Re: [Intel-gfx] [PATCH v2 2/8] drm/i915: Add more control to wait_for routines

[Chris Wilson]

Quoting Sean Paul (2017-12-01 17:20:24)
>  /**
> - * _wait_for - magic (register) wait macro
> + * __wait_for - magic wait macro
>   *
> - * Does the right thing for modeset paths when run under kdgb or similar atomic
> - * contexts. Note that it's important that we check the condition again after
> + * Macro to help avoid open coding check/wait/timeout patterns, will do the
> + * right think wrt to choosing msleep vs usleep_range based on how long the wait
> + * interval is. Note that it's important that we check the condition again after
>   * having timed out, since the timeout could be due to preemption or similar and
>   * we've never had a chance to check the condition before the timeout.
>   */
> -#define _wait_for(COND, US, W) ({ \
> +#define __wait_for(OP, COND, US, W) ({ \
>         unsigned long timeout__ = jiffies + usecs_to_jiffies(US) + 1;   \
>         int ret__;                                                      \
>         might_sleep();                                                  \
>         for (;;) {                                                      \
>                 bool expired__ = time_after(jiffies, timeout__);        \
> +               OP;                                                     \
>                 if (COND) {                                             \
>                         ret__ = 0;                                      \
>                         break;                                          \
> @@ -62,11 +64,16 @@
>                         ret__ = -ETIMEDOUT;                             \
>                         break;                                          \
>                 }                                                       \
> -               usleep_range((W), (W) * 2);                             \
> +               if (W > (20 * 1000))                                    \
> +                       msleep(W / 1000);                               \
> +               else                                                    \
> +                       usleep_range((W), (W) * 2);                     \

The current wait_for() is a little more complicated nowadays (variable
W).

Are ms intervals going to be that common? Using a state-machine springs
to mind, but you could argue that msleep() is just a yield. Using msleep
though is going to leave D processes visible and a bump in load :|

>         }                                                               \
>         ret__;                                                          \
>  })
>  
> +#define _wait_for(COND, US, W)         __wait_for(;,(COND), US, W)
> +
>  #define wait_for(COND, MS)             _wait_for((COND), (MS) * 1000, 1000)
>  
>  /* If CONFIG_PREEMPT_COUNT is disabled, in_atomic() always reports false. */
> diff --git a/drivers/gpu/drm/i915/intel_uncore.c b/drivers/gpu/drm/i915/intel_uncore.c
> index b4621271e7a2..c851b0c0602d 100644
> --- a/drivers/gpu/drm/i915/intel_uncore.c
> +++ b/drivers/gpu/drm/i915/intel_uncore.c
> @@ -1770,12 +1770,14 @@ int __intel_wait_for_register_fw(struct drm_i915_private *dev_priv,
>  }
>  
>  /**
> - * intel_wait_for_register - wait until register matches expected state
> + * __intel_wait_for_register - wait until register matches expected state
>   * @dev_priv: the i915 device
>   * @reg: the register to read
>   * @mask: mask to apply to register value
>   * @value: expected value
> - * @timeout_ms: timeout in millisecond
> + * @fast_timeout_us: fast timeout in microsecond for atomic/tight wait
> + * @slow_timeout_ms: slow timeout in millisecond
> + * @out_value: optional placeholder to hold registry value
>   *
>   * This routine waits until the target register @reg contains the expected
>   * @value after applying the @mask, i.e. it waits until ::
> @@ -1786,15 +1788,18 @@ int __intel_wait_for_register_fw(struct drm_i915_private *dev_priv,
>   *
>   * Returns 0 if the register matches the desired condition, or -ETIMEOUT.
>   */
> -int intel_wait_for_register(struct drm_i915_private *dev_priv,
> +int __intel_wait_for_register(struct drm_i915_private *dev_priv,
>                             i915_reg_t reg,
>                             u32 mask,
>                             u32 value,
> -                           unsigned int timeout_ms)
> +                           unsigned int fast_timeout_us,
> +                           unsigned int slow_timeout_ms,
> +                           u32 *out_value)
>  {
>         unsigned fw =
>                 intel_uncore_forcewake_for_reg(dev_priv, reg, FW_REG_READ);
>         int ret;
> +       u32 reg_value;
>  
>         might_sleep();
>  
> @@ -1803,14 +1808,18 @@ int intel_wait_for_register(struct drm_i915_private *dev_priv,
>  
>         ret = __intel_wait_for_register_fw(dev_priv,
>                                            reg, mask, value,
> -                                          2, 0, NULL);
> +                                          fast_timeout_us, 0, &reg_value);
>  
>         intel_uncore_forcewake_put__locked(dev_priv, fw);
>         spin_unlock_irq(&dev_priv->uncore.lock);
>  
>         if (ret)
> -               ret = wait_for((I915_READ_NOTRACE(reg) & mask) == value,
> -                              timeout_ms);
> +               ret = __wait_for(reg_value = I915_READ_NOTRACE(reg),
> +                                (reg_value & mask) == value,
> +                                slow_timeout_ms * 1000, 1000);
> +
> +       if (out_value)
> +               *out_value = reg_value;

Looks good.
-Chris