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Date: Mon, 17 Apr 2023 09:53:28 +0200
From: qwx@sciops.net
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Subject: Re: [9front] displayport thinkpad x230 external monitor black screen
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On Sun Apr  9 08:58:34 +0200 2023, unobe@cpan.org wrote:
> I figured out the problem--the DisplayPort link training needed to be
> implemented more fully.  I didn't know really much at all about
> DisplayPort; that has changed.  I've attached a patch that implements
> pattern 1 & 2 training for HBR, along with fixing a couple other minor
> things I came across.[1]
> 
> I'd be curious if the patch works for you, igor and qwx.  I don't see
> why it wouldn't, but who knows.  Reader be warned: I'm not a C
> programmer, so I'm sure there's much that can be improved upon.

Alright, sorry for taking so long.  I'm going to test the patch on a
w500 and a w520 (resp.  gm965 and sandybridge, iirc) as soon as I'm
able.  I don't actually have any remarks on what you did itself, looks
good; I only have one comment on style: please be consistent with the
rest of the code, mostly add spacing around operators (for example the
shifts), and remove useless parenthesis (less important).  The only
other thing:

> +	while(--i){
> +		if(memcmp(tmp+i, magic, 8) == 0){
> +			trace("magic begins at index %d, shifting\n", i);
> +			memcpy(buf, tmp+i, 256-i);
> +			memcpy(buf+(256-i), tmp, i);
> +			i = 1;
> +		}
> +	}

Why not just a `break;' there?  Anyway, not important.


> To test my patch, I defined this test function to ensure I could get
> my working display back.  I didn't need to add anything to /lib/vgadb.
> 
> fn lg {
> 	@ {
> 		rfork n; aux/realemu; cd /sys/src/cmd/aux/vga; mk; /sys/src/cmd/aux/vga/6.out -v -V -m igfx -l 2560x1080; sleep 5; aux/vga -m igfx -l 1366x768
> 	}
> }

You don't need to run aux/realemu unless you will use vesa, which you
don't.  Also, in practice, do you still have to run aux/vga twice, or
is that just for testing?  Do you need this function at all now, that
is, does it not work by just having `monitor=auto' in plan9.ini?


@k0ga:

On Tue Apr 11 23:30:37 +0200 2023, k0ga@shike2.com wrote:
> I have one DP monitor here (qwx do you remember that we used it for our tests
> in the last hackathon ;) ?. I can try it but not in this week.

Yes, please do :) In fact, I bid anyone who has igfx to please check
for a regression :) Unfortunately, I don't have access for a few weeks
to other machines.  For reference, anything up to and including
broadwell (x250 generation) that has its pci device id in /lib/vgadb
and in /sys/src/cmd/aux/vga/igfx.c should still work with the
integrated screen, and now possibly with an external screen through DP
(not hdmi).

Thanks again!

Cheers,
qwx