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

From: Sowjanya Komatineni <skomatineni@nvidia.com>
To: Dmitry Osipenko <digetx@gmail.com>,
	Thierry Reding <thierry.reding@gmail.com>
Cc: <jonathanh@nvidia.com>, <frankc@nvidia.com>, <hverkuil@xs4all.nl>,
	<sakari.ailus@iki.fi>, <robh+dt@kernel.org>,
	<helen.koike@collabora.com>, <gregkh@linuxfoundation.org>,
	<linux-media@vger.kernel.org>, <devicetree@vger.kernel.org>,
	<linux-tegra@vger.kernel.org>, <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH v8 08/10] gpu: host1x: mipi: Keep MIPI clock enabled till calibration is done
Date: Wed, 5 Aug 2020 10:46:03 -0700	[thread overview]
Message-ID: <b2098a68-d02f-b406-fc57-56e3ff5d8d1a@nvidia.com> (raw)
In-Reply-To: <0e78c5ca-c529-1e98-891d-30351c9aae81@gmail.com>

On 8/5/20 10:34 AM, Dmitry Osipenko wrote:
> 05.08.2020 20:29, Sowjanya Komatineni пишет:
> ...
>> UART_FST_MIPI_CAL is the clock used for calibration logic which is FSM
>> that goes thru sequence codes and when done waits for pads to be in
>> LP-11 to apply results.
>>
>> MIPI_CLK is controller gate clock which is also need to be kept enabled
>> as incase if it sees LP-11 it updates registers so its recommended to
>> have this clock enabled.
>>
>> We can cancel_calibration() in CSI only when csi/sensor stream on fails
>> and in which case there will be no LP-11 so we can unconditionally
>> disable MIPI_CLK.
>>
> There is no guarantee that the fail comes before the LP-11. For example,
> some odd camera driver may have a complicated enable sequence which may
> fail after enabling the hardware streaming.

MIPI_CLK to keep enable is for calibration logic to update results, but 
like I said calibration logic uses UART_FST_MIPI_CAL clock. So even in 
case if fail happens from sensor after having pads in LP-11 then, 
calibration logic will still be running but result update will not 
happen with clock disabled. But HW will not stuck as this is confirmed 
from HW designer.