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

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Date:   Wed, 5 Aug 2020 15:46:00 +0200
From:   Thierry Reding <thierry.reding@...il.com>
To:     Sowjanya Komatineni <skomatineni@...dia.com>
Cc:     jonathanh@...dia.com, frankc@...dia.com, hverkuil@...all.nl,
        sakari.ailus@....fi, robh+dt@...nel.org, helen.koike@...labora.com,
        digetx@...il.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 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.

Thierry

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