[PATCH v2 05/27] drm/msm/dpu: drop EAGAIN check from dpu_format_populate_layout

[Dmitry Baryshkov]

On 28/01/2023 01:59, Abhinav Kumar wrote:
> 
> 
> On 1/26/2023 10:05 PM, Dmitry Baryshkov wrote:
>> On Fri, 27 Jan 2023 at 02:52, Abhinav Kumar 
>> <quic_abhinavk at quicinc.com> wrote:
>>>
>>>
>>>
>>> On 12/29/2022 11:18 AM, Dmitry Baryshkov wrote:
>>>> The pipe's layout is not cached, corresponding data structure is zeroed
>>>> out each time in the dpu_plane_sspp_atomic_update(), right before the
>>>> call to _dpu_plane_set_scanout() -> dpu_format_populate_layout().
>>>>
>>>> Drop plane_addr comparison against previous layout and corresponding
>>>> EAGAIN handling.
>>>>
>>>> Signed-off-by: Dmitry Baryshkov <dmitry.baryshkov at linaro.org>
>>>
>>> The change itself LGTM, hence
>>>
>>> But, shouldnt we add this EAGAIN validation or in other words fix this
>>> rather than drop this?
>>
>> What for? Does it really save us anything? What's the price of
>> re-programming the SSPP_SRC0_ADDR registers?
>>
> There are 4 Src registers being programmed per sspp.
> 
> With number of layers going up this will be 4x.
> 
> So lets say there are 5 layers and only one of their address has 
> changed, we need to reprogram only 4 regs but now will reprogram 20.

I think this was the original intention for this change, however the 
implementation ended up being written in a way when this condition 
doesn't trigger at all.

> 
> Thats why i thought this is a good optimization.
> 
> But still, that is a separate change so I am fine if this goes in first 
> as its just removing dead code anyway.
> 
> Reviewed-by: Abhinav Kumar <quic_abhinavk at quicinc.com>
-- 
With best wishes
Dmitry