On Mon, Apr 10, 2023 at 03:35:09PM -0700, Ashutosh Dixit wrote:
> Instead of erroring out when GuC reset is in progress, block waiting for
> GuC reset to complete which is a more reasonable uapi behavior.
>
> v2: Avoid race between wake_up_all and waiting for wakeup (Rodrigo)
>
> Signed-off-by: Ashutosh Dixit <ashutosh.di...@intel.com>
> ---
> drivers/gpu/drm/i915/i915_hwmon.c | 38 +++++++++++++++++++++++++++----
> 1 file changed, 33 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/i915_hwmon.c
> b/drivers/gpu/drm/i915/i915_hwmon.c
> index 9ab8971679fe3..8471a667dfc71 100644
> --- a/drivers/gpu/drm/i915/i915_hwmon.c
> +++ b/drivers/gpu/drm/i915/i915_hwmon.c
> @@ -51,6 +51,7 @@ struct hwm_drvdata {
> char name[12];
> int gt_n;
> bool reset_in_progress;
> + wait_queue_head_t waitq;
> };
>
> struct i915_hwmon {
> @@ -395,16 +396,41 @@ hwm_power_max_read(struct hwm_drvdata *ddat, long *val)
> static int
> hwm_power_max_write(struct hwm_drvdata *ddat, long val)
> {
> +#define GUC_RESET_TIMEOUT msecs_to_jiffies(2000)
> +
> + int ret = 0, timeout = GUC_RESET_TIMEOUT;
> struct i915_hwmon *hwmon = ddat->hwmon;
> intel_wakeref_t wakeref;
> - int ret = 0;
> + DEFINE_WAIT(wait);
> u32 nval;
>
> - mutex_lock(&hwmon->hwmon_lock);
> - if (hwmon->ddat.reset_in_progress) {
> - ret = -EAGAIN;
> - goto unlock;
> + /* Block waiting for GuC reset to complete when needed */
> + for (;;) {
> + mutex_lock(&hwmon->hwmon_lock);
I'm really afraid of how this mutex is handled with the wait queue.
some initial thought it looks like it is trying to reimplement ww_mutex?
all other examples of the wait_queue usages like this or didn't use
locks or had it in a total different flow that I could not correlate.
> +
> + prepare_to_wait(&ddat->waitq, &wait, TASK_INTERRUPTIBLE);
> +
> + if (!hwmon->ddat.reset_in_progress)
> + break;
If this breaks we never unlock it?
> +
> + if (signal_pending(current)) {
> + ret = -EINTR;
> + break;
> + }
> +
> + if (!timeout) {
> + ret = -ETIME;
> + break;
> + }
> +
> + mutex_unlock(&hwmon->hwmon_lock);
do we need to lock the signal pending and timeout as well?
or only wrapping it around the hwmon->ddat access would be
enough?
> +
> + timeout = schedule_timeout(timeout);
> }
> + finish_wait(&ddat->waitq, &wait);
> + if (ret)
> + goto unlock;
> +
> wakeref = intel_runtime_pm_get(ddat->uncore->rpm);
>
> /* Disable PL1 limit and verify, because the limit cannot be disabled
> on all platforms */
> @@ -508,6 +534,7 @@ void i915_hwmon_power_max_restore(struct drm_i915_private
> *i915, bool old)
> intel_uncore_rmw(hwmon->ddat.uncore, hwmon->rg.pkg_rapl_limit,
> PKG_PWR_LIM_1_EN, old ? PKG_PWR_LIM_1_EN : 0);
> hwmon->ddat.reset_in_progress = false;
> + wake_up_all(&hwmon->ddat.waitq);
>
> mutex_unlock(&hwmon->hwmon_lock);
> }
> @@ -784,6 +811,7 @@ void i915_hwmon_register(struct drm_i915_private *i915)
> ddat->uncore = &i915->uncore;
> snprintf(ddat->name, sizeof(ddat->name), "i915");
> ddat->gt_n = -1;
> + init_waitqueue_head(&ddat->waitq);
>
> for_each_gt(gt, i915, i) {
> ddat_gt = hwmon->ddat_gt + i;
> --
> 2.38.0
>
