drm/vc4: Skip ULPS latching when we're in that ULPS state already.

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@anholt.net>
Link: https://patchwork.freedesktop.org/patch/msgid/20171031193258.17373-1-eric@anholt.net
Reviewed-by: Boris Brezillon <boris.brezillon@bootlin.com>

diff --git a/drivers/gpu/drm/vc4/vc4_dsi.c b/drivers/gpu/drm/vc4/vc4_dsi.c
index 94085f8bcd68cb342f6e29990a41721773bb76d8..8aa8978351185209b2c76d147468ce6e18eb8155 100644 (file)
--- 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);