linux-kernel - Re: [PATCH] drm: sun4i: hdmi: Remove extra HPD polling

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Date:   Tue, 30 Jun 2020 10:02:37 +0200
From:   Maxime Ripard <maxime@...no.tech>
To:     Chen-Yu Tsai <wens@...nel.org>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        Chen-Yu Tsai <wens@...e.org>, dri-devel@...ts.freedesktop.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm: sun4i: hdmi: Remove extra HPD polling

Hi,

On Mon, Jun 29, 2020 at 02:00:32PM +0800, Chen-Yu Tsai wrote:
> From: Chen-Yu Tsai <wens@...e.org>
> 
> The HPD sense mechanism in Allwinner's old HDMI encoder hardware is more
> or less an input-only GPIO. Other GPIO-based HPD implementations
> directly return the current state, instead of polling for a specific
> state and returning the other if that times out.
> 
> Remove the I/O polling from sun4i_hdmi_connector_detect() and directly
> return a known state based on the current reading. This also gets rid
> of excessive CPU usage by kworker as reported on Stack Exchange [1] and
> Armbian forums [2].
> 
>  [1] https://superuser.com/questions/1515001/debian-10-buster-on-cubietruck-with-bug-in-sun4i-drm-hdmi
>  [2] https://forum.armbian.com/topic/14282-headless-systems-and-sun4i_drm_hdmi-a10a20/
> 
> Fixes: 9c5681011a0c ("drm/sun4i: Add HDMI support")
> Signed-off-by: Chen-Yu Tsai <wens@...e.org>

Applied, thanks for figuring that out

Maxime

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