linux-kernel - Re: [RFC PATCH v3 16/18] gpu: host1x: mipi: Split tegra_mipi_calibrate and tegra_mipi

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Date:   Thu, 16 Jul 2020 16:09:20 -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>, <robh+dt@...nel.org>,
        <helen.koike@...labora.com>
CC:     <sboyd@...nel.org>, <gregkh@...uxfoundation.org>,
        <linux-media@...r.kernel.org>, <devicetree@...r.kernel.org>,
        <linux-tegra@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <linux-i2c@...r.kernel.org>
Subject: Re: [RFC PATCH v3 16/18] gpu: host1x: mipi: Split
 tegra_mipi_calibrate and tegra_mipi_wait


On 7/16/20 4:06 PM, Sowjanya Komatineni wrote:
>
> On 7/16/20 4:01 PM, Dmitry Osipenko wrote:
>> 17.07.2020 01:49, Sowjanya Komatineni пишет:
>>>> What keeps MIPI clock enabled after completion of the
>>>> tegra_mipi_calibrate() invocation?
>>> MIPI clock is disabled at end of tegra_mipi_calibrate and is re-enabled
>>> during tegra_mipi_wait.
>>>
>>> I think I should fix this to keep the clock enabled till calibration
>>> results are latched.
>>>
>>> All consumers of tegra_mipi_calibrate() will call tegra_mipi_wait().
>>>
>>> So will remove clk_disable mipi clk at end of tegra_mipi_calibrate() 
>>> and
>>> clk_enable mipi_clk at beginning of tegra_mipi_wait()
>> Isn't it possible to perform the calibration after enabling CSI and
>> before of starting the sensor streaming?
> Currently this is what I am doing. Triggering calibration start during 
> CSI receiver being ready and then sensor streaming will happen where 
> internal MIPI CAL detects for LP -> HS transition and applies results 
> to pads. So checking for calibration results after sensor stream is 
> enabled

1. Calling tegra_mipi_calibrate() during CSI streaming where CSI pads 
are enabled and receiver is kept ready

2. Start Sensor stream

3. Calling tegra_mipi_wait() to check for MIPI Cal status.

So as mipi cal clk need to be kept enabled till 3rd step, we can enable 
clock during tegra_mipi_calibrate() and leave it enabled and disable it 
in tegra_mipi_wait after status check.