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[3/3] drm: arcpgu: Allow some clock deviation in crtc->mode_valid() callback

Message ID 8fa18dc1acf77d79dd928037cf827749328cc5b6.1500293127.git.joabreu@synopsys.com (mailing list archive)
State New, archived
Headers show

Commit Message

Jose Abreu July 17, 2017, 12:08 p.m. UTC 
Currently we expect that clock driver produces the exact same value
as we are requiring. There can, and will, be some deviation
however so we need to take that into account instead of just
rejecting the mode.

According to the HDMI spec we have a max of +-0.5% for the pixel clock
frequency deviation. Lets take that into an advantage and use it to
calculate how much deviation we can support.

Signed-off-by: Jose Abreu <joabreu@synopsys.com>
Acked-by: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Carlos Palminha <palminha@synopsys.com>
Cc: Alexey Brodkin <abrodkin@synopsys.com>
Cc: Daniel Vetter <daniel.vetter@intel.com>
Cc: Dave Airlie <airlied@gmail.com>
---
 drivers/gpu/drm/arc/arcpgu_crtc.c | 7 ++++---
 1 file changed, 4 insertions(+), 3 deletions(-)
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Patch

diff --git a/drivers/gpu/drm/arc/arcpgu_crtc.c b/drivers/gpu/drm/arc/arcpgu_crtc.c
index 1859dd3..55c5d5b 100644
--- a/drivers/gpu/drm/arc/arcpgu_crtc.c
+++ b/drivers/gpu/drm/arc/arcpgu_crtc.c
@@ -69,12 +69,13 @@  static enum drm_mode_status arc_pgu_crtc_mode_valid(struct drm_crtc *crtc,
 {
 	struct arcpgu_drm_private *arcpgu = crtc_to_arcpgu_priv(crtc);
 	long rate, clk_rate = mode->clock * 1000;
+	long diff = clk_rate / 200; /* +-0.5% allowed by HDMI spec */
 
 	rate = clk_round_rate(arcpgu->clk, clk_rate);
-	if (rate != clk_rate)
-		return MODE_NOCLOCK;
+	if ((max(rate, clk_rate) - min(rate, clk_rate) < diff) && (rate > 0))
+		return MODE_OK;
 
-	return MODE_OK;
+	return MODE_NOCLOCK;
 }
 
 static void arc_pgu_crtc_mode_set_nofb(struct drm_crtc *crtc)