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Message-ID: <f415aa0c-edf8-94de-bde8-faf151f5f530@linaro.org>
Date: Wed, 1 Jun 2022 23:46:54 +0300
From: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
To: Douglas Anderson <dianders@...omium.org>,
dri-devel@...ts.freedesktop.org
Cc: Hsin-Yi Wang <hsinyi@...omium.org>,
Abhinav Kumar <quic_abhinavk@...cinc.com>,
Philip Chen <philipchen@...omium.org>,
Sankeerth Billakanti <quic_sbillaka@...cinc.com>,
Robert Foss <robert.foss@...aro.org>,
freedreno@...ts.freedesktop.org, linux-arm-msm@...r.kernel.org,
Stephen Boyd <swboyd@...omium.org>,
Andrzej Hajda <andrzej.hajda@...el.com>,
Daniel Vetter <daniel@...ll.ch>,
David Airlie <airlied@...ux.ie>,
Jernej Skrabec <jernej.skrabec@...il.com>,
Jonas Karlman <jonas@...boo.se>,
Laurent Pinchart <Laurent.pinchart@...asonboard.com>,
Neil Armstrong <narmstrong@...libre.com>,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH v3 4/4] drm/bridge: parade-ps8640: Handle DP AUX more
properly
On 10/05/2022 22:29, Douglas Anderson wrote:
> While it works, for the most part, to assume that the panel has
> finished probing when devm_of_dp_aux_populate_ep_devices() returns,
> it's a bit fragile. This is talked about at length in commit
> a1e3667a9835 ("drm/bridge: ti-sn65dsi86: Promote the AUX channel to
> its own sub-dev").
>
> When reviewing the ps8640 code, I managed to convince myself that it
> was OK not to worry about it there and that maybe it wasn't really
> _that_ fragile. However, it turns out that it really is. Simply
> hardcoding panel_edp_probe() to return -EPROBE_DEFER was enough to put
> the boot process into an infinite loop. I believe this manages to trip
> the same issues that we used to trip with the main MSM code where
> something about our actions trigger Linux to re-probe previously
> deferred devices right away and each time we try again we re-trigger
> Linux to re-probe.
>
> Let's fix this using the callback introduced in the patch ("drm/dp:
> Callbacks to make it easier for drivers to use DP AUX bus properly").
> When using the new callback, we have to be a little careful. The
> probe_done() callback is no longer always called in the context of
> our probe routine. That means we can't rely on being able to return
> -EPROBE_DEFER from it. We re-jigger the order of things a bit to
> account for that.
>
> With this change, the device still boots (though obviously the panel
> doesn't come up) if I force panel-edp to always return
> -EPROBE_DEFER. If I fake it and make the panel probe exactly once it
> also works.
>
> Signed-off-by: Douglas Anderson <dianders@...omium.org>
Reviewed-by: Dmitry Baryshkov <dmitry.baryshkov@...aro.org>
> ---
>
> Changes in v3:
> - Adapt to v3 changes in aux bus.
> - Use devm_drm_bridge_add() to simplify.
>
> Changes in v2:
> - Rewrote atop new method introduced by patch #1.
>
> drivers/gpu/drm/bridge/parade-ps8640.c | 74 ++++++++++++++++----------
> 1 file changed, 46 insertions(+), 28 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/parade-ps8640.c b/drivers/gpu/drm/bridge/parade-ps8640.c
> index e2467e58b5b7..ff4227f6d800 100644
> --- a/drivers/gpu/drm/bridge/parade-ps8640.c
> +++ b/drivers/gpu/drm/bridge/parade-ps8640.c
> @@ -537,7 +537,7 @@ static const struct drm_bridge_funcs ps8640_bridge_funcs = {
> .pre_enable = ps8640_pre_enable,
> };
>
> -static int ps8640_bridge_host_attach(struct device *dev, struct ps8640 *ps_bridge)
> +static int ps8640_bridge_get_dsi_resources(struct device *dev, struct ps8640 *ps_bridge)
> {
> struct device_node *in_ep, *dsi_node;
> struct mipi_dsi_device *dsi;
> @@ -576,13 +576,40 @@ static int ps8640_bridge_host_attach(struct device *dev, struct ps8640 *ps_bridg
> dsi->format = MIPI_DSI_FMT_RGB888;
> dsi->lanes = NUM_MIPI_LANES;
>
> - return devm_mipi_dsi_attach(dev, dsi);
> + return 0;
> +}
> +
> +static int ps8640_bridge_link_panel(struct drm_dp_aux *aux)
> +{
> + struct ps8640 *ps_bridge = aux_to_ps8640(aux);
> + struct device *dev = aux->dev;
> + struct device_node *np = dev->of_node;
> + int ret;
> +
> + /*
> + * NOTE about returning -EPROBE_DEFER from this function: if we
> + * return an error (most relevant to -EPROBE_DEFER) it will only
> + * be passed out to ps8640_probe() if it called this directly (AKA the
> + * panel isn't under the "aux-bus" node). That should be fine because
> + * if the panel is under "aux-bus" it's guaranteed to have probed by
> + * the time this function has been called.
