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

Luca Ceresoli
2025-02-07T08:59:43Z

On Fri, 7 Feb 2025 04:55:54 +0200
Dmitry Baryshkov <dmitry.baryshkov@linaro.org> wrote:

> 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).

OK

> > - 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?

It can't indeed. Dropping the second condition.

>
> > + 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.

OK. With this change it doesn't make sense to have a temporary
out_bridge variable, so I'll drop it as well.

Luca

--
Luca Ceresoli, Bootlin
Embedded Linux and Kernel engineering