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

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Message-ID: <d285566b-ed7c-8e2a-a078-7bdd5bac13e3@aspeedtech.com>
Date:   Tue, 25 Apr 2023 15:39:06 +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,

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