[PATCH] drm/fb-helper: Blacklist writeback when adding connectors to fbdev

[PATCH] drm/fb-helper: Blacklist writeback when adding connectors to fbdev

[Paul Kocialkowski]

Writeback connectors do not produce any on-screen output and require
special care for use. Such connectors are hidden from enumeration in
DRM resources by default, but they are still picked-up by fbdev.
This makes rather little sense since fbdev is not really adapted for
dealing with writeback.

Moreover, this is also a source of issues when userspace disables the
CRTC (and associated plane) without detaching the CRTC from the
connector (which is hidden by default). In this case, the connector is
still using the CRTC, leading to am "enabled/connectors mismatch" and
eventually the failure of the associated atomic commit. This situation
happens with VC4 testing under IGT GPU Tools.

Filter out writeback connectors in the fbdev helper to solve this.

Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
---
 drivers/gpu/drm/drm_fb_helper.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
index a502f3e519fd..dd852a25d375 100644
--- a/drivers/gpu/drm/drm_fb_helper.c
+++ b/drivers/gpu/drm/drm_fb_helper.c
@@ -219,6 +219,9 @@ int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper)
 	mutex_lock(&fb_helper->lock);
 	drm_connector_list_iter_begin(dev, &conn_iter);
 	drm_for_each_connector_iter(connector, &conn_iter) {
+		if (connector->connector_type == DRM_MODE_CONNECTOR_WRITEBACK)
+			continue;
+
 		ret = __drm_fb_helper_add_one_connector(fb_helper, connector);
 		if (ret)
 			goto fail;
-- 
2.19.1

Re: [PATCH] drm/fb-helper: Blacklist writeback when adding connectors to fbdev

[Boris Brezillon]

On Thu, 15 Nov 2018 17:32:48 +0100
Paul Kocialkowski <paul.kocialkowski@bootlin.com> wrote:

> Writeback connectors do not produce any on-screen output and require
> special care for use. Such connectors are hidden from enumeration in
> DRM resources by default, but they are still picked-up by fbdev.
> This makes rather little sense since fbdev is not really adapted for
> dealing with writeback.
> 
> Moreover, this is also a source of issues when userspace disables the
> CRTC (and associated plane) without detaching the CRTC from the
> connector (which is hidden by default). In this case, the connector is
> still using the CRTC, leading to am "enabled/connectors mismatch" and

				   ^an

> eventually the failure of the associated atomic commit. This situation
> happens with VC4 testing under IGT GPU Tools.
> 
> Filter out writeback connectors in the fbdev helper to solve this.
> 
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>

Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>

> ---
>  drivers/gpu/drm/drm_fb_helper.c | 3 +++
>  1 file changed, 3 insertions(+)
> 
> diff --git a/drivers/gpu/drm/drm_fb_helper.c b/drivers/gpu/drm/drm_fb_helper.c
> index a502f3e519fd..dd852a25d375 100644
> --- a/drivers/gpu/drm/drm_fb_helper.c
> +++ b/drivers/gpu/drm/drm_fb_helper.c
> @@ -219,6 +219,9 @@ int drm_fb_helper_single_add_all_connectors(struct drm_fb_helper *fb_helper)
>  	mutex_lock(&fb_helper->lock);
>  	drm_connector_list_iter_begin(dev, &conn_iter);
>  	drm_for_each_connector_iter(connector, &conn_iter) {
> +		if (connector->connector_type == DRM_MODE_CONNECTOR_WRITEBACK)
> +			continue;
> +
>  		ret = __drm_fb_helper_add_one_connector(fb_helper, connector);
>  		if (ret)
>  			goto fail;

Re: [PATCH] drm/fb-helper: Blacklist writeback when adding connectors to fbdev

[Maxime Ripard]

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On Thu, Nov 15, 2018 at 05:32:48PM +0100, Paul Kocialkowski wrote:
> Writeback connectors do not produce any on-screen output and require
> special care for use. Such connectors are hidden from enumeration in
> DRM resources by default, but they are still picked-up by fbdev.
> This makes rather little sense since fbdev is not really adapted for
> dealing with writeback.
> 
> Moreover, this is also a source of issues when userspace disables the
> CRTC (and associated plane) without detaching the CRTC from the
> connector (which is hidden by default). In this case, the connector is
> still using the CRTC, leading to am "enabled/connectors mismatch" and
> eventually the failure of the associated atomic commit. This situation
> happens with VC4 testing under IGT GPU Tools.
> 
> Filter out writeback connectors in the fbdev helper to solve this.
> 
> Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>

Reviewed-by: Maxime Ripard <maxime.ripard@bootlin.com>
Tested-by: Maxime Ripard <maxime.ripard@bootlin.com>

Thanks!
Maxime

-- 
Maxime Ripard, Bootlin
Embedded Linux and Kernel engineering
https://bootlin.com

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Re: [PATCH] drm/fb-helper: Blacklist writeback when adding connectors to fbdev

[Daniel Vetter]

On Mon, Nov 19, 2018 at 10:28:35AM +0100, Maxime Ripard wrote:
> On Thu, Nov 15, 2018 at 05:32:48PM +0100, Paul Kocialkowski wrote:
> > Writeback connectors do not produce any on-screen output and require
> > special care for use. Such connectors are hidden from enumeration in
> > DRM resources by default, but they are still picked-up by fbdev.
> > This makes rather little sense since fbdev is not really adapted for
> > dealing with writeback.
> > 
> > Moreover, this is also a source of issues when userspace disables the
> > CRTC (and associated plane) without detaching the CRTC from the
> > connector (which is hidden by default). In this case, the connector is
> > still using the CRTC, leading to am "enabled/connectors mismatch" and
> > eventually the failure of the associated atomic commit. This situation
> > happens with VC4 testing under IGT GPU Tools.
> > 
> > Filter out writeback connectors in the fbdev helper to solve this.
> > 
> > Signed-off-by: Paul Kocialkowski <paul.kocialkowski@bootlin.com>
> 
> Reviewed-by: Maxime Ripard <maxime.ripard@bootlin.com>
> Tested-by: Maxime Ripard <maxime.ripard@bootlin.com>

Applied with a cc: stable to drm-misc-fixes. Btw, 2 r-b from committers,
someone should have pushed this I think :-)

Thanks for patch&review.
-Daniel
-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch