[PATCH V2] drm/i915: relax uncritical udelay_range()

Nicholas Mc Guire
2016-12-16T01:59:38Z

udelay_range(1, 2) is inefficient and as discussions with Jani Nikula
<jani.nikula@linux.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@osadl.org>
---

V2: use relaxed uslee_range() rather than udelay
fix documentation of changed timings

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-20161215)

drivers/gpu/drm/i915/intel_dsi_pll.c | 6 ++++--
1 file changed, 4 insertions(+), 2 deletions(-)

diff --git a/drivers/gpu/drm/i915/intel_dsi_pll.c b/drivers/gpu/drm/i915/intel_dsi_pll.c
index 56eff60..d210bc4 100644
--- a/drivers/gpu/drm/i915/intel_dsi_pll.c
+++ b/drivers/gpu/drm/i915/intel_dsi_pll.c
@@ -156,8 +156,10 @@ static void vlv_enable_dsi_pll(struct intel_encoder *encoder,
vlv_cck_write(dev_priv, CCK_REG_DSI_PLL_CONTROL,
config->dsi_pll.ctrl & ~DSI_PLL_VCO_EN);

- /* 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);

vlv_cck_write(dev_priv, CCK_REG_DSI_PLL_CONTROL, config->dsi_pll.ctrl);

--
2.1.4