On Tue, Oct 11, 2016 at 6:25 PM, Ville Syrjälä <ville.syrjala@xxxxxxxxxxxxxxx> wrote: >> Writeback connector usage: >> -------------------------- >> Due to connector routing changes being treated as "full modeset" >> operations, any client which wishes to use a writeback connector >> should include the connector in every modeset. The writeback will not >> actually become active until a framebuffer is attached. >> >> The writeback itself is enabled by attaching a framebuffer to the >> FB_ID property of the connector. The driver must then ensure that the >> CRTC content of that atomic commit is written into the framebuffer. >> >> The writeback works in a one-shot mode with each atomic commit. This >> prevents the same content from being written multiple times. >> In some cases (front-buffer rendering) there might be a desire for >> continuous operation - I think a property could be added later for >> this kind of control. > > I though people agreed that this sort of thing would go through v4l. > Continously writing to the same buffer isn't perhaps all that sensible > anyway, and so we'd need queueing, which is what v4l has already. Well, > I guess we might add some queueing to atomic eventually? > > I guess for front buffer rendering type of thing you might have some > use for a continuous mode targeting a single fb. Though I think > peridically triggering a new write could do as well. Of course either > way would likely tear horribly, and having multiple buffers seems like > the better option Yeah, momentarily entirely forgot about v4l. I think making FB_ID one-shot (perhaps better to call it WRITEBACK_FB_ID to avoid confusion) is the right thing to do, and then push everything continuous to some form of drm/v4l integration. -Daniel -- Daniel Vetter Software Engineer, Intel Corporation +41 (0) 79 365 57 48 - http://blog.ffwll.ch -- To unsubscribe from this list: send the line "unsubscribe linux-media" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
