linux-kernel - Re: [PATCH v2 2/4 RESEND] gpu/drm: tegra: dsi: move prepare function to the top of encoder enable

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Message-ID: <7012249.lOV4Wx5bFT@senjougahara>
Date: Thu, 15 Jan 2026 14:47:36 +0900
From: Mikko Perttunen <mperttunen@...dia.com>
To: Rob Herring <robh@...nel.org>, Krzysztof Kozlowski <krzk+dt@...nel.org>,
 Conor Dooley <conor+dt@...nel.org>,
 Thierry Reding <thierry.reding@...il.com>,
 Thierry Reding <treding@...dia.com>, Jonathan Hunter <jonathanh@...dia.com>,
 Prashant Gaikwad <pgaikwad@...dia.com>,
 Michael Turquette <mturquette@...libre.com>, Stephen Boyd <sboyd@...nel.org>,
 David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>,
 Svyatoslav Ryhel <clamor95@...il.com>, Dmitry Osipenko <digetx@...il.com>,
 Charan Pedumuru <charan.pedumuru@...il.com>,
 Svyatoslav Ryhel <clamor95@...il.com>
Cc: devicetree@...r.kernel.org, linux-tegra@...r.kernel.org,
 linux-kernel@...r.kernel.org, linux-clk@...r.kernel.org,
 dri-devel@...ts.freedesktop.org
Subject:
 Re: [PATCH v2 2/4 RESEND] gpu/drm: tegra: dsi: move prepare function to the
 top of encoder enable

On Thursday, December 4, 2025 3:17 PM Svyatoslav Ryhel wrote:
> The tegra_dsi_prepare function performs hardware setup and should be
> called before any register readings or there will be a risk of device
> hangup on register access. To avoid this situation, tegra_dsi_prepare must
> be called at the beginning of tegra_dsi_encoder_enable.
> 
> Signed-off-by: Svyatoslav Ryhel <clamor95@...il.com>
> ---
>  drivers/gpu/drm/tegra/dsi.c | 12 ++++++------
>  1 file changed, 6 insertions(+), 6 deletions(-)
> 
> diff --git a/drivers/gpu/drm/tegra/dsi.c b/drivers/gpu/drm/tegra/dsi.c
> index 278bf2c85524..8e80c7efe8b4 100644
> --- a/drivers/gpu/drm/tegra/dsi.c
> +++ b/drivers/gpu/drm/tegra/dsi.c
> @@ -914,6 +914,12 @@ static void tegra_dsi_encoder_enable(struct drm_encoder *encoder)
>  	u32 value;
>  	int err;
>  
> +	err = tegra_dsi_prepare(dsi);
> +	if (err < 0) {
> +		dev_err(dsi->dev, "failed to prepare: %d\n", err);
> +		return;
> +	}
> +
>  	/* If the bootloader enabled DSI it needs to be disabled
>  	 * in order for the panel initialization commands to be
>  	 * properly sent.
> @@ -923,12 +929,6 @@ static void tegra_dsi_encoder_enable(struct drm_encoder *encoder)
>  	if (value & DSI_POWER_CONTROL_ENABLE)
>  		tegra_dsi_disable(dsi);
>  
> -	err = tegra_dsi_prepare(dsi);
> -	if (err < 0) {
> -		dev_err(dsi->dev, "failed to prepare: %d\n", err);
> -		return;
> -	}
> -
>  	state = tegra_dsi_get_state(dsi);
>  
>  	tegra_dsi_set_timeout(dsi, state->bclk, state->vrefresh);
> 

The section of code before the tegra_dsi_prepare call was removed in 'Revert "drm/tegra: dsi: Clear enable register if powered by bootloader"', so this patch should no longer be necessary.

Mikko