linux-kernel - [PATCH] drm/i915: use udelay for very short delays

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Date:   Thu, 15 Dec 2016 05:29:07 +0100
From:   Nicholas Mc Guire <hofrat@...dl.org>
To:     Daniel Vetter <daniel.vetter@...el.com>
Cc:     Shashank Sharma <shashank.sharma@...el.com>,
        Jani Nikula <jani.nikula@...ux.intel.com>,
        David Airlie <airlied@...ux.ie>,
        intel-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
        linux-kernel@...r.kernel.org, Nicholas Mc Guire <hofrat@...dl.org>
Subject: [PATCH] drm/i915: use udelay for very short delays

Even on fast systems a 2 microsecond delay is most likely more efficient
as a busy-wait loop. The overhead of a hrtimer does not seem warranted -
change this to a udelay(2).

Signed-off-by: Nicholas Mc Guire <hofrat@...dl.org>
---

Problem found by coccinelle:

Patch was compile tested with: x86_64_defconfig (implies CONFIG_DRM_I915)

Patch is against 4.9.0 (localversion-next is next-20161214)

 drivers/gpu/drm/i915/intel_dsi.c | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/drivers/gpu/drm/i915/intel_dsi.c b/drivers/gpu/drm/i915/intel_dsi.c
index 5b72c50..19fe86b 100644
--- a/drivers/gpu/drm/i915/intel_dsi.c
+++ b/drivers/gpu/drm/i915/intel_dsi.c
@@ -379,7 +379,7 @@ static void bxt_dsi_device_ready(struct intel_encoder *encoder)
 		val &= ~ULPS_STATE_MASK;
 		val |= (ULPS_STATE_ENTER | DEVICE_READY);
 		I915_WRITE(MIPI_DEVICE_READY(port), val);
-		usleep_range(2, 3);
+		udelay(2);
 
 		/* 3. Exit ULPS */
 		val = I915_READ(MIPI_DEVICE_READY(port));
-- 
2.1.4