Re: [PATCH] drm/i915: Always recompute watermarks when distrust_bios_wm is set

[Maarten Lankhorst <maarten.lankhorst@linux.intel.com>]

Op 31-05-17 om 12:42 schreef Mahesh Kumar:
> Hi,
>
>
> On Wednesday 31 May 2017 01:26 PM, Maarten Lankhorst wrote:
>> On some systems there can be a race condition in which no crtc state is
>> added to the first atomic commit. This results in all crtc's having a
>> null DDB allocation, causing a FIFO underrun on any update until the
>> first modeset.
>>
>> Reported-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> Inspired-by: Mahesh Kumar <mahesh1.kumar@intel.com>
>> Signed-off-by: Maarten Lankhorst <maarten.lankhorst@linux.intel.com>
>> Fixes: 98d39494d375 ("drm/i915/gen9: Compute DDB allocation at atomic
>> check time (v4)")
>> Cc: <stable@vger.kernel.org> # v4.8+
>> Cc: Mahesh Kumar <mahesh1.kumar@intel.com>
>> Cc: Matt Roper <matthew.d.roper@intel.com>
>> ---
>>   drivers/gpu/drm/i915/intel_pm.c | 18 ++++++++++++++++++
>>   1 file changed, 18 insertions(+)
>>
>> diff --git a/drivers/gpu/drm/i915/intel_pm.c b/drivers/gpu/drm/i915/intel_pm.c
>> index a488e068c3d6..8daa382b47f3 100644
>> --- a/drivers/gpu/drm/i915/intel_pm.c
>> +++ b/drivers/gpu/drm/i915/intel_pm.c
>> @@ -5037,10 +5037,27 @@ skl_compute_wm(struct drm_atomic_state *state)
>>       struct drm_crtc_state *cstate;
>>       struct intel_atomic_state *intel_state = to_intel_atomic_state(state);
>>       struct skl_wm_values *results = &intel_state->wm_results;
>> +    struct drm_device *dev = state->dev;
>>       struct skl_pipe_wm *pipe_wm;
>>       bool changed = false;
>>       int ret, i;
>>   +    if (to_i915(dev)->wm.distrust_bios_wm) {
>> +        changed = true;
>> +
>> +        /*
>> +         * The first commit after driver load must update the ddb
>> +         * allocations, so make sure we at least hold a lock to
>> +         * inspect the state required for watermark updates.
>> +         *
>> +         * Below we'll grab the required crtc state.
>> +         */
>> +        ret = drm_modeset_lock(&dev->mode_config.connection_mutex,
>> +                       state->acquire_ctx);
> Do we need to get lock here?
> We will anyway go ahead & get the connection_mutex lock during skl_compute_ddb based on distruct_bios_wm flag. 
Oh right, missed that one, yeah ignore it. :)

I'll send the original patch again, thanks for catching.

~Maarten