> + */
> +
> + /* port@1 is ps8640 output port */
> + ps_bridge->panel_bridge = devm_drm_of_get_bridge(dev, np, 1, 0);
> + if (IS_ERR(ps_bridge->panel_bridge))
> + return PTR_ERR(ps_bridge->panel_bridge);
> +
> + ret = devm_drm_bridge_add(dev, &ps_bridge->bridge);
> + if (ret)
> + return ret;
> +
> + return devm_mipi_dsi_attach(dev, ps_bridge->dsi);
> }
>
> static int ps8640_probe(struct i2c_client *client)
> {
> struct device *dev = &client->dev;
> - struct device_node *np = dev->of_node;
> struct ps8640 *ps_bridge;
> int ret;
> u32 i;
> @@ -623,6 +650,14 @@ static int ps8640_probe(struct i2c_client *client)
> if (!ps8640_of_panel_on_aux_bus(&client->dev))
> ps_bridge->bridge.ops = DRM_BRIDGE_OP_EDID;
>
> + /*
> + * Get MIPI DSI resources early. These can return -EPROBE_DEFER so
> + * we want to get them out of the way sooner.
> + */
> + ret = ps8640_bridge_get_dsi_resources(&client->dev, ps_bridge);
> + if (ret)
> + return ret;
> +
> ps_bridge->page[PAGE0_DP_CNTL] = client;
>
> ps_bridge->regmap[PAGE0_DP_CNTL] = devm_regmap_init_i2c(client, ps8640_regmap_config);
> @@ -665,35 +700,19 @@ static int ps8640_probe(struct i2c_client *client)
> if (ret)
> return ret;
>
> - devm_of_dp_aux_populate_ep_devices(&ps_bridge->aux);
> + ret = devm_of_dp_aux_populate_bus(&ps_bridge->aux, ps8640_bridge_link_panel);
>
> - /* port@1 is ps8640 output port */
> - ps_bridge->panel_bridge = devm_drm_of_get_bridge(dev, np, 1, 0);
> - if (IS_ERR(ps_bridge->panel_bridge))
> - return PTR_ERR(ps_bridge->panel_bridge);
> -
> - drm_bridge_add(&ps_bridge->bridge);
> -
> - ret = ps8640_bridge_host_attach(dev, ps_bridge);
> - if (ret)
> - goto err_bridge_remove;
> -
> - return 0;
> + /*
> + * If devm_of_dp_aux_populate_bus() returns -ENODEV then it's up to
> + * usa to call ps8640_bridge_link_panel() directly. NOTE: in this case
> + * the function is allowed to -EPROBE_DEFER.
> + */
> + if (ret == -ENODEV)
> + return ps8640_bridge_link_panel(&ps_bridge->aux);
>
> -err_bridge_remove:
> - drm_bridge_remove(&ps_bridge->bridge);
> return ret;
> }
>
> -static int ps8640_remove(struct i2c_client *client)
> -{
> - struct ps8640 *ps_bridge = i2c_get_clientdata(client);
> -
> - drm_bridge_remove(&ps_bridge->bridge);
> -
> - return 0;
> -}
> -
> static const struct of_device_id ps8640_match[] = {
> { .compatible = "parade,ps8640" },
> { }
> @@ -702,7 +721,6 @@ MODULE_DEVICE_TABLE(of, ps8640_match);
>
> static struct i2c_driver ps8640_driver = {
> .probe_new = ps8640_probe,
> - .remove = ps8640_remove,
> .driver = {
> .name = "ps8640",
> .of_match_table = ps8640_match,
--
With best wishes
Dmitry
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