On Tue, Aug 28, 2018 at 07:49:28PM +0200, Peter Rosin wrote:
On 2018-07-06 14:43, Russell King - ARM Linux wrote:
On Fri, Jul 06, 2018 at 11:03:46AM +0100, Russell King - ARM Linux wrote:
On Wed, Apr 25, 2018 at 11:01:15PM +0300, Jyri Sarha wrote:
Oh yes. But in this case the substandard solution is already there and it is already widely used, despite it being severely broken. I am merely trying to fix the existing substandard solution.
I admit that a full integration with component helpers would probably be more elegant solution to the problem, but the amount of work is just too much. The change would impact the way all the master drm drivers pull them selves together. The drivers that already use the component helpers for some internal stuff will add their own challenge. Separate component matching implementations are needed for device-tree and ACPI (are ther more flavors?) etc. I just do not see this happening any time soon (am happy to be wrong about this).
The issue is actually worse than that:
- drivers that are already componentised can't use bridges
- drivers that use bridges can't use componentised stuff
because bridges don't register themselves with the component helper, and the helpers in drm_of.c assume that all graph nodes will be components.
The whole thing about whether stuff is componentised or bridge based is really getting out of hand, and the push is towards bridge based stuff even though that is technically inferior when it comes to being able to develop and test (which involves being able to remove and re-insert modules.)
Consequently more and more code is being written for bridges, and the component helper ignored, and the problems with bridges are being ignored. This is not healthy.
The problem is only going to get worse. Someone needs to bite the bullet and fix bridges before the problem gets any more out of hand.
This patch (which is actually two patches locally) allows the component helper to know what's going on inside the bridge code wrt bridge availability, and takes the appropriate action at the correct time. No need for device links or similar, or incompatibilities between bridges and components. The only requirement is that bridges set the "device" member of struct drm_bridge to opt-in to this.
Tested with Armada converted to support bridges, TDA998x as a componentised bridge, and dumb-vga-dac as a non-componentised bridge:
root@cubox:~# less /sys/kernel/debug/device_component/display-subsystem master name status
display-subsystem bound
device name status
port registered port registered hdmi-encoder registered vga-bridge registered root@cubox:~# dmesg |grep bound [ 1.921798] armada-drm display-subsystem: bound f1820000.lcd-controller (ops armada_lcd_ops) [ 1.931014] armada-drm display-subsystem: bound f1810000.lcd-controller (ops armada_lcd_ops) [ 2.069231] armada-drm display-subsystem: bound 1-0070 (ops tda998x_ops) [ 2.076059] armada-drm display-subsystem: bound vga-bridge (ops dummy_ops)
Without this, the same DT fails because "vga-bridge" is never added to the component helpers.
What did you need to do to convert Armada to support bridges? How much work is it to convert drivers that support bridges so that they support components? Maybe that's not needed? What happens with tda998x? I mean, it already calls component_add, and with this there's an indirect call in drm_bridge_add which it also calls. I guess I'm asking if a component may call component_add several times without things sliding sideways?
The difference with tda998x is that with the code below (as it stood in an earlier revision of the bridge code, when we had a separate bridge->of_node member), bridge->device is not set for the tda998x, which avoids the duplicated component_add() - which would be illegal (and cause problems.)
However, I also hacked tda998x to make tda998x_bind() a no-op - without such a hack, the DRM driver needs to know whether the bridge is tda998x or not, so it knows whether it needs to create the encoder.
I don't think there's any simple, non-hacky solution to this problem.
diff --git a/drivers/base/component.c b/drivers/base/component.c index 8946dfee4768..b14b3a3655ea 100644 --- a/drivers/base/component.c +++ b/drivers/base/component.c @@ -602,4 +602,32 @@ void component_del(struct device *dev, const struct component_ops *ops) } EXPORT_SYMBOL_GPL(component_del);
+static int component_dummy_bind(struct device *comp, struct device *master,
void *master_data)+{
- return 0;
+}
+static void component_dummy_unbind(struct device *comp, struct device *master,
void *master_data)+{ +}
+static const struct component_ops dummy_ops = {
- .bind = component_dummy_bind,
- .unbind = component_dummy_unbind,
+};
+int component_mark_available(struct device *dev) +{
- return component_add(dev, &dummy_ops);
+} +EXPORT_SYMBOL_GPL(component_mark_available);
+void component_mark_unavailable(struct device *dev) +{
- component_del(dev, &dummy_ops);
+} +EXPORT_SYMBOL_GPL(component_mark_unavailable);
Is this really needed in component.c? I'd say that these dummy bridge_component_bind/unbind can be added directly in drm_bridge.c and that the new call to component_mark_available in drm_bridge could simply be component_add(bridge->device, &bridge_component_ops) (etc)
What if other subsystems want this functionality? IMHO, it belongs in the component layer, not in other subsystems where it could end up being duplicated.
MODULE_LICENSE("GPL v2"); diff --git a/drivers/gpu/drm/drm_bridge.c b/drivers/gpu/drm/drm_bridge.c index 1638bfe9627c..ce3ccd327916 100644 --- a/drivers/gpu/drm/drm_bridge.c +++ b/drivers/gpu/drm/drm_bridge.c @@ -21,6 +21,7 @@
- DEALINGS IN THE SOFTWARE.
*/
+#include <linux/component.h> #include <linux/err.h> #include <linux/module.h> #include <linux/mutex.h> @@ -73,6 +74,9 @@ void drm_bridge_add(struct drm_bridge *bridge) mutex_lock(&bridge_lock); list_add_tail(&bridge->list, &bridge_list); mutex_unlock(&bridge_lock);
- if (bridge->device)
WARN_ON(component_mark_available(bridge->device));} EXPORT_SYMBOL(drm_bridge_add);
@@ -83,6 +87,9 @@ EXPORT_SYMBOL(drm_bridge_add); */ void drm_bridge_remove(struct drm_bridge *bridge) {
- if (bridge->device)
component_mark_unavailable(bridge->device);- mutex_lock(&bridge_lock); list_del_init(&bridge->list); mutex_unlock(&bridge_lock);
diff --git a/include/drm/drm_bridge.h b/include/drm/drm_bridge.h index 3270fec46979..e863da14d4d9 100644 --- a/include/drm/drm_bridge.h +++ b/include/drm/drm_bridge.h @@ -268,6 +268,7 @@ struct drm_bridge { struct drm_device *dev; struct drm_encoder *encoder; struct drm_bridge *next;
- struct device *device;
In patch [1] i add struct device *odev (for owner device) and the series then proceeds to convert all bridges to add a link to its owner device and to then remove the (below) of_node member.
[1] https://lkml.org/lkml/2018/5/16/382
Would it be bad if all bridges opted in to this? In other words, could my "odev" and your "device" be shared?
No (see my explanation above about duplicate registrations not being permitted.)