From mboxrd@z Thu Jan 1 00:00:00 1970 From: Neil Mayhew Subject: Re: 21:9 monitor resolution incorrect since 4.14 kernel Date: Wed, 30 Oct 2019 12:07:38 -0600 Message-ID: <10434d28-490d-ebbd-ab66-d3adb3a2e1de@users.sourceforge.net> References: <32e595a2-fdc1-7b13-2e33-c2b8752c60f2@users.sourceforge.net> Mime-Version: 1.0 Content-Type: multipart/mixed; boundary="===============1010886320==" Return-path: In-Reply-To: <32e595a2-fdc1-7b13-2e33-c2b8752c60f2-Rn4VEauK+AKRv+LV9MX5uipxlwaOVQ5f@public.gmane.org> Content-Language: en-CA List-Id: Discussion list for AMD gfx List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: amd-gfx-bounces-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org Sender: "amd-gfx" To: amd-gfx-PD4FTy7X32lNgt0PjOBp9y5qC8QIuHrW@public.gmane.org This is a multi-part message in MIME format. --===============1010886320== Content-Type: multipart/alternative; boundary="------------429F2F58935EC85F010C4293" Content-Language: en-CA This is a multi-part message in MIME format. --------------429F2F58935EC85F010C4293 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: quoted-printable I enabled kms debugging with drm.debug=3D4 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. --------------429F2F58935EC85F010C4293 Content-Type: text/html; charset=utf-8 Content-Transfer-Encoding: 8bit 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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