linux-kernel - Re: [PATCH v2 7/7] drm/mediatek: Fix mtk_atomic_complete for runtime

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Date:	Thu, 4 Aug 2016 12:42:23 +0200
From:	Daniel Vetter <daniel@...ll.ch>
To:	Bibby Hsieh <bibby.hsieh@...iatek.com>
Cc:	David Airlie <airlied@...ux.ie>,
	Matthias Brugger <matthias.bgg@...il.com>,
	Daniel Vetter <daniel.vetter@...ll.ch>,
	dri-devel@...ts.freedesktop.org,
	linux-mediatek@...ts.infradead.org,
	Yingjoe Chen <yingjoe.chen@...iatek.com>,
	Cawa Cheng <cawa.cheng@...iatek.com>,
	Daniel Kurtz <djkurtz@...omium.org>,
	Philipp Zabel <p.zabel@...gutronix.de>,
	YT Shen <yt.shen@...iatek.com>,
	Thierry Reding <thierry.reding@...il.com>,
	CK Hu <ck.hu@...iatek.com>, Mao Huang <littlecvr@...omium.org>,
	linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
	Sascha Hauer <kernel@...gutronix.de>
Subject: Re: [PATCH v2 7/7] drm/mediatek: Fix mtk_atomic_complete for
 runtime_pm

On Thu, Aug 04, 2016 at 10:59:57AM +0800, Bibby Hsieh wrote:
> To properly implement atomic w/ runtime pm, we move
> drm_atomic_helper_commit_modeset_enables() above
> drm_atomic_helper_commit_planes() to ensure CRTCs are enabled before
> modifying plane registers, and set active_only to true to filter out
> plane update notifications when the CRTC is disabled.
> 
> According to the document from linux kernel:
> Set the active_only parameters to true in order not to receive plane
> update notifications related to a disabled CRTC. This avoids the need
> to manually ignore plane updates in driver code when the driver and/or
> hardware can't or just don't need to deal with updates on disabled
> CRTCs, for example when supporting runtime PM.
> 
> Signed-off-by: Bibby Hsieh <bibby.hsieh@...iatek.com>
> Signed-off-by: Daniel Kurtz <djkurtz@...omium.org>

btw if you want to clean up some more code, would be neat to switch
mediatek to the generic nonblocking support in the atomic helpers instead
of rolling your own.
-Daniel

> ---
>  drivers/gpu/drm/mediatek/mtk_drm_drv.c |   17 ++++++++++++++++-
>  1 file changed, 16 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_drm_drv.c b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> index b1223d5..507392a 100644
> --- a/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> +++ b/drivers/gpu/drm/mediatek/mtk_drm_drv.c
> @@ -61,10 +61,25 @@ static void mtk_atomic_complete(struct mtk_drm_private *private,
>  
>  	mtk_atomic_wait_for_fences(state);
>  
> +	/*
> +	 * Mediatek drm supports runtime PM, so plane registers cannot be
> +	 * written when their crtc is disabled.
> +	 *
> +	 * The comment for drm_atomic_helper_commit states:
> +	 *     For drivers supporting runtime PM the recommended sequence is
> +	 *
> +	 *     drm_atomic_helper_commit_modeset_disables(dev, state);
> +	 *     drm_atomic_helper_commit_modeset_enables(dev, state);
> +	 *     drm_atomic_helper_commit_planes(dev, state, true);
> +	 *
> +	 * See the kerneldoc entries for these three functions for more details.
> +	 */
>  	drm_atomic_helper_commit_modeset_disables(drm, state);
> -	drm_atomic_helper_commit_planes(drm, state, false);
>  	drm_atomic_helper_commit_modeset_enables(drm, state);
> +	drm_atomic_helper_commit_planes(drm, state, true);
> +
>  	drm_atomic_helper_wait_for_vblanks(drm, state);
> +
>  	drm_atomic_helper_cleanup_planes(drm, state);
>  	drm_atomic_state_free(state);
>  }
> -- 
> 1.7.9.5
> 

-- 
Daniel Vetter
Software Engineer, Intel Corporation
http://blog.ffwll.ch