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 15:49:35 -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 2:18 PM, Dmitry Osipenko wrote:
> 17.07.2020 00:09, Sowjanya Komatineni пишет:
>> On 7/16/20 1:38 PM, Dmitry Osipenko wrote:
>>> 15.07.2020 07:20, Sowjanya Komatineni пишет:
>>>> SW can trigger MIPI pads calibration any time after power on
>>>> but calibration results will be latched and applied to the pads
>>>> by MIPI CAL unit only when the link is in LP-11 state and then
>>>> status register will be updated.
>>>>
>>>> For CSI, trigger of pads calibration happen during CSI stream
>>>> enable where CSI receiver is kept ready prior to sensor or CSI
>>>> transmitter stream start.
>>>>
>>>> So, pads may not be in LP-11 at this time and waiting for the
>>>> calibration to be done immediate after calibration start will
>>>> result in timeout.
>>>>
>>>> This patch splits tegra_mipi_calibrate() and tegra_mipi_wait()
>>>> so triggering for calibration and waiting for it to complete can
>>>> happen at different stages.
>>>>
>>>> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
>>>> ---
>>> ...
>>>>    int tegra_mipi_calibrate(struct tegra_mipi_device *device)
>>>>    {
>>>> @@ -370,12 +381,10 @@ int tegra_mipi_calibrate(struct
>>>> tegra_mipi_device *device)
>>>>        value |= MIPI_CAL_CTRL_START;
>>>>        tegra_mipi_writel(device->mipi, value, MIPI_CAL_CTRL);
>>>>    -    err = tegra_mipi_wait(device->mipi);
>>> Doesn't MIPI clock need to be enabled during of the calibration process?
>> MIPI clock is already enabled in tegra_mipi_calibrate
>>>>        mutex_unlock(&device->mipi->lock);
>>>>        clk_disable(device->mipi->clk);
> 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()

>
>>>>    -    return err;
>>>> +    return 0;
>>>>    }
>>>>    EXPORT_SYMBOL(tegra_mipi_calibrate);