Re: [PATCH v3 2/4] drm_dp_mst_topology: use correct AUX channel

From: "Ville Syrjälä" <ville.syrjala@linux.intel.com>
To: Sam McNally <sammc@chromium.org>
Cc: LKML <linux-kernel@vger.kernel.org>,
	Thomas Zimmermann <tzimmermann@suse.de>,
	David Airlie <airlied@linux.ie>,
	Hans Verkuil <hverkuil@xs4all.nl>,
	Hans Verkuil <hans.verkuil@cisco.com>,
	dri-devel@lists.freedesktop.org
Subject: Re: [PATCH v3 2/4] drm_dp_mst_topology: use correct AUX channel
Date: Tue, 2 Feb 2021 00:13:50 +0200	[thread overview]
Message-ID: <YBh9HvbIRF4zd+AK@intel.com> (raw)
In-Reply-To: <20200923121320.v3.2.Ided0ab0808c4908238bd2eb9ebb6ffb2c9312789@changeid>

On Wed, Sep 23, 2020 at 12:13:53PM +1000, Sam McNally wrote:
> From: Hans Verkuil <hans.verkuil@cisco.com>
> 
> For adapters behind an MST hub use the correct AUX channel.
> 
> Signed-off-by: Hans Verkuil <hans.verkuil@cisco.com>
> [sammc@chromium.org: rebased, removing redundant changes]
> Signed-off-by: Sam McNally <sammc@chromium.org>
> ---
> 
> (no changes since v1)
> 
>  drivers/gpu/drm/drm_dp_mst_topology.c | 36 +++++++++++++++++++++++++++
>  1 file changed, 36 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_dp_mst_topology.c b/drivers/gpu/drm/drm_dp_mst_topology.c
> index 15b6cc39a754..0d753201adbd 100644
> --- a/drivers/gpu/drm/drm_dp_mst_topology.c
> +++ b/drivers/gpu/drm/drm_dp_mst_topology.c
> @@ -2255,6 +2255,9 @@ drm_dp_mst_topology_unlink_port(struct drm_dp_mst_topology_mgr *mgr,
>  	drm_dp_mst_topology_put_port(port);
>  }
>  
> +static ssize_t
> +drm_dp_mst_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg);
> +
>  static struct drm_dp_mst_port *
>  drm_dp_mst_add_port(struct drm_device *dev,
>  		    struct drm_dp_mst_topology_mgr *mgr,
> @@ -2271,9 +2274,13 @@ drm_dp_mst_add_port(struct drm_device *dev,
>  	port->port_num = port_number;
>  	port->mgr = mgr;
>  	port->aux.name = "DPMST";
> +	mutex_init(&port->aux.hw_mutex);
> +	mutex_init(&port->aux.cec.lock);
>  	port->aux.dev = dev->dev;
>  	port->aux.is_remote = true;
>  
> +	port->aux.transfer = drm_dp_mst_aux_transfer;
> +

This was supposed to be handled via higher levels checking for
is_remote==true.

>  	/* initialize the MST downstream port's AUX crc work queue */
>  	drm_dp_remote_aux_init(&port->aux);
>  
> @@ -3503,6 +3510,35 @@ static int drm_dp_send_up_ack_reply(struct drm_dp_mst_topology_mgr *mgr,
>  	return 0;
>  }
>  
> +static ssize_t
> +drm_dp_mst_aux_transfer(struct drm_dp_aux *aux, struct drm_dp_aux_msg *msg)
> +{
> +	struct drm_dp_mst_port *port =
> +		container_of(aux, struct drm_dp_mst_port, aux);
> +	int ret;
> +
> +	switch (msg->request & ~DP_AUX_I2C_MOT) {
> +	case DP_AUX_NATIVE_WRITE:
> +	case DP_AUX_I2C_WRITE:
> +	case DP_AUX_I2C_WRITE_STATUS_UPDATE:
> +		ret = drm_dp_send_dpcd_write(port->mgr, port, msg->address,
> +					     msg->size, msg->buffer);

That doesn't make sense to me. I2c writes and DPCD writes
are definitely not the same thing.

aux->transfer is a very low level thing. I don't think it's the
correct level of abstraction for sideband.

> +		break;
> +
> +	case DP_AUX_NATIVE_READ:
> +	case DP_AUX_I2C_READ:
> +		ret = drm_dp_send_dpcd_read(port->mgr, port, msg->address,
> +					    msg->size, msg->buffer);
> +		break;
> +
> +	default:
> +		ret = -EINVAL;
> +		break;
> +	}
> +
> +	return ret;
> +}
> +
>  static int drm_dp_get_vc_payload_bw(u8 dp_link_bw, u8  dp_link_count)
>  {
>  	if (dp_link_bw == 0 || dp_link_count == 0)
> -- 
> 2.28.0.681.g6f77f65b4e-goog
> 
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-- 
Ville Syrjälä
Intel