linux-kernel - RE: [PATCH 1/3] drm/display/dp_mst: Don't validate port refs in drm_dp_check_and_send_link

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Message-ID: <CO6PR12MB5489E9906D3A0E81E01663B5FCAB9@CO6PR12MB5489.namprd12.prod.outlook.com>
Date:   Mon, 13 Jun 2022 09:54:52 +0000
From:   "Lin, Wayne" <Wayne.Lin@....com>
To:     Lyude Paul <lyude@...hat.com>,
        "dri-devel@...ts.freedesktop.org" <dri-devel@...ts.freedesktop.org>
CC:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        Jani Nikula <jani.nikula@...el.com>,
        "Lakha, Bhawanpreet" <Bhawanpreet.Lakha@....com>,
        Rajkumar Subbiah <rsubbia@...eaurora.org>,
        open list <linux-kernel@...r.kernel.org>
Subject: RE: [PATCH 1/3] drm/display/dp_mst: Don't validate port refs in
 drm_dp_check_and_send_link_address()

[Public]

Thanks, Lyude.

Feel free to add
Reviewed-by: Wayne Lin <Wayne.Lin@....com>

> -----Original Message-----
> From: Lyude Paul <lyude@...hat.com>
> Sent: Friday, June 3, 2022 4:18 AM
> To: dri-devel@...ts.freedesktop.org
> Cc: David Airlie <airlied@...ux.ie>; Daniel Vetter <daniel@...ll.ch>; Thomas
> Zimmermann <tzimmermann@...e.de>; Lin, Wayne
> <Wayne.Lin@....com>; Jani Nikula <jani.nikula@...el.com>; Lakha,
> Bhawanpreet <Bhawanpreet.Lakha@....com>; Rajkumar Subbiah
> <rsubbia@...eaurora.org>; open list <linux-kernel@...r.kernel.org>
> Subject: [PATCH 1/3] drm/display/dp_mst: Don't validate port refs in
> drm_dp_check_and_send_link_address()
> 
> Drive-by cleanup, we don't need to validate the port references here as we
> already previously went through the effort of refactoring things such that
> we're guaranteed to be able to access ->mstb and ->port safely from
> drm_dp_check_and_send_link_address(), since the only two places in the
> codebase that drop an MST reference in such a way that it would remove it
> from the topology are both protected under probe_lock.
> 
> Thanks for that, past Lyude!
> 
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> ---
>  drivers/gpu/drm/display/drm_dp_mst_topology.c | 22 +++++--------------
>  1 file changed, 6 insertions(+), 16 deletions(-)
> 
> diff --git a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> index 67b3b9697da7..d84673b3294b 100644
> --- a/drivers/gpu/drm/display/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/display/drm_dp_mst_topology.c
> @@ -2666,24 +2666,14 @@ static int
> drm_dp_check_and_send_link_address(struct drm_dp_mst_topology_mgr
> *mg
>  	}
> 
>  	list_for_each_entry(port, &mstb->ports, next) {
> -		struct drm_dp_mst_branch *mstb_child = NULL;
> -
> -		if (port->input || !port->ddps)
> +		if (port->input || !port->ddps || !port->mstb)
>  			continue;
> 
> -		if (port->mstb)
> -			mstb_child =
> drm_dp_mst_topology_get_mstb_validated(
> -			    mgr, port->mstb);
> -
> -		if (mstb_child) {
> -			ret = drm_dp_check_and_send_link_address(mgr,
> -								 mstb_child);
> -			drm_dp_mst_topology_put_mstb(mstb_child);
> -			if (ret == 1)
> -				changed = true;
> -			else if (ret < 0)
> -				return ret;
> -		}
> +		ret = drm_dp_check_and_send_link_address(mgr, port-
> >mstb);
> +		if (ret == 1)
> +			changed = true;
> +		else if (ret < 0)
> +			return ret;
>  	}
> 
>  	return changed;
> --
> 2.35.3

--
Regards,
Wayne