linux-kernel - Re: [PATCH v8 08/10] gpu: host1x: mipi: Keep MIPI clock enabled till calibration is done

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Message-ID: <3a4be8e9-32a5-e7d8-8727-8d860368bc8e@nvidia.com>
Date:   Thu, 6 Aug 2020 11:51:59 -0700
From:   Sowjanya Komatineni <skomatineni@...dia.com>
To:     Dmitry Osipenko <digetx@...il.com>,
        Thierry Reding <thierry.reding@...il.com>
CC:     <jonathanh@...dia.com>, <frankc@...dia.com>, <hverkuil@...all.nl>,
        <sakari.ailus@....fi>, <robh+dt@...nel.org>,
        <helen.koike@...labora.com>, <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 v8 08/10] gpu: host1x: mipi: Keep MIPI clock enabled till
 calibration is done


On 8/6/20 11:44 AM, Sowjanya Komatineni wrote:
>
> On 8/6/20 11:18 AM, Dmitry Osipenko wrote:
>> 06.08.2020 21:07, Sowjanya Komatineni пишет:
>>> On 8/6/20 11:01 AM, Dmitry Osipenko wrote:
>>>> 06.08.2020 20:52, Sowjanya Komatineni пишет:
>>>> ...
>>>>> Right mutex_unlock should happen at end of finish_calibration.
>>>>>
>>>>> With keeping mutex locked in start, we dont have to check for 
>>>>> active to
>>>>> be 0 to issue start as mutex will keep it locked and other pads
>>>>> calibration can only go thru when current one is done.
>>>>>
>>>>> So instead of below sequence, its simpler to do this way?
>>>>>
>>>>> start_calibration()
>>>>>
>>>>> - mutex_lock
>>>>>
>>>>> - wait for 72uS after start
>>>>>
>>>>> finish_calibration()
>>>>>
>>>>> - keep check for ACTIVE = 0 and DONE = 1
>>>> I think only the DONE bits which correspond to the mipi_device->pads
>>>> bitmask should be awaited.
>>> As next START can't be triggered when auto cal is ACTIVE, we should 
>>> keep
>>> this in finish.
>>>
>>> As we do mutex_unlock only at end of finish, other pads calibrations
>>> dont go thru till the one in process is finished.
>>>
>>> So in this case ACTIVE applies to current selected pads that are under
>>> calibration.
>> Should be better to check only the relevant bits in order to catch bugs,
>> otherwise you may get a DONE status from the irrelevant pads.
> tegra_mipi_device is separate for DSI and CSI channels. mutex lock 
> used during calibrate is device specific lock.
> So, it will not prevent other devices to hold till on going 
> calibration is done unless we add wait for active bit before 
> triggering start.
>
> Currently we wait for active bit at end during calibration done check 
> after start trigger. But when other devices go thru calibration in 
> parallel as lock is device specific and not common lock for all 
> devices it will trigger start but MIPI calibration logic ignore if 
> previous calibration is still in progress.
>
> Need to serialize calibration start requests from different devices 
> based on ACTIVE bit.

Sorry confused. MIPI driver is using common lock from tegra_mipi for all 
tegra_mipi_device

So should be ok as only one device start_calibration can happen at a time.

But its still good to check ACTIVE is cleared and to report as error if 
not as ACTIVE will be cleared once set of pads enabled for this calibration.

Eg: CSI port can be 4 lane and all 4 pads gets enabled at same time and 
with this ACTIVE should still be verified to be 0 to make sure all pads 
calibration is done

>
>>>> Perhaps the start_calibration() also needs to be changed to not touch
>>>> the MIPI_CAL_CONFIG bits of the unrelated pads?
>>> Driver already takes care of programming corresponding pads config 
>>> only.
>> It writes 0 to the config of the unrelated pads, which probably isn't
>> nice if some pads use periodic auto-calibration.
>>
>> https://elixir.bootlin.com/linux/v5.8/source/drivers/gpu/host1x/mipi.c#L350 
>>
>>
>> Although looks like auto-calibration isn't supported by the current 
>> driver.
>
> Yes we don't use auto-calibration.
>
> Only common bit here is MIPI_CAL_CTRL start. All others are pad 
> specific currently.
>