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

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Date:   Tue, 25 Apr 2023 09:27:04 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Jammy Huang <jammy_huang@...eedtech.com>, airlied@...hat.com
Cc:     dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/ast: Fix modeset failed on DisplayPort

Hi

Am 25.04.23 um 09:03 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.

Thanks for the patch. I thought I fixed this issue already, but that 
apparently only happened for SIL164 and VGA.

What about ast_dp501_connector_helper_get_modes()? Does it require the 
locking as well?

> 
> Signed-off-by: Jammy Huang <jammy_huang@...eedtech.com>
> ---
>   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 984ec590a7e7..fe5f1fd61361 100644
> --- a/drivers/gpu/drm/ast/ast_mode.c
> +++ b/drivers/gpu/drm/ast/ast_mode.c
> @@ -1635,6 +1635,8 @@ static int ast_dp501_output_init(struct ast_private *ast)
>   static int ast_astdp_connector_helper_get_modes(struct drm_connector *connector)
>   {
>   	void *edid;
> +	struct drm_device *dev = connector->dev;
> +	struct ast_private *ast = to_ast_private(dev);

We've meanwhile renamed ast_private to ast_device. Could you please 
provide an updated patch for the drm-misc-next tree?

Best regards
Thomas

>   
>   	int succ;
>   	int count;
> @@ -1643,10 +1645,18 @@ 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);
> @@ -1654,6 +1664,7 @@ static int ast_astdp_connector_helper_get_modes(struct drm_connector *connector)
>   	return count;
>   
>   err_kfree:
> +	mutex_unlock(&ast->ioregs_lock);
>   	kfree(edid);
>   err_drm_connector_update_edid_property:
>   	drm_connector_update_edid_property(connector, NULL);
> 
> base-commit: 61d325dcbc05d8fef88110d35ef7776f3ac3f68b

-- 
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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