Re: [Intel-gfx] [Regression] "drm/i915: Implement display w/a #1143" breaks HDMI on ASUS GL552VW

["Ville Syrjälä" <ville.syrjala@linux.intel.com>]

On Mon, Aug 17, 2020 at 02:17:49PM +0800, Kai-Heng Feng wrote:
> 
> 
> > On Aug 17, 2020, at 00:22, Runyan, Arthur J <arthur.j.runyan@intel.com> wrote:
> > 
> > You'll need to read out the DDI_BUF_TRANS_* and DISPIO_CR_TX_BMU_CR0 registers at boot before i915 programs them and compare with what driver programs.  
> > Rodrigo can probably show you how. 
> 
> Right, I'll wait for a patch then :)

To grab the BIOS reg values we just have to make sure the driver
doesn't load. Eg. pass something like 
"modprobe.blacklist=i915,snd_hda_intel 3" to the kernel cmdline
(+ whatever other magic ubuntu might require). Confirm with
something like "lsmod | grep i915" to make sure the driver didn't
sneak in despite our best efforts.

Then we can dump the registers with intel_reg from igt-gpu-tools:
intel_reg read --count 20 0x64E00 0x64E60 0x64EC0 0x64F20 0x64F80
intel_reg read 0x64000 0x64100 0x64200 0x64300 0x64400 0x6C00C

The only somewhat suspicious thing I noticed is that we treat
DISPIO_CR_TX_BMU_CR0:tx_blnclegdisbl as a bitmask (bit 23 -> DDI A,
bit 24 -> DDI B, etc.) whereas the spec seems to be saying that we
should just zero out all the bits of tx_blnclegdisbl when any DDI
needs iboost. Art, is our interpretation of the bits correct or just
a fairy tale?

> 
> Kai-Heng
> 
> > 
> > -----Original Message-----
> > From: Kai-Heng Feng <kai.heng.feng@canonical.com> 
> > Sent: Thursday, August 13, 2020 10:14 PM
> > To: Runyan, Arthur J <arthur.j.runyan@intel.com>
> > Cc: Vivi, Rodrigo <rodrigo.vivi@intel.com>; Ville Syrjälä <ville.syrjala@linux.intel.com>; intel-gfx <intel-gfx@lists.freedesktop.org>
> > Subject: Re: [Regression] "drm/i915: Implement display w/a #1143" breaks HDMI on ASUS GL552VW
> > 
> > Hi,
> > 
> >> On Aug 14, 2020, at 01:56, Runyan, Arthur J <arthur.j.runyan@intel.com> wrote:
> >> 
> >> The workaround is freeing up stuck vswing values to let new vswing programming kick in.  Maybe the new vswing values are wrong.
> >> Try checking the vswing that driver programs against what BIOS/GOP programs.
> > 
> > Do you mean to print out value of I915_READ()?
> > val = I915_READ(CHICKEN_TRANS(transcoder));
> > 
> > Kai-Heng
> > 
> >> 
> >> -----Original Message-----
> >> From: Vivi, Rodrigo <rodrigo.vivi@intel.com>
> >> Sent: Thursday, August 13, 2020 9:50 AM
> >> To: Kai-Heng Feng <kai.heng.feng@canonical.com>; Runyan, Arthur J 
> >> <arthur.j.runyan@intel.com>
> >> Cc: Ville Syrjälä <ville.syrjala@linux.intel.com>; intel-gfx 
> >> <intel-gfx@lists.freedesktop.org>
> >> Subject: Re: [Regression] "drm/i915: Implement display w/a #1143" 
> >> breaks HDMI on ASUS GL552VW
> >> 
> >> Art, any comment here?
> >> 
> >> I just checked and the  W/a 1143 is implemented as described, but it is failing HDMI on this hybrid system.
> >> 
> >>> On Aug 12, 2020, at 9:07 PM, Kai-Heng Feng <kai.heng.feng@canonical.com> wrote:
> >>> 
> >>> Hi,
> >>> 
> >>> There's a regression reported that HDMI output stops working after os upgrade:
> >>> https://bugs.launchpad.net/bugs/1871721
> >>> 
> >>> Here's the bisect result:
> >>> 0519c102f5285476d7868a387bdb6c58385e4074 is the first bad commit 
> >>> commit 0519c102f5285476d7868a387bdb6c58385e4074
> >>> Author: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >>> Date:   Mon Jan 22 19:41:31 2018 +0200
> >>> 
> >>>  drm/i915: Implement display w/a #1143
> >>> 
> >>>  Apparently SKL/KBL/CFL need some manual help to get the
> >>>  programmed HDMI vswing to stick. Implement the relevant
> >>>  workaround (display w/a #1143).
> >>> 
> >>>  Note that the relevant chicken bits live in a transcoder register
> >>>  even though the bits affect a specific DDI port rather than a
> >>>  specific transcoder. Hence we must pick the correct transcoder
> >>>  register instance based on the port rather than based on the
> >>>  cpu_transcoder.
> >>> 
> >>>  Also note that for completeness I included support for DDI A/E
> >>>  in the code even though we never have HDMI on those ports.
> >>> 
> >>>  v2: CFL needs the w/a as well (Rodrigo and Art)
> >>> 
> >>>  Cc: Rodrigo Vivi <rodrigo.vivi@intel.com>
> >>>  Cc: Art Runyan <arthur.j.runyan@intel.com>
> >>>  Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
> >>>  Link: https://patchwork.freedesktop.org/patch/msgid/20180122174131.28046-1-ville.syrjala@linux.intel.com
> >>>  Reviewed-by: Rodrigo Vivi <rodrigo.vivi@intel.com>
> >>> 
> >>> 
> >>> dmesg from drm-tip with drm.debug=0xe can be found here:
> >>> https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1871721/comments
> >>> /
> >>> 64
> >>> 
> >>> Kai-Heng
> >> 
> >> 
> > 

-- 
Ville Syrjälä
Intel
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