> pipe bpp: 24, dithering: 1
>>>>
>>>> Ideas what to do about this?
>>>
>>> Well I somehow assumed the dither bit would be sane and not wreak
>>> havoc with the lower bits when they would fit into the final bpc pipe
>>> mode ... Can you confirm with your equipment that we seem to be doing
>>> 8bpc->6bpc dithering on the 8bpc sink?
>>>
>>
>> It will need a bit of work to find this out when i'm back in the lab. So far
>> i just know something bad is happening to the signal and i assume it's the
>> dithering, because the visual error pattern of messiness looks like that
>> caused by dithering. E.g., on a static framebuffer i see some repeating
>> pattern over the screen, but the pattern changes with every OpenGL
>> bufferswap, even if i swap to the same fb content, as if the swap triggers
>> some change of the spatial dither pattern (assuming PIPECONF_DITHER_TYPE_SP
>> = spatial dithering?)
>>
>>> If that's the case we simply limit to only ever dither when the sink
>>> is 6bpc, and not in any other case.
>>> -Daniel
>>>
>>
>> That would be an improvement for my immediate problem if that works. But
>> assuming we have 10 bpc framebuffers at some point, dithering 10 bpc -> 8
>> bpc would also have some practical use.
>>
>> Probably some dynamic check would be good, a la if there is a mismatch
>> between the max(bpc) over all active planes and the supported depth of the
>> sink then dither?
>>
>> It's not clear to me where the dithering happens on intel hw. I'd expected
>> that with a 24 bpp framebuffer feeding into a 24 bpp pipe, dithering simply
>> wouldn't do anything even if enabled.
>
> Yeah my assumption was that if you run the pipe at a given bpc it will
> just pass through anything that fits and only dither the additional bits.
> But obviously that's not how the hardware works ...
>
> The problem with adaptive schemes is that we have multiple planes nowadays
> and they might all run at different depths. And dither seems to be
> happening at the pipe/overall level (at least there's only one bit). Of
> course this wouldn't be a problem if the thing wouldn't mangle bits which
> should pass!
>
> Anyway if we can confirm this I think dithering for only 6bpc should be
> ok.
> -Daniel
>

Ok, did some testing and the results are weird. The procedure was to 
render a fullscreen constant color image via OpenGL - set constant color 
framebuffer via glClearColor + glClear + bufferswap, using pageflips 
through unredirected fullscreen windows. Gamma tables were set to 
identity mapping. I stepped through all 256  R = G = B = Ref. values and 
my equipment captured the actual single-link DVI-D video input signal of 
the topmost scanline. The table below shows the actual value in the 
framebuffer vs. the readback 8 bpc values of the red channel for the 
first 10 pixels in the scanline, green and blue channels have same result:

 >>
 >> On Linux 4.2-rc5, Intel HD Ironlake, 24 bpp fb,pipeconf etc. via DVI-D.

