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

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Message-ID: <2f516118-2183-400f-7efd-04c2766fa9d6@suse.de>
Date:   Wed, 24 May 2023 12:47:35 +0200
From:   Thomas Zimmermann <tzimmermann@...e.de>
To:     Jammy Huang <jammy_huang@...eedtech.com>, airlied@...hat.com
Cc:     linux-kernel@...r.kernel.org, dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH] drm/ast: Fix modeset failed on DisplayPort

Hi,

this patch also fell through the cracks. Apologies.

Am 24.05.23 um 04:29 schrieb Jammy Huang:
> Hi Thomas,
> 
> Do you have other suggestion for this patch??

The main issue was that struct ast_private is now called struct 
ast_device.  So the current patch cannot be applied.

> 
> Please kindly advise.
> 
> On 2023/4/25 下午 03:39, Jammy Huang wrote:
>> Hi Thomas,
>>
>> I think DP501 is OK. It doesn't use ioregs in ast_dp501_read_edid().
>>
>> On 2023/4/25 下午 03:27, Thomas Zimmermann wrote:
>>> 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:

Here's a minor issue that the goto label should now be called 
err_mutex_unlock.

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: 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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