Re: [PATCH] drm: call connector->dpms(OFF) when disabling

[Daniel Vetter <daniel@ffwll.ch>]

On Fri, Sep 28, 2012 at 09:27:18AM +0200, Rob Clark wrote:
> From: Rob Clark <rob@ti.com>
> 
> When disabling unused connectors, be sure to call connector->dpms(OFF),
> so if there is actually some IP to turn off (such as external bridge
> chips, etc), these actually do get turned off.
> 
> Signed-off-by: Rob Clark <rob@ti.com>
> Tested-by: Roger Quadros <rogerq@ti.com>

I think this runs counter to the crtc helper design: connectors are pretty
much just dummy entities, and any dpms handling is done in the
encoders/crtcs. If you call connector->funcs->dpms you don't call a crtc
helper function, but actually the official dpms interface (which then
again calls down into the encoder/crtc dpms callbacks (which are again
crtc helper private). This functions are called again a few lines down in
disable_unused_functions anyway, so the only way this changes behaviour is
if you already overwrite the dpms interface and don't directly use
drm_helper_connector_dpms.

Which is imo a clear sign that the crtc helper is a misfit for your hw and
you should stop using it ;-) And adding special-case handling like this
into common code, especially if it weakens the semantic concepts in the
helper layer is a recipe for a maintainance disaster a few years down the
road. Hence

NACKed-by: Daniel Vetter <daniel.vetter@ffwll.ch>

Cheers, Daniel
> 
> ---
>  drivers/gpu/drm/drm_crtc_helper.c |    6 +++---
>  1 file changed, 3 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/drm_crtc_helper.c b/drivers/gpu/drm/drm_crtc_helper.c
> index 3252e70..000cda4 100644
> --- a/drivers/gpu/drm/drm_crtc_helper.c
> +++ b/drivers/gpu/drm/drm_crtc_helper.c
> @@ -244,16 +244,16 @@ void drm_helper_disable_unused_functions(struct drm_device *dev)
>  	struct drm_crtc *crtc;
>  
>  	list_for_each_entry(connector, &dev->mode_config.connector_list, head) {
> -		if (!connector->encoder)
> -			continue;
>  		if (connector->status == connector_status_disconnected)
>  			connector->encoder = NULL;
> +		if (!connector->encoder)
> +			connector->funcs->dpms(connector, DRM_MODE_DPMS_OFF);
>  	}
>  
>  	list_for_each_entry(encoder, &dev->mode_config.encoder_list, head) {
>  		if (!drm_helper_encoder_in_use(encoder)) {
>  			drm_encoder_disable(encoder);
> -			/* disconnector encoder from any connector */
> +			/* disconnect encoder from any connector */
>  			encoder->crtc = NULL;
>  		}
>  	}
> -- 
> 1.7.9.5
> 
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> 
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-- 
Daniel Vetter
Software Engineer, Intel Corporation
+41 (0) 79 365 57 48 - http://blog.ffwll.ch