linux-kernel - Re: [PATCH v2] drm/ast: Fix modeset failed on DisplayPort

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Message-ID: <01973671-55e0-d701-ca38-a583d441a4fc@suse.de>
Date:   Wed, 31 May 2023 12:51:45 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Jammy Huang <jammy_huang@...eedtech.com>, airlied@...hat.com,
        airlied@...il.com, daniel@...ll.ch
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v2] drm/ast: Fix modeset failed on DisplayPort

Hi Jammy

Am 25.05.23 um 03:29 schrieb Jammy Huang:
> If we switch display and update cursor together, it could lead to
> modeset failed because of concurrent access to IO registers.
> 
> Add lock protection in DP's edid access to avoid this problem.
> 
> Signed-off-by: Jammy Huang <jammy_huang@...eedtech.com>
> ---
>   v2 changes:
>    - Fix build error since new struct ast_device is used.
> ---
>   drivers/gpu/drm/ast/ast_mode.c | 11 +++++++++++
>   1 file changed, 11 insertions(+)
> 
> diff --git a/drivers/gpu/drm/ast/ast_mode.c b/drivers/gpu/drm/ast/ast_mode.c
> index 36374828f6c8..9fcbf540d6fc 100644
> --- a/drivers/gpu/drm/ast/ast_mode.c
> +++ b/drivers/gpu/drm/ast/ast_mode.c
> @@ -1647,6 +1647,8 @@ static int ast_dp501_output_init(struct ast_device *ast)
>   static int ast_astdp_connector_helper_get_modes(struct drm_connector *connector)
>   {
>   	void *edid;
> +	struct drm_device *dev = connector->dev;
> +	struct ast_device *ast = to_ast_device(dev);
>   
>   	int succ;
>   	int count;
> @@ -1655,10 +1657,18 @@ static int ast_astdp_connector_helper_get_modes(struct drm_connector *connector)
>   	if (!edid)
>   		goto err_drm_connector_update_edid_property;
>   
> +	/*
> +	 * Protect access to I/O registers from concurrent modesetting
> +	 * by acquiring the I/O-register lock.
> +	 */
> +	mutex_lock(&ast->ioregs_lock);
> +
>   	succ = ast_astdp_read_edid(connector->dev, edid);
>   	if (succ < 0)
>   		goto err_kfree;
>   
> +	mutex_unlock(&ast->ioregs_lock);
> +
>   	drm_connector_update_edid_property(connector, edid);
>   	count = drm_add_edid_modes(connector, edid);
>   	kfree(edid);
> @@ -1666,6 +1676,7 @@ static int ast_astdp_connector_helper_get_modes(struct drm_connector *connector)
>   	return count;
>   
>   err_kfree:

This label needs to be named 'err_mutex_unlock' please. With that fixed, 
you can add

Reviewed-by: Thomas Zimmermann <tzimmermann@...e.de>

Best regards
Thomas

> +	mutex_unlock(&ast->ioregs_lock);
>   	kfree(edid);
>   err_drm_connector_update_edid_property:
>   	drm_connector_update_edid_property(connector, NULL);
> 
> base-commit: 933174ae28ba72ab8de5b35cb7c98fc211235096

-- 
Thomas Zimmermann
Graphics Driver Developer
SUSE Software Solutions Germany GmbH
Frankenstrasse 146, 90461 Nuernberg, Germany
GF: Ivo Totev, Andrew Myers, Andrew McDonald, Boudien Moerman
HRB 36809 (AG Nuernberg)

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