[PATCH] Revert "drm/panel: Add device_link from panel device to DRM device"

[Andrzej Hajda]

On 27.09.2018 15:50, Sean Paul wrote:
> [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?

As I wrote in original patch thread, the original patch breaks platforms
with exynos-dsi encoder.
Quite detailed explanation in the original thread [1], 1st response to
the patch.
Apparently my response was ignored :)

[1]: https://patchwork.freedesktop.org/patch/218878/

Regards
Andrzej

>
> 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 at ti.com>
>> Cc: Eric Anholt <eric at anholt.net>
>> Cc: Andrzej Hajda <a.hajda at samsung.com>
>> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
>> ---
>>  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
>>
>> _______________________________________________
>> dri-devel mailing list
>> dri-devel at lists.freedesktop.org
>> https://lists.freedesktop.org/mailman/listinfo/dri-devel