Ref 0: 0 0 0 0 0 0 0 0 0 0
Ref 1: 1 0 1 0 1 0 1 0 1 0
Ref 2: 2 1 2 1 2 1 2 1 2 1
Ref 3: 3 2 3 2 3 2 3 2 3 2
Ref 4: 4 3 4 3 4 3 4 3 4 3
Ref 5: 5 4 5 4 5 4 5 4 5 4
Ref 6: 6 5 6 5 6 5 6 5 6 5
Ref 7: 7 6 7 6 7 6 7 6 7 6
Ref 8: 8 7 8 7 8 7 8 7 8 7
Ref 9: 9 8 9 8 9 8 9 8 9 8
Ref 10: 10 9 10 9 10 9 10 9 10 9
Ref 11: 11 10 11 10 11 10 11 10 11 10
Ref 12: 12 11 12 11 12 11 12 11 12 11
Ref 13: 13 12 13 12 13 12 13 12 13 12
Ref 14: 14 13 14 13 14 13 14 13 14 13
Ref 15: 15 14 15 14 15 14 15 14 15 14
Ref 16: 16 15 16 15 16 15 16 15 16 15
Ref 17: 17 16 17 16 17 16 17 16 17 16
Ref 18: 18 17 18 17 18 17 18 17 18 17
Ref 19: 19 18 19 18 19 18 19 18 19 18
Ref 20: 20 19 20 19 20 19 20 19 20 19
Ref 21: 21 20 21 20 21 20 21 20 21 20
Ref 22: 22 21 22 21 22 21 22 21 22 21
Ref 23: 23 22 23 22 23 22 23 22 23 22
Ref 24: 24 23 24 23 24 23 24 23 24 23
Ref 25: 25 24 25 24 25 24 25 24 25 24
Ref 26: 26 25 26 25 26 25 26 25 26 25
Ref 27: 27 26 27 26 27 26 27 26 27 26
Ref 28: 28 27 28 27 28 27 28 27 28 27
Ref 29: 29 28 29 28 29 28 29 28 29 28
Ref 30: 30 29 30 29 30 29 30 29 30 29
Ref 31: 31 30 31 30 31 30 31 30 31 30
Ref 32: 32 31 32 31 32 31 32 31 32 31
Ref 33: 33 32 33 32 33 32 33 32 33 32
Ref 34: 34 33 34 33 34 33 34 33 34 33
Ref 35: 35 34 35 34 35 34 35 34 35 34
Ref 36: 36 35 36 35 36 35 36 35 36 35
Ref 37: 37 36 37 36 37 36 37 36 37 36
Ref 38: 38 37 38 37 38 37 38 37 38 37
Ref 39: 39 38 39 38 39 38 39 38 39 38
Ref 40: 40 39 40 39 40 39 40 39 40 39
Ref 41: 41 40 41 40 41 40 41 40 41 40
Ref 42: 42 41 42 41 42 41 42 41 42 41
Ref 43: 43 42 43 42 43 42 43 42 43 42
Ref 44: 44 43 44 43 44 43 44 43 44 43
Ref 45: 45 44 45 44 45 44 45 44 45 44
Ref 46: 46 45 46 45 46 45 46 45 46 45
Ref 47: 47 46 47 46 47 46 47 46 47 46
Ref 48: 48 47 48 47 48 47 48 47 48 47
Ref 49: 49 48 49 48 49 48 49 48 49 48
Ref 50: 50 49 50 49 50 49 50 49 50 49
Ref 51: 51 50 51 50 51 50 51 50 51 50
Ref 52: 52 51 52 51 52 51 52 51 52 51
Ref 53: 53 52 53 52 53 52 53 52 53 52
Ref 54: 54 53 54 53 54 53 54 53 54 53
Ref 55: 55 54 55 54 55 54 55 54 55 54
Ref 56: 56 55 56 55 56 55 56 55 56 55
Ref 57: 57 56 57 56 57 56 57 56 57 56
Ref 58: 58 57 58 57 58 57 58 57 58 57
Ref 59: 59 58 59 58 59 58 59 58 59 58
Ref 60: 60 59 60 59 60 59 60 59 60 59
Ref 61: 61 60 61 60 61 60 61 60 61 60
Ref 62: 62 61 62 61 62 61 62 61 62 61
Ref 63: 63 62 63 62 63 62 63 62 63 62
Ref 64: 64 63 64 63 64 63 64 63 64 63
Ref 65: 65 64 65 64 65 64 65 64 65 64
Ref 66: 66 65 66 65 66 65 66 65 66 65
Ref 67: 67 66 67 66 67 66 67 66 67 66
Ref 68: 68 67 68 67 68 67 68 67 68 67
Ref 69: 69 68 69 68 69 68 69 68 69 68
Ref 70: 70 69 70 69 70 69 70 69 70 69
Ref 71: 71 70 71 70 71 70 71 70 71 70
Ref 72: 72 71 72 71 72 71 72 71 72 71
Ref 73: 73 72 73 72 73 72 73 72 73 72
Ref 74: 74 73 74 73 74 73 74 73 74 73
Ref 75: 75 74 75 74 75 74 75 74 75 74
Ref 76: 76 75 76 75 76 75 76 75 76 75
Ref 77: 77 76 77 76 77 76 77 76 77 76
Ref 78: 78 77 78 77 78 77 78 77 78 77
Ref 79: 79 78 79 78 79 78 79 78 79 78
Ref 80: 80 79 80 79 80 79 80 79 80 79
Ref 81: 81 80 81 80 81 80 81 80 81 80
Ref 82: 82 81 82 81 82 81 82 81 82 81
Ref 83: 83 82 83 82 83 82 83 82 83 82
Ref 84: 84 83 84 83 84 83 84 83 84 83
Ref 85: 85 84 85 84 85 84 85 84 85 84
Ref 86: 86 85 86 85 86 85 86 85 86 85
Ref 87: 87 86 87 86 87 86 87 86 87 86
Ref 88: 88 87 88 87 88 87 88 87 88 87
Ref 89: 89 88 89 88 89 88 89 88 89 88
Ref 90: 90 89 90 89 90 89 90 89 90 89
Ref 91: 91 90 91 90 91 90 91 90 91 90
Ref 92: 92 91 92 91 92 91 92 91 92 91
Ref 93: 93 92 93 92 93 92 93 92 93 92
Ref 94: 94 93 94 93 94 93 94 93 94 93
Ref 95: 95 94 95 94 95 94 95 94 95 94
Ref 96: 96 95 96 95 96 95 96 95 96 95
Ref 97: 97 96 97 96 97 96 97 96 97 96
Ref 98: 98 97 98 97 98 97 98 97 98 97
Ref 99: 99 98 99 98 99 98 99 98 99 98
Ref 100: 100 99 100 99 100 99 100 99 100 99
Ref 101: 101 100 101 100 101 100 101 100 101 100
