[Intel-gfx] PROBLEM: i915 Haswell KMS wrong maximum resolution

[Bruno Prémont]

Hi Kenneth,

On Sun, 30 March 2014 Kenneth de Mello wrote:
> What about dual-link DVI?   I though the additional link addressed the
> pixel clock limitation.   Has it only been using a single link this entire
> time, and it's only worked by ignoring the maximum dotclock, so in other
> words, the fact it works at all is the bug?
> 
> Also, the commit that rejects mode exceeding 165MHz states:
> 
>     "Single-link DVI max dotclock is 165MHz. Filter out modes with higher
>      dotclock when the monitor doesn't support HDMI."
> 
> Does this mean HDMI in general?   This monitor does support HDMI, but the
> maximum resolution when using the physical HDMI ports is 1920x1080.
> 
> What is the solution here, to switch to displayport if I want to use kernel
> 3.13.7 and beyond?   (This is fine, I just need to know so I can buy the
> cable).

I don't know the details, just spotting a possible match. Revert that
patch and try, just to make sure it's the cause.
Also try latest 3.14-rc (or release if it happens early enough).

Looking at the patch I don't see anything that would distinguish
single-link and dual-link DVI, but that might be located in the code
around (if so, possibly only in 3.14-rcX).


Note that the debug info you provided has pretty limited extract of
kernel logs.
Try to get more complete dmesg (at least starting from initialization of
i915) as well as Xorg.log.
Possibly you will have to get the same info with non-zero drm.debug
kernel cmdline option (or debug drm module option). But what value is
best is beyond my expertise.

I don't know if it's possible for the GPU to determine if DVI cable is
single or dual-link, but with single-link cable and such a monitor
you get some image to the monitor but with weird "scaling" effects!

Bruno


> Kenneth
> 
> On Sun, Mar 30, 2014 at 2:36 PM, Bruno Prémont wrote:
> > Hi Kenneth,
> >
> > On Fri, 28 March 2014 Kenneth de Mello wrote:
> > > On my system, the maximum resolution of my monitor, 2560x1440, is no
> > longer
> > > automatically detected properly with kernel 3.13.7.   This worked with
> > > 3.13.6, and 5 with this hardware and identical kernel configs.    Now the
> > > autodetected resolution is 1920x1080.
> > >
> > > The monitor is plugged into the DVI port on my motherboard.
> > >
> > > My system:
> > >
> > > - i7-4770 (non-K) CPU
> > > - asrock z87 extreme6 motherboard
> > > - Dell U2711 monitor
> > >
> > > The integrated graphics adapter is configured as the primary in the BIOS,
> > > and the discreet card is passed through to a Xen guest.   Kernel 3.13.7
> > > mis-detects the resolution regardless if it is being booted with Xen or
> > > without it (and previous versions worked as expected).  More detailed
> > > system information is attached.
> > >
> > > I don't notice any unusual messages, other than the wrong resolution.
> > >
> > > Steps to reproduce:  Boot with kernel 3.13.7 (with or without Xen)
> > >
> > > I'd be happy to provide more detail if required.
> >
> > This smells like the following change in 3.13.6 to 3.13.7 might
> > be the cause:
> >
> > commit e3ea8fa6beaf55fee64bf816f3b8a80ad733b2c2
> > Author: Ville Syrjälä <ville.syrjala at linux.intel.com>
> > Date:   Mon Mar 3 11:33:36 2014 +0200
> >
> >     drm/i915: Reject >165MHz modes w/ DVI monitors
> >
> >     commit 6375b768a9850b6154478993e5fb566fa4614a9c upstream.
> >
> >     Single-link DVI max dotclock is 165MHz. Filter out modes with higher
> >     dotclock when the monitor doesn't support HDMI.
> >
> >     Modes higher than 165 MHz were allowed in
> >
> >     commit 7d148ef51a657fd04036c3ed7803da600dd0d451
> >     Author: Daniel Vetter <daniel.vetter at ffwll.ch>
> >     Date:   Mon Jul 22 18:02:39 2013 +0200
> >
> >         drm/i915: fix hdmi portclock limits
> >
> >     Also don't attempt to use 12bpc mode with DVI monitors.
> >
> >     Cc: Adam Nielsen <a.nielsen at shikadi.net>
> >     Bugzilla: https://bugs.freedesktop.org/show_bug.cgi?id=75345
> >     Bugzilla: https://bugzilla.kernel.org/show_bug.cgi?id=70331
> >     Tested-by: Ralf Jung <post+kernel at ralfj.de>
> >     Signed-off-by: Ville Syrjälä <ville.syrjala at linux.intel.com>
> >     Signed-off-by: Jani Nikula <jani.nikula at intel.com>
> >     Signed-off-by: Greg Kroah-Hartman <gregkh at linuxfoundation.org>
> >
> >
> > Bruno
> >