Imre Deak <imre.d...@intel.com> writes:
> On to, 2016-02-18 at 17:21 +0200, Mika Kuoppala wrote:
>> It has been observed that sometimes disabling the dc6 fails
>> and dc6 state pops back up, brief moment after disabling. This
>> has to be dmc save/restore timing issue or other bug in the
>> way dc states are handled.
>>
>> Try to work around this issue as we don't have firmware fix
>> yet available. Verify that the value we wrote for the dmc sticks,
>> and also enforce it by rewriting it, if it didn't.
>>
>> Testcase: kms_flip/basic-flip-vs-dpms
>> References: https://bugs.freedesktop.org/show_bug.cgi?id=93768
>> Cc: Patrik Jakobsson <patrik.jakobs...@linux.intel.com>
>> Cc: Rodrigo Vivi <rodrigo.v...@intel.com>
>> Cc: Imre Deak <imre.d...@intel.com>
>> Signed-off-by: Mika Kuoppala <mika.kuopp...@intel.com>
>> ---
>> drivers/gpu/drm/i915/intel_runtime_pm.c | 40
>> +++++++++++++++++++++++++++++++--
>> 1 file changed, 38 insertions(+), 2 deletions(-)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_runtime_pm.c
>> b/drivers/gpu/drm/i915/intel_runtime_pm.c
>> index 8b9290fdb3b2..cb91540cfbad 100644
>> --- a/drivers/gpu/drm/i915/intel_runtime_pm.c
>> +++ b/drivers/gpu/drm/i915/intel_runtime_pm.c
>> @@ -470,6 +470,42 @@ static void
>> gen9_set_dc_state_debugmask_memory_up(
>> }
>> }
>>
>> +static void gen9_write_dc_state(struct drm_i915_private *dev_priv,
>> + u32 state)
>> +{
>> + int rewrites = 0;
>> + int rereads = 0;
>> + u32 v;
>> +
>> + I915_WRITE(DC_STATE_EN, state);
>> +
>> + /* It has been observed that disabling the dc6 state
>> sometimes
>> + * doesn't stick and dmc keeps returning old value. Make
>> sure
>> + * the write really sticks enough times and also force
>> rewrite until
>> + * we are confident that state is exactly what we want.
>> + */
>> + do {
>> + v = I915_READ(DC_STATE_EN);
>> +
>> + if (v != state) {
>> + I915_WRITE(DC_STATE_EN, state);
>> + rewrites++;
>
> Could be rereads = 0; for extra paranoia. Either way:
Oh yes, extra paranoia in here is warranted. I will
add that.
> Reviewed-by: Imre Deak <imre.d...@intel.com>
Thanks,
-Mika
>
>> + } else if (rereads++ > 5) {
>> + break;
>> + }
>> +
>> + } while (rewrites < 100);
>> +
>> + if (v != state)
>> + DRM_ERROR("Writing dc state to 0x%x failed, now
>> 0x%x\n",
>> + state, v);
>> +
>> + /* Most of the times we need one retry, avoid spam */
>> + if (rewrites > 1)
>> + DRM_DEBUG_KMS("Rewrote dc state to 0x%x %d times\n",
>> + state, rewrites);
>> +}
>> +
>> static void gen9_set_dc_state(struct drm_i915_private *dev_priv,
>> uint32_t state)
>> {
>> uint32_t val;
>> @@ -502,8 +538,8 @@ static void gen9_set_dc_state(struct
>> drm_i915_private *dev_priv, uint32_t state)
>>
>> val &= ~mask;
>> val |= state;
>> - I915_WRITE(DC_STATE_EN, val);
>> - POSTING_READ(DC_STATE_EN);
>> +
>> + gen9_write_dc_state(dev_priv, val);
>>
>> dev_priv->csr.dc_state = val & mask;
>> }
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