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

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Message-ID: <00708f34-cf45-e248-c6b0-c3d2286671ca@gmail.com>
Date:   Fri, 10 Apr 2020 21:47:50 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.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

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.