[actually Cc Eric and Andrzej]
On Thu, Sep 27, 2018 at 02:41:30PM +0200, Linus Walleij wrote:
> This reverts commit 0c08754b59da5557532d946599854e6df28edc22.
>
> commit 0c08754b59da
> ("drm/panel: Add device_link from panel device to DRM device")
> creates a circular dependency under these circumstances:
>
> 1. The panel depends on dsi-host because it is MIPI-DSI child
> device.
> 2. dsi-host depends on the drm parent device (connector->dev->dev)
> this should be allowed.
> 3. drm parent dev (connector->dev->dev) depends on the panel
> after this patch.
>
> This makes the dependency circular and while it appears it
> does not affect any in-tree drivers (they do not seem to have
> dsi hosts depending on the same parent device) this does not
> seem right.
Hey Linus,
I'm trying to wrap my head around this :-)
I just read through the original patch thread. It doesn't seem like this was
introduced to fix a bug? Will reverting this cause regressions on in-tree
drivers?
What's different in your in-development driver that's causing you to hit
this?
Thanks!
Sean
>
> As noted in a response from Andrzej Hajda, the intent is
> likely to make the panel dependent on the DRM device
> (connector->dev) not its parent. But we have no way of
> doing that since the DRM device doesn't contain any
> struct device on its own (arguably it should).
>
> Revert this until a proper approach is figured out.
>
> Cc: Jyri Sarha <jsarha@xxxxxx>
> Cc: Eric Anholt <eric@xxxxxxxxxx>
> Cc: Andrzej Hajda <a.hajda@xxxxxxxxxxx>
> Signed-off-by: Linus Walleij <linus.walleij@xxxxxxxxxx>
> ---
> drivers/gpu/drm/drm_panel.c | 10 ----------
> include/drm/drm_panel.h | 1 -
> 2 files changed, 11 deletions(-)
>
> diff --git a/drivers/gpu/drm/drm_panel.c b/drivers/gpu/drm/drm_panel.c
> index b902361dee6e..1d9a9d2fe0e0 100644
> --- a/drivers/gpu/drm/drm_panel.c
> +++ b/drivers/gpu/drm/drm_panel.c
> @@ -24,7 +24,6 @@
> #include <linux/err.h>
> #include <linux/module.h>
>
> -#include <drm/drm_device.h>
> #include <drm/drm_crtc.h>
> #include <drm/drm_panel.h>
>
> @@ -105,13 +104,6 @@ int drm_panel_attach(struct drm_panel *panel, struct drm_connector *connector)
> if (panel->connector)
> return -EBUSY;
>
> - panel->link = device_link_add(connector->dev->dev, panel->dev, 0);
> - if (!panel->link) {
> - dev_err(panel->dev, "failed to link panel to %s\n",
> - dev_name(connector->dev->dev));
> - return -EINVAL;
> - }
> -
> panel->connector = connector;
> panel->drm = connector->dev;
>
> @@ -133,8 +125,6 @@ EXPORT_SYMBOL(drm_panel_attach);
> */
> int drm_panel_detach(struct drm_panel *panel)
> {
> - device_link_del(panel->link);
> -
> panel->connector = NULL;
> panel->drm = NULL;
>
> diff --git a/include/drm/drm_panel.h b/include/drm/drm_panel.h
> index 582a0ec0aa70..777814755fa6 100644
> --- a/include/drm/drm_panel.h
> +++ b/include/drm/drm_panel.h
> @@ -89,7 +89,6 @@ struct drm_panel {
> struct drm_device *drm;
> struct drm_connector *connector;
> struct device *dev;
> - struct device_link *link;
>
> const struct drm_panel_funcs *funcs;
>
> --
> 2.17.1
>
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--
Sean Paul, Software Engineer, Google / Chromium OS
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