[PATCH] drm/mcde: Fix stability issue

[Sam Ravnborg]

Hi Linus.

On Sun, Jul 19, 2020 at 01:33:22AM +0200, Linus Walleij wrote:
> Whenener a display update was sent, apart from updating
s/Whenener/Whenever
> the memory base address we called mcde_display_send_one_frame()
                         ^ insert comma?

> which also sent a command to the display requesting the TE IRQ
> and enabling the FIFO.
> 
> When continous updates are running this is wrong: we need
> to only send this to start the flow to the display on
> the very first update. This lead to the display pipeline
> locking up and crashing.
> 
> Check if the flow is already running and in that case
> do not call mcde_display_send_one_frame().
> 
> This fixes crashes on the Samsung GT-S7710 (Skomer).
> 
> Cc: Stephan Gerhold <stephan at gerhold.net>
> Cc: stable at vger.kernel.org
> Signed-off-by: Linus Walleij <linus.walleij at linaro.org>
Patch looks fine.
Acked-by: Sam Ravnborg <sam at ravnborg.org>

> ---
>  drivers/gpu/drm/mcde/mcde_display.c | 11 ++++++++---
>  1 file changed, 8 insertions(+), 3 deletions(-)
> 
> diff --git a/drivers/gpu/drm/mcde/mcde_display.c b/drivers/gpu/drm/mcde/mcde_display.c
> index 212aee60cf61..1d8ea8830a17 100644
> --- a/drivers/gpu/drm/mcde/mcde_display.c
> +++ b/drivers/gpu/drm/mcde/mcde_display.c
> @@ -1086,9 +1086,14 @@ static void mcde_display_update(struct drm_simple_display_pipe *pipe,
>  	 */
>  	if (fb) {
>  		mcde_set_extsrc(mcde, drm_fb_cma_get_gem_addr(fb, pstate, 0));
> -		if (!mcde->video_mode)
> -			/* Send a single frame using software sync */
> -			mcde_display_send_one_frame(mcde);
> +		if (!mcde->video_mode) {
> +			/*
> +			 * Send a single frame using software sync if the flow
> +			 * is not active yet.
> +			 */
> +			if (mcde->flow_active == 0)
> +				mcde_display_send_one_frame(mcde);
> +		}
>  		dev_info_once(mcde->dev, "sent first display update\n");
>  	} else {
>  		/*
> -- 
> 2.26.2
> 
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