Re: [PATCH v4 25/27] drm/bridge: ti-sn65dsi86: Don't read EDID blob over DDC

Bjorn Andersson
2021-04-23T16:13:49Z

On Fri 16 Apr 17:39 CDT 2021, Douglas Anderson wrote:

> This is really just a revert of commit 58074b08c04a ("drm/bridge:
> ti-sn65dsi86: Read EDID blob over DDC"), resolving conflicts.
>
> The old code failed to read the EDID properly in a very important
> case: before the bridge's pre_enable() was called. The way things need
> to work:
> 1. Read the EDID.
> 2. Based on the EDID, decide on video settings and pixel clock.
> 3. Enable the bridge w/ the desired settings.
>
> The way things were working:
> 1. Try to read the EDID but fail; fall back to hardcoded values.
> 2. Based on hardcoded values, decide on video settings and pixel clock.
> 3. Enable the bridge w/ the desired settings.
> 4. Try again to read the EDID, it works now!
> 5. Realize that the hardcoded settings weren't quite right.
> 6. Disable / reenable the bridge w/ the right settings.
>
> The reasons for the failures were twofold:
> a) Since we never ran the bridge chip's pre-enable then we never set
> the bit to ignore HPD. This meant the bridge chip didn't even _try_
> to go out on the bus and communicate with the panel.
> b) Even if we fixed things to ignore HPD, the EDID still wouldn't read
> if the panel wasn't on.
>
> Instead of reverting the code, we could fix it to set the HPD bit and
> also power on the panel. However, it also works nicely to just let the
> panel code read the EDID. Now that we've split the driver up we can
> expose the DDC AUX channel bus to the panel node. The panel can take
> charge of reading the EDID.
>
> NOTE: in order for things to work, anyone that needs to read the EDID
> will need to add something that looks like this to their panel in the
> dts:
> ddc-i2c-bus = <&sn65dsi86_bridge>;
>
> Presumably it's OK to land this without waiting for users to add the
> dts property since the EDID reading was a bit broken anyway, was
> "recently" added, and we know we must have the fallback mode to use
> (since the EDID reading was a bit broken).
>
> Suggested-by: Andrzej Hajda <a.hajda@samsung.com>
> Signed-off-by: Douglas Anderson <dianders@chromium.org>

Reviewed-by: Bjorn Andersson <bjorn.andersson@linaro.org>

Regards,
Bjorn

> ---
>
> (no changes since v1)
>
> drivers/gpu/drm/bridge/ti-sn65dsi86.c | 22 ----------------------
> 1 file changed, 22 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/ti-sn65dsi86.c b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> index 8253098bcdbf..62904dfdee0a 100644
> --- a/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> +++ b/drivers/gpu/drm/bridge/ti-sn65dsi86.c
> @@ -125,7 +125,6 @@
> * @connector: Our connector.
> * @host_node: Remote DSI node.
> * @dsi: Our MIPI DSI source.
> - * @edid: Detected EDID of eDP panel.
> * @refclk: Our reference clock.
> * @panel: Our panel.
> * @enable_gpio: The GPIO we toggle to enable the bridge.
> @@ -156,7 +155,6 @@ struct ti_sn65dsi86 {
> struct drm_dp_aux aux;
> struct drm_bridge bridge;
> struct drm_connector connector;
> - struct edid *edid;
> struct device_node *host_node;
> struct mipi_dsi_device *dsi;
> struct clk *refclk;
> @@ -404,24 +402,6 @@ connector_to_ti_sn65dsi86(struct drm_connector *connector)
> static int ti_sn_bridge_connector_get_modes(struct drm_connector *connector)
> {
> struct ti_sn65dsi86 *pdata = connector_to_ti_sn65dsi86(connector);
> - struct edid *edid = pdata->edid;
> - int num, ret;
> -
> - if (!edid) {
> - pm_runtime_get_sync(pdata->dev);
> - edid = pdata->edid = drm_get_edid(connector, &pdata->aux.ddc);
> - pm_runtime_put_autosuspend(pdata->dev);
> - }
> -
> - if (edid && drm_edid_is_valid(edid)) {
> - ret = drm_connector_update_edid_property(connector, edid);
> - if (!ret) {
> - num = drm_add_edid_modes(connector, edid);
> - if (num)
> - return num;
> - }
> - }
> -
> return drm_panel_get_modes(pdata->panel, connector);
> }
>
> @@ -1330,8 +1310,6 @@ static void ti_sn_bridge_remove(struct auxiliary_device *adev)
> mipi_dsi_device_unregister(pdata->dsi);
> }
>
> - kfree(pdata->edid);
> -
> drm_bridge_remove(&pdata->bridge);
>
> of_node_put(pdata->host_node);
> --
> 2.31.1.368.gbe11c130af-goog
>