Hi Tomi, On Tue, Dec 3, 2024 at 8:33 AM Tomi Valkeinen <tomi.valkeinen+renesas@xxxxxxxxxxxxxxxx> wrote: > On 02/12/2024 17:49, Geert Uytterhoeven wrote: > > On Fri, Oct 18, 2024 at 11:32 AM Geert Uytterhoeven > > <geert+renesas@xxxxxxxxx> wrote: > >> As I had to test Tomi's WIP patches to add mini-DP output support to > >> Gray Hawk Single, I moved my (old and new) DisplayPort gear to my board > >> farm, and thought this was a good opportunity to test mini-DP output on > >> White Hawk as a baseline (CN5), and add support for the second mini-DP > >> output on the White Hawk BreakOut board (CN15). > >> > >> For testing, I used the following hardware: > >> (A) BenQ BL2420PT desktop display (2560x1440), > >> (B) Joy-It Joy-View 15 portable display (1920x1080), > >> (C) Lindy DisplayPort to 2 Port HDMI MST Hub, > >> (D) Passive mini-DP to HDMI cable, > >> (E) LogiLink Mini DisplayPort to VGA Converter. > >> > >> (A)-(C) are known to work with my Intel desktop. > >> (D)-(E) are known to work with an old Dell XPS13. > >> > >> Software-wise, I used the frame buffer text console, "modetest -M > >> rcar-du -s 86:1920x1080@XR24" or "modetest -M rcar-du -s > >> 86:2560x1440@XR24", and fbtest. > >> > >> White Hawk CN5 > >> -------------- > >> > >> 1. Mini-DP to (A) DP: > >> - 2560x1440 works but flickers (flickering shifts image > >> horizontally; perhaps a cable issue, as 2 below does work?) > >> - 1920x1080 is stable > > > > While I don't have a second Mini-DP-to-DP-M cable, I tried a few > > other combos (now on Gray Hawk Single): > > 7. (D) + HDMI-F-F adapter + passive HDMI-F-to-DP-cable to (A) DP, > > D is passive DP->HDMI, it won't work. Are you saying it works, and the > result matches the test case 1.? It doesn't. I had hoped combining the two passive adapters would provide a valid galvanical DP conduit... > > > 8. Mini-DP-to-DP-F cable (=X) + plain DP cable (=Y) to (A) DP, > > unfortunately with the same results. Note that (X) is the same cable > > "same results" means same as in 1.? Oops, IIRC both 7 and 8 didn't work at all (monitor not detected). > > as used in scenario 2 below, and (Y) works fine with my Intel desktop. > > > > However, the maximum cable length for eDP seems to be 30 cm, so that > > Where did you read that? I don't think there's such a thing as "eDP https://www.lv-tron.com/edp-made-simple-quick-start-guide-with-experts-tips/ > cable". In laptops etc. eDP is connected to the panel via custom made > cables, and the cable design affects how long it can be. eDP and DP are i.e. an eDP cable ;-) > identical wrt. signaling, so using a DP cable with eDP or DP should > behave the same. > > That said, I don't think the eDP->DP connector designs we see in these > development boards are really made to match what one would expect from a > consumer device with a DP output. Indeed. And using a (too) long cable probably breaks this. > > may explain why 2 below is the only wiring that works at 2560x1440 > > (despite cable (X) being 1m, i.e. still too long)? > > > >> 2. Mini-DP to (C) to (A) HDMI: > >> - 2560x1440 OK > >> - 1920x1080 OK > > My guess is that this works, because there's an active component there > which decodes the DP input and re-encodes it to HDMI output, probably > with different timings (read, more standard). So the (C) is more > tolerant on not-so-standard DP input than (A) is. Yes, it has an active component, and a shorter cable. > The eDP chip is limited in its capabilities, e.g. back porch registers > are 8-bit, so they max out at 255. While those are checked in the > driver, I wouldn't be surprised if some other limitations are not (the > driver has clearly been written for eDP panels). > > You could try different custom timings with kmstest, to find if there's > something obvious that makes the case 1. work. For example, if the issue > is indeed the cable, probably lowering the pixel clock would fix it. So > using the same timings but dropping the pclk in half might get a stable > picture (then again, lowering pclk might fix many other kinds of issues > too...). The modes reported by modetest differ slightly between (1) and (2). (1) contains one additional 1920x1080 mode, but all other modes are the same. > Can you send your monitor's edid blob? I don't have a board up here, but > it should be available from somewhere in sysfs. On my desktop it's: > > /sys/devices/pci0000:00/0000:00:02.0/drm/card1/card1-DP-2/edid And in the modetest output. I'll send these by PM. Gr{oetje,eeting}s, Geert -- Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@xxxxxxxxxxxxxx In personal conversations with technical people, I call myself a hacker. But when I'm talking to journalists I just say "programmer" or something like that. -- Linus Torvalds
