Re: [PATCH v3 6/9] drm/bridge: ti-sn65dsi86: Use 18-bit DP if we can

[Doug Anderson <dianders@chromium.org>]

Hi,

On Thu, Jul 9, 2020 at 11:15 PM Steev Klimaszewski <steev@kali.org> wrote:
>
> Hi,
>
> On 7/9/20 11:12 PM, Doug Anderson wrote:
> >> root@c630:~# bus=$(i2cdetect -l | grep sn65 | sed 's/i2c-\([0-9]*\).*$/\1/')
> >> root@c630:~# i2cdump ${bus} 0x50 i > edid
> >> WARNING! This program can confuse your I2C bus, cause data loss and worse!
> >> I will probe file /dev/i2c-16, address 0x50, mode i2c block
> >> Continue? [Y/n]
> >> root@c630:~# edid-decode edid
> >> edid-decode (hex):
> >>
> >> 00 ff ff ff ff ff ff 00 09 e5 d1 07 00 00 00 00
> >> 01 1c 01 04 a5 1d 11 78 0a 1d b0 a6 58 54 9e 26
> >> 0f 50 54 00 00 00 01 01 01 01 01 01 01 01 01 01
> >> 01 01 01 01 01 01 c0 39 80 18 71 38 28 40 30 20
> >> 36 00 26 a5 10 00 00 1a 00 00 00 00 00 00 00 00
> >> 00 00 00 00 00 00 00 00 00 1a 00 00 00 fe 00 42
> >> 4f 45 20 43 51 0a 20 20 20 20 20 20 00 00 00 fe
> >> 00 4e 56 31 33 33 46 48 4d 2d 4e 36 31 0a 00 9a
> >>
> >> 03 26 0a 77 ab 1c 05 71 6f 1d 8c f1 43 ce 6a bb
> >> fb d3 11 20 39 07 22 6e 65 68 77 70 d3 05 34 73
> >> 44 21 8b fd f5 6d 11 62 94 2a 7c fa 93 ba 6a 61
> >> 92 da 15 53 4c 39 eb f7 86 23 97 48 e9 39 09 d2
> >> 66 02 70 bb e2 77 0f 4a a3 a0 4c 72 6e 5d 47 70
> >> 43 c2 13 f3 b2 d9 b9 78 02 be 41 82 15 6a 28 dc
> >> 45 0f 9d eb 0f 2a cc e8 35 8d 34 7f 3e 84 5e a3
> >> 30 5e 1e 29 0a 48 0c d1 0a c4 08 31 03 a9 3b 29
> >>
> >> ----------------
> >>
> >> EDID version: 1.4
> >> Manufacturer: BOE Model 2001 Serial Number 0
> >> Made in week 1 of 2018
> >> Digital display
> >> 8 bits per primary color channel
> >> DisplayPort interface
> >> Maximum image size: 29 cm x 17 cm
> >> Gamma: 2.20
> >> Supported color formats: RGB 4:4:4, YCrCb 4:4:4
> >> First detailed timing includes the native pixel format and preferred
> >> refresh rate
> >> Color Characteristics
> >>     Red:   0.6484, 0.3447
> >>     Green: 0.3310, 0.6181
> >>     Blue:  0.1503, 0.0615
> >>     White: 0.3125, 0.3281
> >> Established Timings I & II: none
> >> Standard Timings: none
> >> Detailed mode: Clock 147.840 MHz, 294 mm x 165 mm
> >>                  1920 1968 2000 2200 ( 48  32 200)
> >>                  1080 1083 1089 1120 (  3   6  31)
> >>                  +hsync -vsync
> >>                  VertFreq: 60.000 Hz, HorFreq: 67.200 kHz
> >> Manufacturer-Specified Display Descriptor (0x00): 00 00 00 00 00 00 00
> >> 00 00 00 00 00 00 00 00 1a  ................
> >> Alphanumeric Data String: BOE CQ
> >> Alphanumeric Data String: NV133FHM-N61
> >> Checksum: 0x9a
> >>
> >> ----------------
> >>
> >> Unknown EDID Extension Block 0x03
> >>     03 26 0a 77 ab 1c 05 71 6f 1d 8c f1 43 ce 6a bb .&.w...qo...C.j.
> >>     fb d3 11 20 39 07 22 6e 65 68 77 70 d3 05 34 73  ... 9."nehwp..4s
> >>     44 21 8b fd f5 6d 11 62 94 2a 7c fa 93 ba 6a 61 D!...m.b.*|...ja
> >>     92 da 15 53 4c 39 eb f7 86 23 97 48 e9 39 09 d2 ...SL9...#.H.9..
> >>     66 02 70 bb e2 77 0f 4a a3 a0 4c 72 6e 5d 47 70 f.p..w.J..Lrn]Gp
> >>     43 c2 13 f3 b2 d9 b9 78 02 be 41 82 15 6a 28 dc C......x..A..j(.
> >>     45 0f 9d eb 0f 2a cc e8 35 8d 34 7f 3e 84 5e a3 E....*..5.4.>.^.
> >>     30 5e 1e 29 0a 48 0c d1 0a c4 08 31 03 a9 3b 29 0^.).H.....1..;)
> >> Checksum: 0x29 (should be 0x82)
> >>
> >>
