linux-kernel - Re: [PATCH 4.9 087/116] drm/dp_mst: Remove VCPI while disabling topology mgr

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Message-ID: <6fa270d0d395d87c41b7d0a9ec87eadea5398eb6.camel@redhat.com>
Date:   Fri, 14 Feb 2020 12:38:44 -0500
From:   Lyude Paul <lyude@...hat.com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-kernel@...r.kernel.org
Cc:     stable@...r.kernel.org, Wayne Lin <Wayne.Lin@....com>,
        Sasha Levin <sashal@...nel.org>
Subject: Re: [PATCH 4.9 087/116] drm/dp_mst: Remove VCPI while disabling
 topology mgr

We should drop this and the versions for all of the other kernel versions.
This patch later got reverted in a86675968e2300fb567994459da3dbc4cd1b322a in
drm-misc/drm-misc-next, and then replaced with a proper fix in
8732fe46b20c951493bfc4dba0ad08efdf41de81

On Thu, 2020-02-13 at 07:20 -0800, Greg Kroah-Hartman wrote:
> From: Wayne Lin <Wayne.Lin@....com>
> 
> [ Upstream commit 64e62bdf04ab8529f45ed0a85122c703035dec3a ]
> 
> [Why]
> 
> This patch is trying to address the issue observed when hotplug DP
> daisy chain monitors.
> 
> e.g.
> src-mstb-mstb-sst -> src (unplug) mstb-mstb-sst -> src-mstb-mstb-sst
> (plug in again)
> 
> Once unplug a DP MST capable device, driver will call
> drm_dp_mst_topology_mgr_set_mst() to disable MST. In this function,
> it cleans data of topology manager while disabling mst_state. However,
> it doesn't clean up the proposed_vcpis of topology manager.
> If proposed_vcpi is not reset, once plug in MST daisy chain monitors
> later, code will fail at checking port validation while trying to
> allocate payloads.
> 
> When MST capable device is plugged in again and try to allocate
> payloads by calling drm_dp_update_payload_part1(), this
> function will iterate over all proposed virtual channels to see if
> any proposed VCPI's num_slots is greater than 0. If any proposed
> VCPI's num_slots is greater than 0 and the port which the
> specific virtual channel directed to is not in the topology, code then
> fails at the port validation. Since there are stale VCPI allocations
> from the previous topology enablement in proposed_vcpi[], code will fail
> at port validation and reurn EINVAL.
> 
> [How]
> 
> Clean up the data of stale proposed_vcpi[] and reset mgr->proposed_vcpis
> to NULL while disabling mst in drm_dp_mst_topology_mgr_set_mst().
> 
> Changes since v1:
> *Add on more details in commit message to describe the issue which the
> patch is trying to fix
> 
> Signed-off-by: Wayne Lin <Wayne.Lin@....com>
> [added cc to stable]
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> Link: 
> https://patchwork.freedesktop.org/patch/msgid/20191205090043.7580-1-Wayne.Lin@amd.com
> Cc: <stable@...r.kernel.org> # v3.17+
> Signed-off-by: Sasha Levin <sashal@...nel.org>
> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 12 ++++++++++++
>  1 file changed, 12 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c
> b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 17aedaaf364c1..8b1d497b7f99f 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2042,6 +2042,7 @@ static bool drm_dp_get_vc_payload_bw(int dp_link_bw,
>  int drm_dp_mst_topology_mgr_set_mst(struct drm_dp_mst_topology_mgr *mgr,
> bool mst_state)
>  {
>  	int ret = 0;
> +	int i = 0;
>  	struct drm_dp_mst_branch *mstb = NULL;
>  
>  	mutex_lock(&mgr->lock);
> @@ -2106,10 +2107,21 @@ int drm_dp_mst_topology_mgr_set_mst(struct
> drm_dp_mst_topology_mgr *mgr, bool ms
>  		/* this can fail if the device is gone */
>  		drm_dp_dpcd_writeb(mgr->aux, DP_MSTM_CTRL, 0);
>  		ret = 0;
> +		mutex_lock(&mgr->payload_lock);
>  		memset(mgr->payloads, 0, mgr->max_payloads * sizeof(struct
> drm_dp_payload));
>  		mgr->payload_mask = 0;
>  		set_bit(0, &mgr->payload_mask);
> +		for (i = 0; i < mgr->max_payloads; i++) {
> +			struct drm_dp_vcpi *vcpi = mgr->proposed_vcpis[i];
> +
> +			if (vcpi) {
> +				vcpi->vcpi = 0;
> +				vcpi->num_slots = 0;
> +			}
> +			mgr->proposed_vcpis[i] = NULL;
> +		}
>  		mgr->vcpi_mask = 0;
> +		mutex_unlock(&mgr->payload_lock);
>  	}
>  
>  out_unlock:
-- 
Cheers,
	Lyude Paul (she/her)
	Associate Software Engineer at Red Hat