Re: [PATCH 14/14 v5] drm/i915/intel_i2c: remove POSTING_READ() fromgmbus transfers
From: Daniel Kurtz
Date: Wed Mar 28 2012 - 09:22:03 EST
On Wed, Mar 28, 2012 at 9:05 PM, Chris Wilson <chris@xxxxxxxxxxxxxxxxxx> wrote:
> On Wed, 28 Mar 2012 20:51:57 +0800, Daniel Kurtz <djkurtz@xxxxxxxxxxxx> wrote:
>> The POSTING_READ() calls were originally added to make sure the writes
>> were flushed before any timing delays and across loops.
>> However, the normal I915_READ() and I915_WRITE() macros already call
>> readl() / writel(), which already have an explicit mb().
>> Now that the code has settled a bit, let's remove them.
>> Signed-off-by: Daniel Kurtz <djkurtz@xxxxxxxxxxxx>
>> drivers/gpu/drm/i915/intel_i2c.c | 5 -----
>> 1 files changed, 0 insertions(+), 5 deletions(-)
>> diff --git a/drivers/gpu/drm/i915/intel_i2c.c b/drivers/gpu/drm/i915/intel_i2c.c
>> index 2865313..be2852e 100644
>> --- a/drivers/gpu/drm/i915/intel_i2c.c
>> +++ b/drivers/gpu/drm/i915/intel_i2c.c
>> @@ -131,7 +131,6 @@ static void set_clock(void *data, int state_high)
>> I915_WRITE_NOTRACE(bus->gpio_reg, reserved | clock_bits);
>> - POSTING_READ(bus->gpio_reg);
> We do need the write flush here (and set_data) as the next action is a
> udelay loop which is not per-se a mb.
Now I am confused. I915_WRITE_NOTRACE() calls writel(), which has an
explicit mb(); Why do you need another mb?
> Chris Wilson, Intel Open Source Technology Centre
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