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    SubjectRe: [PATCH 13/13 v4] drm/i915/intel_i2c: reuse GMBUS2 value read in polling loop
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    On Wed, 28 Mar 2012 02:36:22 +0800, Daniel Kurtz <djkurtz@chromium.org> wrote:
    > Save the GMBUS2 value read while polling for state changes, and then
    > reuse this value when determining for which reason the loops were exited.
    > This is a small optimization which saves a couple of bus accesses for
    > memory mapped IO registers.
    >
    > To avoid "assigning in if clause" checkpatch errors", use a ret variable
    > to store the wait_for macro return value.
    >
    > Signed-off-by: Daniel Kurtz <djkurtz@chromium.org>
    > ---
    > drivers/gpu/drm/i915/intel_i2c.c | 32 ++++++++++++++++++++------------
    > 1 files changed, 20 insertions(+), 12 deletions(-)
    >
    > diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
    > index c71f3dc..174fc71 100644
    > --- a/drivers/gpu/drm/i915/intel_i2c.c
    > +++ b/drivers/gpu/drm/i915/intel_i2c.c
    > @@ -210,6 +210,7 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
    > int reg_offset = dev_priv->gpio_mmio_base;
    > u16 len = msg->len;
    > u8 *buf = msg->buf;
    > + u32 gmbus2;
    Does the temporary really need such broad scoping?

    > I915_WRITE(GMBUS1 + reg_offset,
    > gmbus1 |
    > @@ -219,13 +220,15 @@ gmbus_xfer_read(struct drm_i915_private *dev_priv, struct i2c_msg *msg,
    > GMBUS_SLAVE_READ | GMBUS_SW_RDY);
    > POSTING_READ(GMBUS2 + reg_offset);
    Might as well shave this read as well.

    > do {
    > + int ret;
    > u32 val, loop = 0;
    >
    > - if (wait_for(I915_READ(GMBUS2 + reg_offset) &
    > - (GMBUS_SATOER | GMBUS_HW_RDY),
    > - 50))
    > + ret = wait_for((gmbus2 = I915_READ(GMBUS2 + reg_offset)) &
    > + (GMBUS_SATOER | GMBUS_HW_RDY),
    > + 50);
    > + if (ret)
    > return -ETIMEDOUT;
    > - if (I915_READ(GMBUS2 + reg_offset) & GMBUS_SATOER)
    > + if (gmbus2 & GMBUS_SATOER)
    > return -ENXIO;
    >
    > val = I915_READ(GMBUS3 + reg_offset);
    > @@ -245,6 +248,7 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
    > u16 len = msg->len;
    > u8 *buf = msg->buf;
    > u32 val, loop;
    > + u32 gmbus2;
    >
    > val = loop = 0;
    > while (len && loop < 4) {
    > @@ -260,6 +264,7 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
    > GMBUS_SLAVE_WRITE | GMBUS_SW_RDY);
    > POSTING_READ(GMBUS2 + reg_offset);
    > while (len) {
    > + int ret;
    > val = loop = 0;
    > do {
    > val |= *buf++ << (8 * loop);
    > @@ -268,11 +273,12 @@ gmbus_xfer_write(struct drm_i915_private *dev_priv, struct i2c_msg *msg)
    > I915_WRITE(GMBUS3 + reg_offset, val);
    > POSTING_READ(GMBUS2 + reg_offset);

    And here.

    --
    Chris Wilson, Intel Open Source Technology Centre


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