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

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Date:   Fri, 17 Jul 2020 08:41:58 -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 7/17/20 8:01 AM, Dmitry Osipenko wrote:
> 17.07.2020 07:46, Sowjanya Komatineni пишет:
> ...
>> Looks like sequence posted in TRM need to be updated clearly for proper
>> MIPI CAL start and wait.
>>
>> Correct steps should be like below
>>
>> 1. Set up CSI registers for use case such as number of lanes, virtual
>> channel, etc.
>> 2. Initialize and power up CSI CIL interface
>> 3. Program MIPI CAL bias pads, cal configs, cal control registers and
>> enable calibration start
>> 4. Power up camera through the I2C interface and start sensor streaming
>> through the I2C
>>
>> Note: All sensors might not leave pads in LP-11 state as sensor may be
>> power down when not in use.
>>
>> So start streaming prior to checking for calibration done status as
>> LP-11 -> HS transition happens during sensor stream and calibration
>> logic can apply results to pads and update done status,
>>
>> 5. Wait for done signal from calibration logic
>>
>> 6. perform frame capture thru VI
>> 7. Frame done, CSI goes back to stop state, LP11
>>
>> Will work internally to correct sequence in TRM ...
> Will be nice to have an updated TRM, thank you!
>
> Also, what about the auto-calibration? Isn't it needed to be enabled for
> CSI?
STARTCAL does one time calibration and with AUTOCAL calibration will be 
triggered periodically.

For pads PULLUP/PULLDN/TERM impedance calibration, we only need one-time 
calibration on pads power up.

We always use one time pads calibration for CSI.

>
>> In mipi driver will update as below to have mipi clk enabled till
>> calibration status check is done.
>>
>> Always tegra_mipi_wait() followes tegra_mipi_calibrate() in both DSI and
>> CSI. So below sequence should work good.
>>
>> tegra_mipi_calibrate()
>>
>> - clk_enable mipi cal
>> - program mipi cal registers (bias pads cfgs, mipi cal ctrl and trigger
>> calibration start)
>>
>> tegra_mipi_wait()
>> - read mipi cal status and wait for active and done bits
>> - clk_disable mipi cal
>
> Maybe then it should be better to rename the functions like this:
>
> tegra_mipi_calibrate() -> tegra_mipi_start_calibration()
> tegra_mipi_wait()      -> tegra_mipi_finish_calibration().
>
> and there also should be tegra_mipi_cancel_calibration().
>
>
> Example:
>
> 	tegra_mipi_start_calibration();
>
> 	ret = v4l2_subdev_call(subdev, video, s_stream, on);
> 	if (ret < 0) {
> 		tegra_mipi_cancel_calibration();
> 		goto err;
> 	}
>
> 	tegra_mipi_finish_calibration();
>
>