> >> - My edid does in fact say it's 8bit
> > Crazy!  Mine:
> >
> > Extracted contents:
> > header:          00 ff ff ff ff ff ff 00
> > serial number:   09 e5 2d 08 00 00 00 00 23 1c
> > version:         01 04
> > basic params:    95 1d 11 78 02
> > chroma info:     d5 00 a6 58 54 9f 27 0f 4f 57
> > established:     00 00 00
> > standard:        01 01 01 01 01 01 01 01 01 01 01 01 01 01 01 01
> > descriptor 1:    c0 39 80 18 71 38 28 40 30 20 36 00 26 a5 10 00 00 1a
> > descriptor 2:    00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00 00
> > descriptor 3:    00 00 00 fe 00 42 4f 45 20 43 51 0a 20 20 20 20 20 20
> > descriptor 4:    00 00 00 fe 00 4e 56 31 33 33 46 48 4d 2d 4e 36 32 0a
> > extensions:      00
> > checksum:        40
> >
> > Manufacturer: BOE Model 82d Serial Number 0
> > Made week 35 of 2018
> > EDID version: 1.4
> > Digital display
> > 6 bits per primary color channel
> > DisplayPort interface
> > Maximum image size: 29 cm x 17 cm
> > Gamma: 2.20
> > Supported color formats: RGB 4:4:4
> > First detailed timing is preferred timing
> > Established timings supported:
> > Standard timings supported:
> > Detailed mode: Clock 147.840 MHz, 294 mm x 165 mm
> >                 1920 1968 2000 2200 hborder 0
> >                 1080 1083 1089 1120 vborder 0
> >                 +hsync -vsync
> > Manufacturer-specified data, tag 0
> > ASCII string: BOE
> > ASCII string: NV133FHM-N62
> > Checksum: 0x40 (valid)
> >
> > Unknown extension block
> >
> > EDID block does NOT conform to EDID 1.3!
> >          Missing name descriptor
> >          Missing monitor ranges
> >          Detailed block string not properly terminated
> > EDID block does not conform at all!
> >          Has 128 nonconformant extension block(s)
>
> I did attempt to modify the patch, and I don't think I did it correctly
>
> Around line 232, I changed
>
> IS_SC7180_TARGET(c->hw.hwversion))
>
> to
>
> IS_SC7180_TARGET(c->hw.hwversion) ||
>
> IS_SDM845_TARGET(c->hw.hwversion))
>
>
> But it would seem that only gets us 1/2 way there...
>
> https://dev.gentoo.org/~steev/files/image2.jpg
>
>
> But should I continue on this path,

It's probably worth getting dithering working on your sdm845 anyway in
case anyone actually does put a 6bpp panel on this SoC.


> or should we be finding others who
> have an N61 and see what their EDID reports?

I have an email out to BOE, but it might take a little while to get a
response.  I'll see what they say.  If they say that the panel
actually supports 8bpp then it's a no-brainer and we should just
switch to 8bpp and be done.

...but if they say it's a 6bpp panel that has its own dither logic
then it gets more complicated.  Initially one would think there should
be very little downside in defining the panel as an 8bpp panel and
calling it done.  ...except that it conflicts with some other work
that I have in progress.  :-P  Specifically if you treat the panel as
6bpp and then reduce the blanking a tiny bit you can actually save 75
mW of total system power on my board (probably similar on your board
since you have the same bridge chip).  You can see a patch to do that
here:

https://crrev.com/c/2276384

...so I'm hoping to get some clarity from BOE both on the true bits
per pixel and whether my proposed timings are valid before moving
forward.  Is that OK?


-Doug