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 20:18:12 -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 8:14 PM, Sowjanya Komatineni wrote:
>
> 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
>
Based on internal design check from designer, as long as its in waiting 
for LP-11 stage, next calibration request can be triggered again but 
ACTIVE bit we will see it at 1. So we should check for DONE bits to 
confirm if calibration is done or not.

To start next calibration, it can take effect as long as its in wait for 
LP-11 mode.

>>
>>