From mboxrd@z Thu Jan  1 00:00:00 1970
From: Eugeni Dodonov <eugeni.dodonov@linux.intel.com>
Subject: Re: drm/i915: Disable DDI Pipe Control on HSW while
 disabling pipe
Date: Fri, 08 Jun 2012 10:50:00 -0300
Message-ID: <4FD20308.40700@linux.intel.com>
References: <1339136063-29548-1-git-send-email-shobhit.kumar@intel.com>
	<20120608124928.GB5761@phenom.ffwll.local>
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To: Daniel Vetter <daniel@ffwll.ch>
Cc: intel-gfx@lists.freedesktop.org
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On 06/08/2012 09:49 AM, Daniel Vetter wrote:
> On Fri, Jun 08, 2012 at 11:44:23AM +0530, Shobhit Kumar wrote:
>> In Haswell while disabling a pipe, we need to disable the DDI control as
>> well along with the PIPECONF. Otherwise we will hit assertions during crtc
>> disable
>
> Hm, can you add such an example assert with backtrace please? All these
> asserts encode our current understanding of the hw depency chain, so I'd
> like to check whether we're really doing the right thing and don't just
> stfu some dmesg noise.
>
> Thanks, Daniel

This is part of the pipe disabling process starting with Haswell. DDI 
pipe function control should be disabled when pipe is being disabled, 
otherwise it stays in enabled state and on next enabling we hit the 
assert within assert_fdi_tx:

...
         if (IS_HASWELL(dev_priv->dev)) {
                 /* On Haswell, DDI is used instead of FDI_TX_CTL */
                 reg = DDI_FUNC_CTL(pipe);
                 val = I915_READ(reg);
                 cur_state = !!(val & PIPE_DDI_FUNC_ENABLE);
...

I missed this in the initial enabling and Shobhit has catched this - thanks!

So you can also add:
Reviewed-by: Eugeni Dodonov <eugeni.dodonov@intel.com>

For this patch.

Eugeni