[PATCH] video: hdmi: request underscan by default (original) (raw)

Ville Syrjälä ville.syrjala at linux.intel.com
Tue Feb 25 02:33:21 PST 2014

On Mon, Feb 24, 2014 at 04:20:04PM -0600, Daniel Drake wrote:

Working with HDMI TVs is a real pain as they tend to overscan by default, meaning that the pixels around the edge of the framebuffer are not displayed. This is well explained here: http://mjg59.dreamwidth.org/8705.html

There is a bit in the HDMI info frame that can request that the remote display shows the full pixel data ("underscan"). For the remote display, the HDMI spec states that this is optional - it doesn't have to listen. That means that most TVs will probably ignore this. But, maybe there are a handful of TVs for which this would help the situation. As we live in a digital world, ask the remote display not to overscan by default. Signed-off-by: Daniel Drake <drake at endlessm.com>

Yeah, underscan would seem the saner default value. CEA-861 says that the source should always set the S bits appropriately if it knows what to put there, even if the sink claims that it won't respect those bits. So we're not violating the spec by doing this.

I'm thinking we should also add a connector property to allow userspace to choose the scan behaviour. Or perhaps some driver already has such a property?

I'm not sure we want to put this into hdmi.c though. Maybe better to avoid such policy in the infoframe code itself, and instead stick this into drm_hdmi_avi_infoframe_from_display_mode()?

--- drivers/video/hdmi.c | 1 + 1 file changed, 1 insertion(+)

diff --git a/drivers/video/hdmi.c b/drivers/video/hdmi.c index 9e758a8..6c2d924 100644 --- a/drivers/video/hdmi.c +++ b/drivers/video/hdmi.c @@ -54,6 +54,7 @@ int hdmiaviinfoframeinit(struct hdmiaviinfoframe *frame) frame->type = HDMIINFOFRAMETYPEAVI; frame->version = 2; frame->length = HDMIAVIINFOFRAMESIZE; + frame->scanmode = HDMISCANMODEUNDERSCAN; return 0; } -- 1.8.3.2

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-- Ville Syrjälä Intel OTC

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