Ref 102: 102 101 102 101 102 101 102 101 102 101
Ref 103: 103 102 103 102 103 102 103 102 103 102
Ref 104: 104 103 104 103 104 103 104 103 104 103
Ref 105: 105 104 105 104 105 104 105 104 105 104
Ref 106: 106 105 106 105 106 105 106 105 106 105
Ref 107: 107 106 107 106 107 106 107 106 107 106
Ref 108: 108 107 108 107 108 107 108 107 108 107
Ref 109: 109 108 109 108 109 108 109 108 109 108
Ref 110: 110 109 110 109 110 109 110 109 110 109
Ref 111: 111 110 111 110 111 110 111 110 111 110
Ref 112: 112 111 112 111 112 111 112 111 112 111
Ref 113: 113 112 113 112 113 112 113 112 113 112
Ref 114: 114 113 114 113 114 113 114 113 114 113
Ref 115: 115 114 115 114 115 114 115 114 115 114
Ref 116: 116 115 116 115 116 115 116 115 116 115
Ref 117: 117 116 117 116 117 116 117 116 117 116
Ref 118: 118 117 118 117 118 117 118 117 118 117
Ref 119: 119 118 119 118 119 118 119 118 119 118
Ref 120: 120 119 120 119 120 119 120 119 120 119
Ref 121: 121 120 121 120 121 120 121 120 121 120
Ref 122: 122 121 122 121 122 121 122 121 122 121
Ref 123: 123 122 123 122 123 122 123 122 123 122
Ref 124: 124 123 124 123 124 123 124 123 124 123
Ref 125: 125 124 125 124 125 124 125 124 125 124
Ref 126: 126 125 126 125 126 125 126 125 126 125
Ref 127: 127 126 127 126 127 126 127 126 127 126
Ref 128: 127 128 127 128 127 128 127 128 127 128
Ref 129: 128 129 128 129 128 129 128 129 128 129
Ref 130: 129 130 129 130 129 130 129 130 129 130
Ref 131: 130 131 130 131 130 131 130 131 130 131
Ref 132: 131 132 131 132 131 132 131 132 131 132
Ref 133: 132 133 132 133 132 133 132 133 132 133
Ref 134: 133 134 133 134 133 134 133 134 133 134
Ref 135: 134 135 134 135 134 135 134 135 134 135
Ref 136: 135 136 135 136 135 136 135 136 135 136
Ref 137: 136 137 136 137 136 137 136 137 136 137
Ref 138: 137 138 137 138 137 138 137 138 137 138
Ref 139: 138 139 138 139 138 139 138 139 138 139
Ref 140: 139 140 139 140 139 140 139 140 139 140
Ref 141: 140 141 140 141 140 141 140 141 140 141
Ref 142: 141 142 141 142 141 142 141 142 141 142
Ref 143: 142 143 142 143 142 143 142 143 142 143
Ref 144: 143 144 143 144 143 144 143 144 143 144
Ref 145: 144 145 144 145 144 145 144 145 144 145
Ref 146: 145 146 145 146 145 146 145 146 145 146
Ref 147: 146 147 146 147 146 147 146 147 146 147
Ref 148: 147 148 147 148 147 148 147 148 147 148
Ref 149: 148 149 148 149 148 149 148 149 148 149
Ref 150: 149 150 149 150 149 150 149 150 149 150
Ref 151: 150 151 150 151 150 151 150 151 150 151
Ref 152: 151 152 151 152 151 152 151 152 151 152
Ref 153: 152 153 152 153 152 153 152 153 152 153
Ref 154: 153 154 153 154 153 154 153 154 153 154
Ref 155: 154 155 154 155 154 155 154 155 154 155
Ref 156: 155 156 155 156 155 156 155 156 155 156
Ref 157: 156 157 156 157 156 157 156 157 156 157
Ref 158: 157 158 157 158 157 158 157 158 157 158
Ref 159: 158 159 158 159 158 159 158 159 158 159
Ref 160: 159 160 159 160 159 160 159 160 159 160
Ref 161: 160 161 160 161 160 161 160 161 160 161
Ref 162: 161 162 161 162 161 162 161 162 161 162
Ref 163: 162 163 162 163 162 163 162 163 162 163
Ref 164: 163 164 163 164 163 164 163 164 163 164
Ref 165: 164 165 164 165 164 165 164 165 164 165
Ref 166: 165 166 165 166 165 166 165 166 165 166
Ref 167: 166 167 166 167 166 167 166 167 166 167
Ref 168: 167 168 167 168 167 168 167 168 167 168
Ref 169: 168 169 168 169 168 169 168 169 168 169
Ref 170: 169 170 169 170 169 170 169 170 169 170
Ref 171: 170 171 170 171 170 171 170 171 170 171
Ref 172: 171 172 171 172 171 172 171 172 171 172
Ref 173: 172 173 172 173 172 173 172 173 172 173
Ref 174: 173 174 173 174 173 174 173 174 173 174
Ref 175: 174 175 174 175 174 175 174 175 174 175
Ref 176: 175 176 175 176 175 176 175 176 175 176
Ref 177: 176 177 176 177 176 177 176 177 176 177
Ref 178: 177 178 177 178 177 178 177 178 177 178
