Re: [PATCH v6 11/26] drm/bridge: samsung-dsim: use devm_drm_of_get_bridge[_by_node] to find the out_bridge

Dmitry Baryshkov
2025-02-07T02:55:59Z

On Thu, Feb 06, 2025 at 07:14:26PM +0100, Luca Ceresoli wrote:
> In order to support panels described either via graph links or via a
> subnode (e.g. "panel@0"), this driver uses low-level deprecated functions
> to find the next bridge. The resulting logic is complex and duplicates code
> already present in the DRM bridge core. Switch to the new APIs in DRM
> bridge core that allow to do the same in a much cleaner way.
>
> Note there are two slight changes in the new logic intended to improve the
> final result:
>
> * the old code looks for a subnode with any name except "port" or "ports",
> while the new code uses the node passed as a parameter
>
> * the old code looks for a subnode first and falls back to a graph link,
> while the new code uses the reverse order because graph links are the
> recommended device tree representation now
>
> The first change makes the code more robust by avoiding the risk of using
> an unrelated node which is not describing a panel and not names "port" or
> "ports".
>
> The second change is not expected to expose regressions because, in the
> cases where both a subnode and a graph link are used to describe a panel,
> the graph link should point to the subnode itself, such as in
> arch/arm64/boot/dts/qcom/sdm850-lenovo-yoga-c630.dts
>
> As a further cleanup, use a temporary variable to assign dsi->out_bridge
> only on success. This avoids the risk of leaving a non-NULL value in
> dsi->out_bridge when samsung_dsim_host_attach() fails.
>
> Suggested-by: Dmitry Baryshkov <dmitry.baryshkov@linaro.org>
> Signed-off-by: Luca Ceresoli <luca.ceresoli@bootlin.com>
>
> ---
>
> This patch was added in v6.
> ---
> drivers/gpu/drm/bridge/samsung-dsim.c | 55 ++++++-----------------------------
> 1 file changed, 9 insertions(+), 46 deletions(-)
>
> diff --git a/drivers/gpu/drm/bridge/samsung-dsim.c b/drivers/gpu/drm/bridge/samsung-dsim.c
> index f8b4fb8357659018ec0db65374ee5d05330639ae..bbd0a4f5a3f52b61bf48f10d6e8ca741bffa5e46 100644
> --- a/drivers/gpu/drm/bridge/samsung-dsim.c
> +++ b/drivers/gpu/drm/bridge/samsung-dsim.c
> @@ -1704,55 +1704,16 @@ static int samsung_dsim_host_attach(struct mipi_dsi_host *host,
> const struct samsung_dsim_plat_data *pdata = dsi->plat_data;
> struct device *dev = dsi->dev;
> struct device_node *np = dev->of_node;
> - struct device_node *remote;
> - struct drm_panel *panel;
> + struct drm_bridge *out_bridge;
> int ret;
>
> - /*
> - * Devices can also be child nodes when we also control that device
> - * through the upstream device (ie, MIPI-DCS for a MIPI-DSI device).
> - *
> - * Lookup for a child node of the given parent that isn't either port
> - * or ports.
> - */

Please leave the comment in place (maybe rewrite it slightly).

> - for_each_available_child_of_node(np, remote) {
> - if (of_node_name_eq(remote, "port") ||
> - of_node_name_eq(remote, "ports"))
> - continue;
> + out_bridge = devm_drm_of_get_bridge(dev, np, 1, 0);
> + if (IS_ERR(out_bridge) && PTR_ERR(out_bridge) != -EPROBE_DEFER)

Can it actually return EPROBE_DEFER?

> + out_bridge = devm_drm_of_get_bridge_by_node(dev, device->dev.of_node);
>
> - goto of_find_panel_or_bridge;
> - }
> -
> - /*
> - * of_graph_get_remote_node() produces a noisy error message if port
> - * node isn't found and the absence of the port is a legit case here,
> - * so at first we silently check whether graph presents in the
> - * device-tree node.
> - */
> - if (!of_graph_is_present(np))
> - return -ENODEV;
> -
> - remote = of_graph_get_remote_node(np, 1, 0);
> -
> -of_find_panel_or_bridge:
> - if (!remote)
> - return -ENODEV;
> -
> - panel = of_drm_find_panel(remote);
> - if (!IS_ERR(panel)) {
> - dsi->out_bridge = devm_drm_panel_bridge_add(dev, panel);
> - } else {
> - dsi->out_bridge = of_drm_find_bridge(remote);
> - if (!dsi->out_bridge)
> - dsi->out_bridge = ERR_PTR(-EINVAL);
> - }
> -
> - of_node_put(remote);
> -
> - if (IS_ERR(dsi->out_bridge)) {
> - ret = PTR_ERR(dsi->out_bridge);
> - DRM_DEV_ERROR(dev, "failed to find the bridge: %d\n", ret);
> - return ret;
> + if (IS_ERR(out_bridge)) {
> + DRM_DEV_ERROR(dev, "failed to find the bridge: %ld\n", PTR_ERR(out_bridge));
> + return PTR_ERR(out_bridge);
> }
>
> DRM_DEV_INFO(dev, "Attached %s device (lanes:%d bpp:%d mode-flags:0x%lx)\n",
> @@ -1784,6 +1745,8 @@ static int samsung_dsim_host_attach(struct mipi_dsi_host *host,
> dsi->format = device->format;
> dsi->mode_flags = device->mode_flags;
>
> + dsi->out_bridge = out_bridge;
> +

Please move the assignment closer to the original place.

> return 0;
> }
>
>
> --
> 2.34.1
>

--
With best wishes
Dmitry