linux-kernel - Re: [PATCH v3] gpu/drm: mediatek: call mtk_dsi_stop() after mtk_drm_crtc_atomic

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Date:   Tue, 28 May 2019 16:53:06 +0800
From:   CK Hu <ck.hu@...iatek.com>
To:     Hsin-Yi Wang <hsinyi@...omium.org>
CC:     <linux-arm-kernel@...ts.infradead.org>,
        Philipp Zabel <p.zabel@...gutronix.de>,
        David Airlie <airlied@...ux.ie>,
        <linux-kernel@...r.kernel.org>, <dri-devel@...ts.freedesktop.org>,
        "Matthias Brugger" <matthias.bgg@...il.com>,
        <linux-mediatek@...ts.infradead.org>,
        Daniel Vetter <daniel@...ll.ch>
Subject: Re: [PATCH v3] gpu/drm: mediatek: call mtk_dsi_stop() after
 mtk_drm_crtc_atomic_disable()

Hi, Hsin-Yi:

On Tue, 2019-05-28 at 15:39 +0800, Hsin-Yi Wang wrote:
> mtk_dsi_stop() should be called after mtk_drm_crtc_atomic_disable(), which needs
> ovl irq for drm_crtc_wait_one_vblank(), since after mtk_dsi_stop() is called,
> ovl irq will be disabled. If drm_crtc_wait_one_vblank() is called after last
> irq, it will timeout with this message: "vblank wait timed out on crtc 0". This
> happens sometimes when turning off the screen.
> 
> In drm_atomic_helper.c#disable_outputs(),
> the calling sequence when turning off the screen is:
> 
> 1. mtk_dsi_encoder_disable()
>      --> mtk_output_dsi_disable()
>        --> mtk_dsi_stop();  // sometimes make vblank timeout in atomic_disable
>        --> mtk_dsi_poweroff();
> 2. mtk_drm_crtc_atomic_disable()
>      --> drm_crtc_wait_one_vblank();
>      ...
>        --> mtk_dsi_ddp_stop()
>          --> mtk_dsi_poweroff();
> 
> mtk_dsi_poweroff() has reference count design, change to make mtk_dsi_stop()
> called in mtk_dsi_poweroff() when refcount is 0.
> 
> Fixes: 0707632b5bac ("drm/mediatek: update DSI sub driver flow for sending commands to panel")
> Signed-off-by: Hsin-Yi Wang <hsinyi@...omium.org>
> ---
> change log v2->v3:
> * remove unnecessary codes in unbind
> * based on discussion in v2, if we move mtk_dsi_start() to mtk_dsi_poweron(),
> in order to make mtk_dsi_start() and mtk_dsi_stop() symmetric, will results in
> no irq for panel with bridge. So we keep mtk_dsi_start() in original place.

I think we've already discussed in [1]. I need a reason to understand
this is hardware behavior or software bug. If this is a software bug, we
need to fix the bug and code could be symmetric.

[1]
http://lists.infradead.org/pipermail/linux-mediatek/2019-March/018423.html

Regards,
CK

> ---
>  drivers/gpu/drm/mediatek/mtk_dsi.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/gpu/drm/mediatek/mtk_dsi.c b/drivers/gpu/drm/mediatek/mtk_dsi.c
> index b00eb2d2e086..b7f829ecd3ad 100644
> --- a/drivers/gpu/drm/mediatek/mtk_dsi.c
> +++ b/drivers/gpu/drm/mediatek/mtk_dsi.c
> @@ -630,6 +630,8 @@ static void mtk_dsi_poweroff(struct mtk_dsi *dsi)
>  	if (--dsi->refcount != 0)
>  		return;
>  
> +	mtk_dsi_stop(dsi);
> +
>  	if (!mtk_dsi_switch_to_cmd_mode(dsi, VM_DONE_INT_FLAG, 500)) {
>  		if (dsi->panel) {
>  			if (drm_panel_unprepare(dsi->panel)) {
> @@ -696,7 +698,6 @@ static void mtk_output_dsi_disable(struct mtk_dsi *dsi)
>  		}
>  	}
>  
> -	mtk_dsi_stop(dsi);
>  	mtk_dsi_poweroff(dsi);
>  
>  	dsi->enabled = false;