Re: [PATCH 14/14 v5] drm/i915/intel_i2c: remove POSTING_READ() from gmbus transfers

Daniel Kurtz
2012-03-28T13:22:06Z

On Wed, Mar 28, 2012 at 9:05 PM, Chris Wilson <chris@chris-wilson.co.uk> wrote:
> On Wed, 28 Mar 2012 20:51:57 +0800, Daniel Kurtz <djkurtz@chromium.org> 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@chromium.org>
>> ---
>>  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)
>>                       GPIO_CLOCK_VAL_MASK;
>>
>>       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
>
> --
> Chris Wilson, Intel Open Source Technology Centre