Ref 179: 178 179 178 179 178 179 178 179 178 179
Ref 180: 179 180 179 180 179 180 179 180 179 180
Ref 181: 180 181 180 181 180 181 180 181 180 181
Ref 182: 181 182 181 182 181 182 181 182 181 182
Ref 183: 182 183 182 183 182 183 182 183 182 183
Ref 184: 183 184 183 184 183 184 183 184 183 184
Ref 185: 184 185 184 185 184 185 184 185 184 185
Ref 186: 185 186 185 186 185 186 185 186 185 186
Ref 187: 186 187 186 187 186 187 186 187 186 187
Ref 188: 187 188 187 188 187 188 187 188 187 188
Ref 189: 188 189 188 189 188 189 188 189 188 189
Ref 190: 189 190 189 190 189 190 189 190 189 190
Ref 191: 190 191 190 191 190 191 190 191 190 191
Ref 192: 192 192 192 192 192 192 192 192 192 192
Ref 193: 193 193 193 193 193 193 193 193 193 193
Ref 194: 194 194 194 194 194 194 194 194 194 194
Ref 195: 195 195 195 195 195 195 195 195 195 195
Ref 196: 196 196 196 196 196 196 196 196 196 196
Ref 197: 197 197 197 197 197 197 197 197 197 197
Ref 198: 198 198 198 198 198 198 198 198 198 198
Ref 199: 199 199 199 199 199 199 199 199 199 199
Ref 200: 200 200 200 200 200 200 200 200 200 200
Ref 201: 201 201 201 201 201 201 201 201 201 201
Ref 202: 202 202 202 202 202 202 202 202 202 202
Ref 203: 203 203 203 203 203 203 203 203 203 203
Ref 204: 204 204 204 204 204 204 204 204 204 204
Ref 205: 205 205 205 205 205 205 205 205 205 205
Ref 206: 206 206 206 206 206 206 206 206 206 206
Ref 207: 207 207 207 207 207 207 207 207 207 207
Ref 208: 208 208 208 208 208 208 208 208 208 208
Ref 209: 209 209 209 209 209 209 209 209 209 209
Ref 210: 210 210 210 210 210 210 210 210 210 210
Ref 211: 211 211 211 211 211 211 211 211 211 211
Ref 212: 212 212 212 212 212 212 212 212 212 212
Ref 213: 213 213 213 213 213 213 213 213 213 213
Ref 214: 214 214 214 214 214 214 214 214 214 214
Ref 215: 215 215 215 215 215 215 215 215 215 215
Ref 216: 216 216 216 216 216 216 216 216 216 216
Ref 217: 217 217 217 217 217 217 217 217 217 217
Ref 218: 218 218 218 218 218 218 218 218 218 218
Ref 219: 219 219 219 219 219 219 219 219 219 219
Ref 220: 220 220 220 220 220 220 220 220 220 220
Ref 221: 221 221 221 221 221 221 221 221 221 221
Ref 222: 222 222 222 222 222 222 222 222 222 222
Ref 223: 223 223 223 223 223 223 223 223 223 223
Ref 224: 224 224 224 224 224 224 224 224 224 224
Ref 225: 225 225 225 225 225 225 225 225 225 225
Ref 226: 226 226 226 226 226 226 226 226 226 226
Ref 227: 227 227 227 227 227 227 227 227 227 227
Ref 228: 228 228 228 228 228 228 228 228 228 228
Ref 229: 229 229 229 229 229 229 229 229 229 229
Ref 230: 230 230 230 230 230 230 230 230 230 230
Ref 231: 231 231 231 231 231 231 231 231 231 231
Ref 232: 232 232 232 232 232 232 232 232 232 232
Ref 233: 233 233 233 233 233 233 233 233 233 233
Ref 234: 234 234 234 234 234 234 234 234 234 234
Ref 235: 235 235 235 235 235 235 235 235 235 235
Ref 236: 236 236 236 236 236 236 236 236 236 236
Ref 237: 237 237 237 237 237 237 237 237 237 237
Ref 238: 238 238 238 238 238 238 238 238 238 238
Ref 239: 239 239 239 239 239 239 239 239 239 239
Ref 240: 240 240 240 240 240 240 240 240 240 240
Ref 241: 241 241 241 241 241 241 241 241 241 241
Ref 242: 242 242 242 242 242 242 242 242 242 242
Ref 243: 243 243 243 243 243 243 243 243 243 243
Ref 244: 244 244 244 244 244 244 244 244 244 244
Ref 245: 245 245 245 245 245 245 245 245 245 245
Ref 246: 246 246 246 246 246 246 246 246 246 246
Ref 247: 247 247 247 247 247 247 247 247 247 247
Ref 248: 248 248 248 248 248 248 248 248 248 248
Ref 249: 249 249 249 249 249 249 249 249 249 249
Ref 250: 250 250 250 250 250 250 250 250 250 250
Ref 251: 251 251 251 251 251 251 251 251 251 251
Ref 252: 252 252 252 252 252 252 252 252 252 252
Ref 253: 253 253 253 253 253 253 253 253 253 253
Ref 254: 254 254 254 254 254 254 254 254 254 254
Ref 255: 255 255 255 255 255 255 255 255 255 255

