Received-SPF: pass (google.com: domain of linux-kernel+bounces-129434-linux.lists.archive=gmail.com@vger.kernel.org designates 2604:1380:45e3:2400::1 as permitted sender) client-ip=2604:1380:45e3:2400::1;
Message-ID: <15e15564-66f5-4057-8b6f-9361e4b76e76@suse.de>
Date: Wed, 3 Apr 2024 11:32:49 +0200
Precedence: bulk
MIME-Version: 1.0
User-Agent: Mozilla Thunderbird
Subject: Re: [PATCH v2] drm/ast: Fix soft lockup
To: Jammy Huang <jammy_huang@aspeedtech.com>, jfalempe@redhat.com,
 maarten.lankhorst@linux.intel.com, mripard@kernel.org, airlied@redhat.com,
 airlied@gmail.com, daniel@ffwll.ch
Cc: dri-devel@lists.freedesktop.org, linux-kernel@vger.kernel.org
References: <20240403090246.1495487-1-jammy_huang@aspeedtech.com>
Content-Language: en-US
From: Thomas Zimmermann <tzimmermann@suse.de>
Autocrypt: addr=tzimmermann@suse.de; keydata=
 xsBNBFs50uABCADEHPidWt974CaxBVbrIBwqcq/WURinJ3+2WlIrKWspiP83vfZKaXhFYsdg
 XH47fDVbPPj+d6tQrw5lPQCyqjwrCPYnq3WlIBnGPJ4/jreTL6V+qfKRDlGLWFjZcsrPJGE0
 BeB5BbqP5erN1qylK9i3gPoQjXGhpBpQYwRrEyQyjuvk+Ev0K1Jc5tVDeJAuau3TGNgah4Yc
 hdHm3bkPjz9EErV85RwvImQ1dptvx6s7xzwXTgGAsaYZsL8WCwDaTuqFa1d1jjlaxg6+tZsB
 9GluwvIhSezPgnEmimZDkGnZRRSFiGP8yjqTjjWuf0bSj5rUnTGiyLyRZRNGcXmu6hjlABEB
 AAHNJ1Rob21hcyBaaW1tZXJtYW5uIDx0emltbWVybWFubkBzdXNlLmRlPsLAjgQTAQgAOAIb
 AwULCQgHAgYVCgkICwIEFgIDAQIeAQIXgBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftODH
 AAoJEGgNwR1TC3ojx1wH/0hKGWugiqDgLNXLRD/4TfHBEKmxIrmfu9Z5t7vwUKfwhFL6hqvo
 lXPJJKQpQ2z8+X2vZm/slsLn7J1yjrOsoJhKABDi+3QWWSGkaGwRJAdPVVyJMfJRNNNIKwVb
 U6B1BkX2XDKDGffF4TxlOpSQzdtNI/9gleOoUA8+jy8knnDYzjBNOZqLG2FuTdicBXblz0Mf
 vg41gd9kCwYXDnD91rJU8tzylXv03E75NCaTxTM+FBXPmsAVYQ4GYhhgFt8S2UWMoaaABLDe
 7l5FdnLdDEcbmd8uLU2CaG4W2cLrUaI4jz2XbkcPQkqTQ3EB67hYkjiEE6Zy3ggOitiQGcqp
 j//OwE0EWznS4AEIAMYmP4M/V+T5RY5at/g7rUdNsLhWv1APYrh9RQefODYHrNRHUE9eosYb
 T6XMryR9hT8XlGOYRwKWwiQBoWSDiTMo/Xi29jUnn4BXfI2px2DTXwc22LKtLAgTRjP+qbU6
 3Y0xnQN29UGDbYgyyK51DW3H0If2a3JNsheAAK+Xc9baj0LGIc8T9uiEWHBnCH+RdhgATnWW
 GKdDegUR5BkDfDg5O/FISymJBHx2Dyoklv5g4BzkgqTqwmaYzsl8UxZKvbaxq0zbehDda8lv
 hFXodNFMAgTLJlLuDYOGLK2AwbrS3Sp0AEbkpdJBb44qVlGm5bApZouHeJ/+n+7r12+lqdsA
 EQEAAcLAdgQYAQgAIAIbDBYhBHIX+6yM6c9jRKFo5WgNwR1TC3ojBQJftOH6AAoJEGgNwR1T
 C3ojVSkIALpAPkIJPQoURPb1VWjh34l0HlglmYHvZszJWTXYwavHR8+k6Baa6H7ufXNQtThR
 yIxJrQLW6rV5lm7TjhffEhxVCn37+cg0zZ3j7zIsSS0rx/aMwi6VhFJA5hfn3T0TtrijKP4A
 SAQO9xD1Zk9/61JWk8OysuIh7MXkl0fxbRKWE93XeQBhIJHQfnc+YBLprdnxR446Sh8Wn/2D
 Ya8cavuWf2zrB6cZurs048xe0UbSW5AOSo4V9M0jzYI4nZqTmPxYyXbm30Kvmz0rYVRaitYJ
 4kyYYMhuULvrJDMjZRvaNe52tkKAvMevcGdt38H4KSVXAylqyQOW5zvPc4/sq9c=
In-Reply-To: <20240403090246.1495487-1-jammy_huang@aspeedtech.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit


Am 03.04.24 um 11:02 schrieb Jammy Huang:
> There is a while-loop in ast_dp_set_on_off() that could lead to
> infinite-loop. This is because the register, VGACRI-Dx, checked in
> this API is a scratch register actually controlled by a MCU, named
> DPMCU, in BMC.
>
> These scratch registers are protected by scu-lock. If suc-lock is not
> off, DPMCU can not update these registers and then host will have soft
> lockup due to never updated status.
>
> DPMCU is used to control DP and relative registers to handshake with
> host's VGA driver. Even the most time-consuming task, DP's link
> training, is less than 100ms. 200ms should be enough.
>
> Signed-off-by: Jammy Huang <jammy_huang@aspeedtech.com>
> Reviewed-by: Jocelyn Falempe <jfalempe@redhat.com>

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

> ---
>   drivers/gpu/drm/ast/ast_dp.c | 3 +++
>   1 file changed, 3 insertions(+)
>
> diff --git a/drivers/gpu/drm/ast/ast_dp.c b/drivers/gpu/drm/ast/ast_dp.c
> index ebb6d8ebd44e..1e9259416980 100644
> --- a/drivers/gpu/drm/ast/ast_dp.c
> +++ b/drivers/gpu/drm/ast/ast_dp.c
> @@ -180,6 +180,7 @@ void ast_dp_set_on_off(struct drm_device *dev, bool on)
>   {
>   	struct ast_device *ast = to_ast_device(dev);
>   	u8 video_on_off = on;
> +	u32 i = 0;
>   
>   	// Video On/Off
>   	ast_set_index_reg_mask(ast, AST_IO_VGACRI, 0xE3, (u8) ~AST_DP_VIDEO_ENABLE, on);
> @@ -192,6 +193,8 @@ void ast_dp_set_on_off(struct drm_device *dev, bool on)
>   						ASTDP_MIRROR_VIDEO_ENABLE) != video_on_off) {
>   			// wait 1 ms
>   			mdelay(1);
> +			if (++i > 200)
> +				break;
>   		}
>   	}
>   }
>
> base-commit: b0546776ad3f332e215cebc0b063ba4351971cca

-- 
--
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)