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

[Jammy Huang <jammy_huang@xxxxxxxxxxxxxx>]

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@xxxxxxxxxxxxxx>
> > ---
> >   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