Re: [PATCH 5/9] drm/i915: Clear out DPLL state from pipe config in DSI get config

[Sivakumar Thulasimani <sivakumar.thulasimani@intel.com>]

On 7/1/2015 6:12 PM, Daniel Vetter wrote:
> On Tue, Jun 30, 2015 at 02:50:33PM +0300, Ville Syrjälä wrote:
>> On Tue, Jun 30, 2015 at 12:13:37PM +0200, Daniel Vetter wrote:
>>> On Mon, Jun 29, 2015 at 08:08:27PM +0300, Ville Syrjälä wrote:
>>>> On Mon, Jun 29, 2015 at 07:56:05PM +0300, Ville Syrjälä wrote:
>>>>> On Mon, Jun 29, 2015 at 06:42:11PM +0200, Daniel Vetter wrote:
>>>>>> On Mon, Jun 29, 2015 at 03:25:52PM +0300, ville.syrjala@linux.intel.com wrote:
>>>>>>> From: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>>>>>>
>>>>>>> VLV/CHV don't use the DPLL with DSI, so just clear out the DPLL state
>>>>>>> from the pipe_config in intel_dsi_get_config(). This avoids spurious
>>>>>>> state checker warnings. We already did it this way for DPLL_MD, but do
>>>>>>> it for DPLL too.
>>>>>>>
>>>>>>> Toss in a WARN to intel_dsi_pre_enable() to make sure the ref clocks
>>>>>>> are enabled however. Supposedly they have some meaning to DSI too.
>>>>>>> We now keep the ref clocks always enabled while the disp2d well is
>>>>>>> enabled.
>>>>>>>
>>>>>>> Signed-off-by: Ville Syrjälä <ville.syrjala@linux.intel.com>
>>>>>>> ---
>>>>>>>   drivers/gpu/drm/i915/intel_dsi.c | 15 +++++----------
>>>>>>>   1 file changed, 5 insertions(+), 10 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/gpu/drm/i915/intel_dsi.c b/drivers/gpu/drm/i915/intel_dsi.c
>>>>>>> index 36e2148..92bb252 100644
>>>>>>> --- a/drivers/gpu/drm/i915/intel_dsi.c
>>>>>>> +++ b/drivers/gpu/drm/i915/intel_dsi.c
>>>>>>> @@ -421,18 +421,12 @@ static void intel_dsi_pre_enable(struct intel_encoder *encoder)
>>>>>>>   
>>>>>>>   	/* Disable DPOunit clock gating, can stall pipe
>>>>>>>   	 * and we need DPLL REFA always enabled */
>>>>>>> -	tmp = I915_READ(DPLL(pipe));
>>>>>>> -	tmp |= DPLL_REF_CLK_ENABLE_VLV;
>>>>>>> -	I915_WRITE(DPLL(pipe), tmp);
>>>>>>> -
>>>>>>> -	/* update the hw state for DPLL */
>>>>>>> -	intel_crtc->config->dpll_hw_state.dpll = DPLL_INTEGRATED_REF_CLK_VLV |
>>>>>>> -		DPLL_REF_CLK_ENABLE_VLV | DPLL_VGA_MODE_DIS;
>>>>>>> -
>>>>>>>   	tmp = I915_READ(DSPCLK_GATE_D);
>>>>>>>   	tmp |= DPOUNIT_CLOCK_GATE_DISABLE;
>>>>>>>   	I915_WRITE(DSPCLK_GATE_D, tmp);
>>>>>>>   
>>>>>>> +	WARN_ON((I915_READ(DPLL(pipe)) & DPLL_REF_CLK_ENABLE_VLV) == 0);
>>>>>>> +
>>>>>>>   	/* put device in ready state */
>>>>>>>   	intel_dsi_device_ready(encoder);
>>>>>>>   
>>>>>>> @@ -635,9 +629,10 @@ static void intel_dsi_get_config(struct intel_encoder *encoder,
>>>>>>>   	DRM_DEBUG_KMS("\n");
>>>>>>>   
>>>>>>>   	/*
>>>>>>> -	 * DPLL_MD is not used in case of DSI, reading will get some default value
>>>>>>> -	 * set dpll_md = 0
>>>>>>> +	 * DPLL is not used in case of DSI, reading will getsome default value.
>>>>>>> +	 * Clear the state to keep the state checker happy.
>>>>>>>   	 */
>>>>>>> +	pipe_config->dpll_hw_state.dpll = 0;
>>>>>>>   	pipe_config->dpll_hw_state.dpll_md = 0;
>>>>>> State configs are supposed to be kzallocated. Needing this indicates a
>>>>>> pretty serious bug - I'd vote to instead also ditch the dpll_md line and
>>>>>> fix the offender.
>>>>> There is no offender really. We read out the DPLL state before we know
>>>>> which ports are active and hence can't tell at that point if the
>>>>> information is really relevant.
>>> So the bios leaves the DPLL enabled even when using a DSI port? Or do we
>>> miss to check some routing bits in get_clock?
>> Not necessarily enabled, but there are other bits in there that could be
>> left in any state basically. The DSI port simply doesn't care.
> If the enable bit is what's gating things here then we should just forgo
> reading out any dpll register state if that's not set. Looking at the
> vlv/chv state readout code that seems to be the trouble - there's nothing
> guarding the register reads into the pipe_config at all. Didn't matter
> pre-vlv without dsi since enable pipe should imply enabled dpll, but
> obviously won't work correctly with dsi. Can you please spin such a patch
> and remove the hacks here from dsi_get_config?
> -Daniel
Not sure i understand the point of contention here, just noticed this 
after i gave my RB :)
so my justification on why this is proper is that DSI is not supposed to 
touch DPLL register
any place we access dpll_hw_state.dpll is under !is_dsi check so that 
ensures that we dont
program DPLL register for dsi panel. it was wrong to have originally 
modfied DPLL register
inside intel_dsi_pre_enable so removal is fine. setting it to zero in 
intel_dsi_get_config
is of no impact since any place we write back the contents of 
dpll_hw_state is past the
!is_dsi check is never consumed by anyone as long as the CRTC uses DSI.

-- 
regards,
Sivakumar

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