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From: Neil Mayhew <neil_mayhew-Rn4VEauK+AKRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>
To: amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org
Subject: Re: 21:9 monitor resolution incorrect since 4.14 kernel
Date: Wed, 30 Oct 2019 12:07:38 -0600	[thread overview]
Message-ID: <10434d28-490d-ebbd-ab66-d3adb3a2e1de@users.sourceforge.net> (raw)
In-Reply-To: <32e595a2-fdc1-7b13-2e33-c2b8752c60f2-Rn4VEauK+AKRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>


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I enabled kms debugging with drm.debug=4 on the kernel command line.
This enabled me to see that the relevant modes are being rejected with
error 11 which is DC_EXCEED_DONGLE_CAP. Sure enough, I see that there's
a dongle detected that's rated at 165MHz and my preferred modes are all
above that.

However, if I switch the monitors around everything is fine, because I
can use a lower resolution monitor with the dongle and get the 21:9
resolution on another output without a dongle.

The dongle is actually a passive DP to HDMI cable, and I need it because
one of my outputs is DP and I don't have any monitors with DP inputs. I
was told somewhere that I'd need to use the DP output to get the clock
speeds needed for 21:9, but apparently that's not true. Clearly the
cable can go above 165MHz since the 4.14 kernel can drive the display at
the preferred resolution using it, but thankfully I don't need to
concern myself with that now.

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      parent reply	other threads:[~2019-10-30 18:07 UTC|newest]

Thread overview: 3+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-10-29 22:01 21:9 monitor resolution incorrect since 4.14 kernel Neil Mayhew
2019-10-29 22:01 ` Neil Mayhew
     [not found] ` <32e595a2-fdc1-7b13-2e33-c2b8752c60f2-Rn4VEauK+AKRv+LV9MX5uipxlwaOVQ5f@public.gmane.org>
2019-10-30 18:07   ` Neil Mayhew [this message]

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