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

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Message-ID: <1c12e40e-de7f-0599-a941-82760b4c7668@gmail.com>
Date:   Wed, 5 Aug 2020 19:57:54 +0300
From:   Dmitry Osipenko <digetx@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.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

05.08.2020 19:50, Sowjanya Komatineni пишет:
> 
> On 8/5/20 9:47 AM, Dmitry Osipenko wrote:
>> 05.08.2020 19:33, Sowjanya Komatineni пишет:
>>> On 8/5/20 7:19 AM, Dmitry Osipenko wrote:
>>>> 05.08.2020 17:05, Dmitry Osipenko пишет:
>>>>> 05.08.2020 16:46, Thierry Reding пишет:
>>>>>> On Mon, Aug 03, 2020 at 08:42:24AM -0700, Sowjanya Komatineni wrote:
>>>>>>> With the split of MIPI calibration into tegra_mipi_calibrate() and
>>>>>>> tegra_mipi_wait(), MIPI clock is not kept enabled till the
>>>>>>> calibration
>>>>>>> is done.
>>>>>>>
>>>>>>> So, this patch skips disabling MIPI clock after triggering start of
>>>>>>> calibration and disables it only after waiting for done status from
>>>>>>> the calibration logic.
>>>>>>>
>>>>>>> This patch renames tegra_mipi_calibrate() as
>>>>>>> tegra_mipi_start_calibration()
>>>>>>> and tegra_mipi_wait() as tegra_mipi_finish_calibration() to be
>>>>>>> inline
>>>>>>> with their usage.
>>>>>>>
>>>>>>> As MIPI clock is left enabled and in case of any failures with CSI
>>>>>>> input
>>>>>>> streaming tegra_mipi_finish_calibration() will not get invoked.
>>>>>>> So added new API tegra_mipi_cancel_calibration() which disables
>>>>>>> MIPI clock
>>>>>>> and consumer drivers can call this in such cases.
>>>>>>>
>>>>>>> Reviewed-by: Dmitry Osipenko <digetx@...il.com>
>>>>>>> Signed-off-by: Sowjanya Komatineni <skomatineni@...dia.com>
>>>>>>> ---
>>>>>>>    drivers/gpu/drm/tegra/dsi.c |  4 ++--
>>>>>>>    drivers/gpu/host1x/mipi.c   | 19 ++++++++++---------
>>>>>>>    include/linux/host1x.h      |  5 +++--
>>>>>>>    3 files changed, 15 insertions(+), 13 deletions(-)
>>>>>>>
>>>>>>> diff --git a/drivers/gpu/drm/tegra/dsi.c
>>>>>>> b/drivers/gpu/drm/tegra/dsi.c
>>>>>>> index 3820e8d..a7864e9 100644
>>>>>>> --- a/drivers/gpu/drm/tegra/dsi.c
>>>>>>> +++ b/drivers/gpu/drm/tegra/dsi.c
>>>>>>> @@ -694,11 +694,11 @@ static int tegra_dsi_pad_calibrate(struct
>>>>>>> tegra_dsi *dsi)
>>>>>>>            DSI_PAD_PREEMP_PD(0x03) | DSI_PAD_PREEMP_PU(0x3);
>>>>>>>        tegra_dsi_writel(dsi, value, DSI_PAD_CONTROL_3);
>>>>>>>    -    err = tegra_mipi_calibrate(dsi->mipi);
>>>>>>> +    err = tegra_mipi_start_calibration(dsi->mipi);
>>>>>>>        if (err < 0)
>>>>>>>            return err;
>>>>>>>    -    return tegra_mipi_wait(dsi->mipi);
>>>>>>> +    return tegra_mipi_finish_calibration(dsi->mipi);
>>>>>>>    }
>>>>>>>      static void tegra_dsi_set_timeout(struct tegra_dsi *dsi,
>>>>>>> unsigned long bclk,
>>>>>>> diff --git a/drivers/gpu/host1x/mipi.c b/drivers/gpu/host1x/mipi.c
>>>>>>> index e606464..b15ab6e 100644
>>>>>>> --- a/drivers/gpu/host1x/mipi.c
>>>>>>> +++ b/drivers/gpu/host1x/mipi.c
>>>>>>> @@ -293,17 +293,19 @@ int tegra_mipi_disable(struct
>>>>>>> tegra_mipi_device *dev)
>>>>>>>    }
>>>>>>>    EXPORT_SYMBOL(tegra_mipi_disable);
>>>>>>>    -int tegra_mipi_wait(struct tegra_mipi_device *device)
>>>>>>> +void tegra_mipi_cancel_calibration(struct tegra_mipi_device
>>>>>>> *device)
>>>>>>> +{
>>>>>>> +    clk_disable(device->mipi->clk);
>>>>>> Do we need to do anything with the MIPI_CAL_CTRL and MIPI_CAL_STATUS
>>>>>> registers here? We don't clear the START bit in the former when the
>>>>>> calibration has successfully finished, but I suspect that's because
>>>>>> the bit is self-clearing. But I wonder if we still need to clear it
>>>>>> upon cancellation to make sure the calibration does indeed stop.
>>>>> Apparently there is no way to explicitly stop calibration other
>>>>> than to
>>>>> reset MIPI calibration block, but Sowjanya says this is unnecessary.
>>>>>
>>>>> Perhaps having a fixed delay before disabling clock could be enough to
>>>>> ensure that calibration is stopped before the clock is disabled?
>>>>>
>>>> Actually, there is a MIPI_CAL_ACTIVE bit in the status register. Maybe
>>>> it needs to be polled until it's unset?
>>> Confirmed with HW design team during this patch update.
>>>
>>> SW does not need to clear START bit and only write 1 takes effect to
>>> that bit.
>>>
>>> Also, no need to have delay or do any other register settings unclear as
>>> its FSM and there's nothing to get stuck.
>>>
>>> Also it goes thru small finite set of codes and by the time sensor
>>> programming happens for enabling streaming FSM will finish its
>>> calibration sequence much early and it will only wait for pads LP-11.
>>>
>>> So, during cancel we only need disable MIPI clock.
>>>
>> But there is no guarantee that cancel_calibration() couldn't be invoked
>> in the middle of the calibration process, hence FSM could freeze in an
>> intermediate state if it's running on the disabled MIPI clock, this
>> doesn't sound good.
> Actual calibration logic uses UART_FST_CAL clock which is always enabled

What enables the UART_FST_CAL clock? I don't see this clock used anywhere.