linux-kernel - Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver

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Message-ID: <ab010164-e8ea-89e9-a7e9-d7213841fa90@nvidia.com>
Date:   Fri, 10 Apr 2020 11:59:09 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>, <thierry.reding@...il.com>,
        <jonathanh@...dia.com>, <frankc@...dia.com>, <hverkuil@...all.nl>,
        <sakari.ailus@....fi>, <helen.koike@...labora.com>
CC:     <sboyd@...nel.org>, <linux-media@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-clk@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [RFC PATCH v6 6/9] media: tegra: Add Tegra210 Video input driver


On 4/10/20 11:47 AM, Dmitry Osipenko wrote:
> External email: Use caution opening links or attachments
>
>
> 09.04.2020 21:28, Sowjanya Komatineni пишет:
>> On 4/9/20 7:50 AM, Dmitry Osipenko wrote:
>>> External email: Use caution opening links or attachments
>>>
>>>
>>> 09.04.2020 06:38, Sowjanya Komatineni пишет:
>>> ...
>>>> Tested with 3 buffers and by checking outstanding buffers in process by
>>>> VI hw and holding to start capture till one outstanding buffer in
>>>> process by HW.
>>>> Also tested with 2 buffers without checking for outstanding buffers.
>>>>
>>>> In both cases, I see same %CPU for the kthreads and is < 1%
>>>>
>>> I don't see where buffers queue max limit is set to 3 in the code, but
>>> should be okay if CPU isn't getting hogged. Looking forward to v7.
>> Sorry, correction I meant to say pre-queued buffers before streaming not
>> num_buffers.
>> vb2 queue min_buffers_needed was set to 3 as part of one of the issue
>> debug in earlier version which actually was irrelevant to that issue and
>> should have been removed. Will remove min_buffers_needed in v7.
>>
>> I added checking for outstanding requests by hardware just to be safer
>> although we may not hit this case of issuing more than 1 outstanding
>> frame capture to VI hardware as capture_frame() waits till it sees frame
>> start event through HW syncpt increment before proceeding for memory
>> write and issuing next frame capture.
>>
>> So issuing frame captures are synchronized with frame start and frame end.
>>
>> Will remove min_buffers_needed and also explicit check for outstanding
>> buffers in v7.
> It's still not clear to me how the "pre-queued buffers" will be limited.
> I'll take another look at the v7.

OK, but I don't understand what you mean by limit on pre-queued buffers.

I was saying vb2 queue has min_buffers_needed which was set to 3 where 
streaming will start only after 3 buffers got queued up.

Regarding outstanding condition check to make sure no more than 2 syncpt 
trigger requests are in FIFO I added it to be safe where mostly we may 
not hit and also I only see capture start thread holding for it during 
initial frame capture as it issues single shot for 1st 2 buffers capture 
and holds 3 buffers which is already queued till at least one of those 2 
issued capture is done to make sure of not triggering syncpt condition 
when fifo already has 2 pending.

In v7, will remove setting min_buffers_needed and also outstanding 
syncpt trigger check.