linux-kernel - Re: [PATCH] drm/dp_mst: Don't drop NAKs for down responses

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Message-ID: <CAMavQKKvxrYdi5RfsexT=01KonqEaB-_8VompN4vbexY9gL2mA@mail.gmail.com>
Date:   Mon, 6 Apr 2020 15:50:14 -0400
From:   Sean Paul <sean@...rly.run>
To:     Lyude Paul <lyude@...hat.com>
Cc:     dri-devel <dri-devel@...ts.freedesktop.org>,
        Wayne Lin <Wayne.Lin@....com>, Wayne Lin <waynelin@....com>,
        Sean Paul <seanpaul@...omium.org>,
        Maarten Lankhorst <maarten.lankhorst@...ux.intel.com>,
        Maxime Ripard <mripard@...nel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/dp_mst: Don't drop NAKs for down responses

On Fri, Apr 3, 2020 at 4:03 PM Lyude Paul <lyude@...hat.com> wrote:
>
> It looks like that when we introduced the ability to handle multiple
> down requests at once, we accidentally started dropping NAK replies -
> causing sideband messages which got NAK'd to seemingly timeout and cause
> all sorts of weirdness.
>
> So, fix this by making sure we don't return from
> drm_dp_mst_handle_down_rep() early, but instead treat NAKs like any
> other message.
>
> Signed-off-by: Lyude Paul <lyude@...hat.com>
> Fixes: fbc821c4a506 ("drm/mst: Support simultaneous down replies")
> Cc: Wayne Lin <Wayne.Lin@....com>
> Cc: Wayne Lin <waynelin@....com>
> Cc: Sean Paul <seanpaul@...omium.org>

Thank you for fixing this

Reviewed-by: Sean Paul <sean@...rly.run>

> ---
>  drivers/gpu/drm/drm_dp_mst_topology.c | 1 -
>  1 file changed, 1 deletion(-)
>
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 10d0315af513..5449ada3e019 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -3813,7 +3813,6 @@ static int drm_dp_mst_handle_down_rep(struct drm_dp_mst_topology_mgr *mgr)
>                               txmsg->reply.u.nak.reason,
>                               drm_dp_mst_nak_reason_str(txmsg->reply.u.nak.reason),
>                               txmsg->reply.u.nak.nak_data);
> -               goto out_clear_reply;
>         }
>
>         memset(msg, 0, sizeof(struct drm_dp_sideband_msg_rx));
> --
> 2.25.1
>