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

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Message-ID: <CAJqEsoCOJmS5aVb5du09tXUi7UUKVBQDPe5KTdcBiDr8A7kSYA@mail.gmail.com>
Date:   Fri, 5 Feb 2021 16:17:51 +1100
From:   Sam McNally <sammc@...omium.org>
To:     Hans Verkuil <hverkuil@...all.nl>
Cc:     Ville Syrjälä <ville.syrjala@...ux.intel.com>,
        LKML <linux-kernel@...r.kernel.org>,
        Thomas Zimmermann <tzimmermann@...e.de>,
        David Airlie <airlied@...ux.ie>,
        Hans Verkuil <hans.verkuil@...co.com>,
        dri-devel@...ts.freedesktop.org
Subject: Re: [PATCH v3 2/4] drm_dp_mst_topology: use correct AUX channel

On Thu, 4 Feb 2021 at 21:19, Hans Verkuil <hverkuil@...all.nl> wrote:
>
> On 01/02/2021 23:13, Ville Syrjälä wrote:
> > On Wed, Sep 23, 2020 at 12:13:53PM +1000, Sam McNally wrote:
> >> From: Hans Verkuil <hans.verkuil@...co.com>
> >>
> >> For adapters behind an MST hub use the correct AUX channel.
> >>
> >> Signed-off-by: Hans Verkuil <hans.verkuil@...co.com>
> >> [sammc@...omium.org: rebased, removing redundant changes]
> >> Signed-off-by: Sam McNally <sammc@...omium.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.
>
> Ah, I suspect this patch can be dropped entirely: it predates commit 2f221a5efed4
> ("drm/dp_mst: Add MST support to DP DPCD R/W functions").
>
> It looks like that commit basically solved what this older patch attempts to do
> as well.
>
> Sam, can you test if it works without this patch?

It almost just works; drm_dp_cec uses whether aux.transfer is non-null
to filter out non-DP connectors. Using aux.is_remote as another signal
indicating a DP connector seems plausible. We can drop this patch.
Thanks all!
>
> Regards,
>
>         Hans
>
> >
> >>      /* 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
> >>
> >> _______________________________________________
> >> dri-devel mailing list
> >> dri-devel@...ts.freedesktop.org
> >> https://lists.freedesktop.org/mailman/listinfo/dri-devel
> >
>

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