[Intel-gfx] [PATCH v3 2/9] drm/i915/skl+: use linetime latency instead of ddb size

[Mahesh Kumar]

Hi,


On Monday 19 September 2016 11:54 PM, Zanoni, Paulo R wrote:
> Em Seg, 2016-09-19 às 15:19 -0300, Paulo Zanoni escreveu:
>> Em Sex, 2016-09-09 às 13:30 +0530, Kumar, Mahesh escreveu:
>>> From: Mahesh Kumar <mahesh1.kumar at intel.com>
>>>
>>> This patch make changes to use linetime latency instead of
>>> allocated
>>> DDB size during plane watermark calculation in switch case, This is
>>> required to implement new DDB allocation algorithm.
>>>
>>> In New Algorithm DDB is allocated based on WM values, because of
>>> which
>>> number of DDB blocks will not be available during WM calculation,
>>> So this "linetime latency" is suggested by SV/HW team to use during
>>> switch-case for WM blocks selection.
>> Why is this not part of BSpec? If there's some problem with the
>> current
>> algorithm and we need a new one, why is it not part of our spec?
>>
This is now included in BSpec.... :)
>>>
>>> Changes since v1:
>>>   - Rebase on top of Paulo's patch series
>>>
>>> Signed-off-by: Mahesh Kumar <mahesh1.kumar at intel.com>
>>> ---
>>>   drivers/gpu/drm/i915/intel_pm.c | 7 ++++++-
>>>   1 file changed, 6 insertions(+), 1 deletion(-)
>>>
>>> diff --git a/drivers/gpu/drm/i915/intel_pm.c
>>> b/drivers/gpu/drm/i915/intel_pm.c
>>> index 3fdec4d..cfd9b7d1 100644
>>> --- a/drivers/gpu/drm/i915/intel_pm.c
>>> +++ b/drivers/gpu/drm/i915/intel_pm.c
>>> @@ -3622,10 +3622,15 @@ static int skl_compute_plane_wm(const
>>> struct
>>> drm_i915_private *dev_priv,
>>>   	    fb->modifier[0] == I915_FORMAT_MOD_Yf_TILED) {
>>>   		selected_result = max(method2, y_tile_minimum);
>>>   	} else {
>>> +		uint32_t linetime_us = 0;
>>> +
>>> +		linetime_us = DIV_ROUND_UP(width * 1000,
>>> +				skl_pipe_pixel_rate(cstate));
> Also, shouldn't this be width * 8 * 1000?
we don't need to multiply by 8 here, as this is the time taken for 
single line to be fetched.

thanks,
-Mahesh
>
>>> +
>>>   		if ((cpp * cstate->base.adjusted_mode.crtc_htotal
>>> /
>>> 512 < 1) &&
>>>   		    (plane_bytes_per_line / 512 < 1))
>>>   			selected_result = method2;
>>> -		else if ((ddb_allocation / plane_blocks_per_line)
>>>> =
>>> 1)
>>> +		if (latency >= linetime_us)
>>>   			selected_result = min(method1, method2);
>>>   		else
>>>   			selected_result = method1;
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