I get the same result on Ironlake and IvyBridge. So it's not dithering 
the 8 bpc fb on the 8 bpc pipe to 6 bpc output, as all 256 values are in 
the output, but it is somehow screwing with the 8 bpc signal for no 
reason. Values >= 192 are unaffected, values between 0 and 127 get 
treated slightly different wrong than between 128 and 191.

On Linux <= 4.1 the output is as expected. If i apply this patch to 
force dithering off, then the problem is fixed on 4.2-rc:

         if (intel_crtc->config->base.adjusted_mode.flags & 
DRM_MODE_FLAG_INTERLACE)
                 val |= PIPECONF_INTERLACED_ILK;

So the weirdness is triggered by dither enable on a 24 bpp fb feeding 
into the 24 bpp pipe, at least on the ironlake code path. Don't have a 
haswell part atm. to test that.

-mario
diff mbox

Patch

--- a/drivers/gpu/drm/i915/intel_display.c
+++ b/drivers/gpu/drm/i915/intel_display.c
@@ -8622,8 +8622,10 @@  static void ironlake_set_pipeconf(struct drm_crtc 
*crtc)
                 BUG();
         }

-       if (intel_crtc->config->dither)
-               val |= (PIPECONF_DITHER_EN | PIPECONF_DITHER_TYPE_SP);
+       if (intel_crtc->config->dither) {
+               DRM_INFO("Ironlake wants dithering, but skipping dither 
enable!\n");
+               /* val |= (PIPECONF_DITHER_EN | PIPECONF_DITHER_TYPE_SP); */
+       }