linux-kernel - Re: [PATCH v9 08/10] gpu: host1x: mipi: Keep MIPI clock enabled and mutex locked till calibration done

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Date:   Thu, 6 Aug 2020 20:14:41 -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:     <gregkh@...uxfoundation.org>, <linux-media@...r.kernel.org>,
        <devicetree@...r.kernel.org>, <linux-tegra@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v9 08/10] gpu: host1x: mipi: Keep MIPI clock enabled and
 mutex locked till calibration done


On 8/6/20 8:10 PM, Sowjanya Komatineni wrote:
>
> On 8/6/20 7:31 PM, Dmitry Osipenko wrote:
>> 06.08.2020 22:01, Sowjanya Komatineni пишет:
>> ...
>>> +int tegra_mipi_start_calibration(struct tegra_mipi_device *device)
>>>   {
>>>       const struct tegra_mipi_soc *soc = device->mipi->soc;
>>>       unsigned int i;
>>> @@ -381,12 +375,16 @@ int tegra_mipi_calibrate(struct 
>>> tegra_mipi_device *device)
>>>       value |= MIPI_CAL_CTRL_START;
>>>       tegra_mipi_writel(device->mipi, value, MIPI_CAL_CTRL);
>>>   -    mutex_unlock(&device->mipi->lock);
>>> -    clk_disable(device->mipi->clk);
>>> +    /*
>>> +     * Wait for min 72uS to let calibration logic finish calibration
>>> +     * sequence codes before waiting for pads idle state to apply the
>>> +     * results.
>>> +     */
>>> +    usleep_range(75, 80);
>> Could you please explain why the ACTIVE bit can't be polled instead of
>> using the fixed delay? Doesn't ACTIVE bit represents the state of the
>> busy FSM?
>
> Based on internal discussion, ACTIVE bit gets cleared when all enabled 
> pads calibration is done (same time as when DONE set to 1).
>
> Will request HW designer to look into design and confirm  exactly when 
> ACTIVE bit gets cleared.
>
> Will get back on this.
>
Verified with HW designer. above is correct. ACTIVE bit update happens 
same time as DONE bit.

Active = !(DONE)

In case of calibration logic waiting for LP-11 where done bit does not 
get set, ACTIVE will still be 1 and on next start trigger new 
calibration will start

>
>