linux-kernel - [PATCH 3.16 002/212] drm/i915: relax uncritical udelay

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Date:   Thu, 01 Jun 2017 16:43:15 +0100
From:   Ben Hutchings <ben@...adent.org.uk>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
CC:     akpm@...ux-foundation.org, "Jani Nikula" <jani.nikula@...el.com>,
        "Nicholas Mc Guire" <hofrat@...dl.org>
Subject: [PATCH 3.16 002/212] drm/i915: relax uncritical udelay_range()

3.16.44-rc1 review patch.  If anyone has any objections, please let me know.

------------------

From: Nicholas Mc Guire <hofrat@...dl.org>

commit 15a43cbf4736a3932e6259fa7d6e47558f6222b0 upstream.

udelay_range(1, 2) is inefficient and as discussions with Jani Nikula
<jani.nikula@...ux.intel.com> unnecessary here. This replaces this
tight setting with a relaxed delay of min=20 and max=50 which helps
the hrtimer subsystem optimize timer handling.

Fixes: commit be4fc046bed3 ("drm/i915: add VLV DSI PLL Calculations")
Link: http://lkml.org/lkml/2016/12/15/147
Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
Reviewed-by: Jani Nikula <jani.nikula@...el.com>
Signed-off-by: Jani Nikula <jani.nikula@...el.com>
Link: http://patchwork.freedesktop.org/patch/msgid/1481853578-19834-1-git-send-email-hofrat@osadl.org
Signed-off-by: Ben Hutchings <ben@...adent.org.uk>
---
 drivers/gpu/drm/i915/intel_dsi_pll.c | 6 ++++--
 1 file changed, 4 insertions(+), 2 deletions(-)

--- a/drivers/gpu/drm/i915/intel_dsi_pll.c
+++ b/drivers/gpu/drm/i915/intel_dsi_pll.c
@@ -265,8 +265,10 @@ void vlv_enable_dsi_pll(struct intel_enc
 
 	vlv_configure_dsi_pll(encoder);
 
-	/* wait at least 0.5 us after ungating before enabling VCO */
-	usleep_range(1, 10);
+	/* wait at least 0.5 us after ungating before enabling VCO,
+	 * allow hrtimer subsystem optimization by relaxing timing
+	 */
+	usleep_range(10, 50);
 
 	tmp = vlv_cck_read(dev_priv, CCK_REG_DSI_PLL_CONTROL);
 	tmp |= DSI_PLL_VCO_EN;