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

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Date:   Wed, 24 May 2023 10:29:57 +0800
From:   Jammy Huang <jammy_huang@...eedtech.com>
To:     Thomas Zimmermann <tzimmermann@...e.de>, <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 Thomas,

Do you have other suggestion for this patch??

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:
>>> +    mutex_unlock(&ast->ioregs_lock);
>>>       kfree(edid);
>>>   err_drm_connector_update_edid_property:
>>>       drm_connector_update_edid_property(connector, NULL);
>>>
>>> base-commit: 61d325dcbc05d8fef88110d35ef7776f3ac3f68b
>>
-- 
Best Regards
Jammy