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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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