[PATCH v4 2/2] drm/panel: Add device_link from panel device to drm device

[Linus Walleij]

On Thu, Apr 26, 2018 at 10:07 AM Jyri Sarha <jsarha at ti.com> wrote:

> Add device_link from panel device (supplier) to drm device (consumer)
> when drm_panel_attach() is called. This patch should protect the
> master drm driver if an attached panel driver unbinds while it is in
> use. The device_link should make sure the drm device is unbound before
> the panel driver becomes unavailable.
>
> The device_link is removed when drm_panel_detach() is called. The
> drm_panel_detach() should be called by the consumer DRM driver, not the
> panel driver, otherwise both drivers are racing to delete the same link.
>
> Signed-off-by: Jyri Sarha <jsarha at ti.com>
> Reviewed-by: Eric Anholt <eric at anholt.net>

Hi I have a problem with an in-development driver and this patch.

Do not worry! It is no regression. I just need help to do things right
now.

My panel is a DSI device on a DSI master:

                mcde at a0350000 {
                        status = "okay";

                        dsi at a0351000 {
                                port {
                                        dsi0_out: endpoint {
                                                remote-endpoint = <&panel_in>;
                                        };
                                };

                                panel: display {
                                        compatible = "samsung,s6d16d0";
                                        reg = <0>;
                                        /* VDD1 on the component */
                                        power-supply = <&ab8500_ldo_aux1_reg>;
                                        reset-gpios = <&gpio2 1
GPIO_ACTIVE_LOW>;

                                        port {
                                                panel_in: endpoint {

remote-endpoint = <&dsi0_out>;
                                                };
                                        };
                                };
                        };
                };

So in my DSI host driver .bind() I do:

    drm_encoder_init(drm, encoder, &mcde_dsi_encoder_funcs,
             DRM_MODE_ENCODER_DSI, NULL);
    drm_encoder_helper_add(encoder, &mcde_dsi_encoder_helper_funcs);
    ret = drm_connector_init(encoder->dev, connector,
                 &mcde_dsi_connector_funcs,
                 DRM_MODE_CONNECTOR_DSI);

    drm_connector_helper_add(connector, &mcde_dsi_connector_helper_funcs);
    drm_connector_attach_encoder(connector, encoder);
    drm_connector_register(connector);

This works fine. I managed to create the encoder and connector for this
DSI. Then:

    ret = drm_of_find_panel_or_bridge(dev->of_node,
                      0, 0, &panel, &bridge);
    if (panel) {
        bridge = drm_panel_bridge_add(panel,
                          DRM_MODE_CONNECTOR_DSI);
        if (IS_ERR(bridge)) {
            dev_err(dev, "error adding panel bridge\n");
            return PTR_ERR(bridge);
        }
        dev_info(dev, "connected to panel\n");
        d->panel = panel;
    }
    d->connector.status = connector_status_connected;
    ret = drm_bridge_attach(encoder, bridge, NULL);

And this is where it blows up: it fails in
device_link_add(connector->dev->dev, panel->dev, 0);
device_is_dependent(consumer, supplier) because the
consumer (connector) is dependent on the supplier (bridge).

This happens because the connector struct device is the
same as the bridge struct device, I suppose.

Isn't that OK? Please help me to see what's wrong with
my architecture here, and what I need to do :/ I tried to
follow examples set by MSM and Exynos DSI.

Yours,
Linus Walleij