linux-kernel - Re: [PATCH 1/2] drm/vc4: Skip ULPS latching when we're in that ULPS state already.

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Date:   Mon, 30 Apr 2018 11:03:39 +0200
From:   Boris Brezillon <boris.brezillon@...tlin.com>
To:     Eric Anholt <eric@...olt.net>
Cc:     dri-devel@...ts.freedesktop.org,
        Thierry Reding <thierry.reding@...il.com>,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH 1/2] drm/vc4: Skip ULPS latching when we're in that ULPS
 state already.

On Tue, 31 Oct 2017 12:32:57 -0700
Eric Anholt <eric@...olt.net> wrote:

> It seems that trying to go from unlatched to unlatched will time out
> waiting for STOP, and we can just skip that.
> 
> Signed-off-by: Eric Anholt <eric@...olt.net>

Reviewed-by: Boris Brezillon <boris.brezillon@...tlin.com>

> ---
>  drivers/gpu/drm/vc4/vc4_dsi.c | 5 +++++
>  1 file changed, 5 insertions(+)
> 
> diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
> index 94085f8bcd68..8aa897835118 100644
> --- a/drivers/gpu/drm/vc4/vc4_dsi.c
> +++ b/drivers/gpu/drm/vc4/vc4_dsi.c
> @@ -753,6 +753,11 @@ static void vc4_dsi_ulps(struct vc4_dsi *dsi, bool ulps)
>  			 (dsi->lanes > 2 ? DSI1_STAT_PHY_D2_STOP : 0) |
>  			 (dsi->lanes > 3 ? DSI1_STAT_PHY_D3_STOP : 0));
>  	int ret;
> +	bool ulps_currently_enabled = (DSI_PORT_READ(PHY_AFEC0) &
> +				       DSI_PORT_BIT(PHY_AFEC0_LATCH_ULPS));
> +
> +	if (ulps == ulps_currently_enabled)
> +		return;
>  
>  	DSI_PORT_WRITE(STAT, stat_ulps);
>  	DSI_PORT_WRITE(PHYC, DSI_PORT_READ(PHYC) | phyc_ulps);



-- 
Boris Brezillon, Bootlin (formerly Free Electrons)
Embedded Linux and Kernel engineering
https://bootlin.com