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Subject[PATCH v2 2/8] drm/pl111: simplify bridge timing support
Date
Simplify bridge timing support by only supporting pixel clock
polarity. This aligns pixel clock polarity handling for bridges
with displays.

Signed-off-by: Stefan Agner <stefan@agner.ch>
---
drivers/gpu/drm/pl111/pl111_display.c | 22 ++++++----------------
1 file changed, 6 insertions(+), 16 deletions(-)

diff --git a/drivers/gpu/drm/pl111/pl111_display.c b/drivers/gpu/drm/pl111/pl111_display.c
index 754f6b25f265..31eb62e4476f 100644
--- a/drivers/gpu/drm/pl111/pl111_display.c
+++ b/drivers/gpu/drm/pl111/pl111_display.c
@@ -196,23 +196,13 @@ static void pl111_display_enable(struct drm_simple_display_pipe *pipe,
const struct drm_bridge_timings *btimings = bridge->timings;

/*
- * Here is when things get really fun. Sometimes the bridge
- * timings are such that the signal out from PL11x is not
- * stable before the receiving bridge (such as a dumb VGA DAC
- * or similar) samples it. If that happens, we compensate by
- * the only method we have: output the data on the opposite
- * edge of the clock so it is for sure stable when it gets
- * sampled.
- *
- * The PL111 manual does not contain proper timining diagrams
- * or data for these details, but we know from experiments
- * that the setup time is more than 3000 picoseconds (3 ns).
- * If we have a bridge that requires the signal to be stable
- * earlier than 3000 ps before the clock pulse, we have to
- * output the data on the opposite edge to avoid flicker.
+ * Use LCD Timing 2 Register Invert Pixel Clock (IPC) bit
+ * to make sure to drive data on falling edge if requested
+ * by bridge.
*/
- if (btimings && btimings->setup_time_ps >= 3000)
- tim2 ^= TIM2_IPC;
+ if (btimings && btimings->input_bus_flags &
+ DRM_BUS_FLAG_PIXDATA_NEGEDGE)
+ tim2 |= TIM2_IPC;
}

tim2 |= cpl << 16;
--
2.18.0
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