On Thu, 08 Dec 2022, Andrzej Hajda <andrzej.hajda@xxxxxxxxx> wrote:
> Simplify the code.
Personally, I absolutely hate fetch_and_zero().
I understand the point, but there are two main traps:
First, the name implies atomicity, which there is none at all.
Second, the name implies it's part of a kernel core header, which it
isn't, and this just amplifies the first point.
It's surprising and misleading, and those are not things I like about
interfaces in the kernel.
I would not like to see this proliferate. If fetch_and_zero() was atomic
*and* part of a core kernel header, it would be a different matter. But
I don't think that's going to happen, exactly because it won't be atomic
and the name implies it is.
BR,
Jani.
>
> Signed-off-by: Andrzej Hajda <andrzej.hajda@xxxxxxxxx>
> ---
> drivers/gpu/drm/i915/display/intel_hotplug.c | 12 ++++--------
> 1 file changed, 4 insertions(+), 8 deletions(-)
>
> diff --git a/drivers/gpu/drm/i915/display/intel_hotplug.c b/drivers/gpu/drm/i915/display/intel_hotplug.c
> index 907ab7526cb478..2972d7533da44e 100644
> --- a/drivers/gpu/drm/i915/display/intel_hotplug.c
> +++ b/drivers/gpu/drm/i915/display/intel_hotplug.c
> @@ -304,10 +304,8 @@ static void i915_digport_work_func(struct work_struct *work)
> u32 old_bits = 0;
>
> spin_lock_irq(&dev_priv->irq_lock);
> - long_port_mask = dev_priv->display.hotplug.long_port_mask;
> - dev_priv->display.hotplug.long_port_mask = 0;
> - short_port_mask = dev_priv->display.hotplug.short_port_mask;
> - dev_priv->display.hotplug.short_port_mask = 0;
> + long_port_mask = fetch_and_zero(&dev_priv->display.hotplug.long_port_mask);
> + short_port_mask = fetch_and_zero(&dev_priv->display.hotplug.short_port_mask);
> spin_unlock_irq(&dev_priv->irq_lock);
>
> for_each_intel_encoder(&dev_priv->drm, encoder) {
> @@ -379,10 +377,8 @@ static void i915_hotplug_work_func(struct work_struct *work)
>
> spin_lock_irq(&dev_priv->irq_lock);
>
> - hpd_event_bits = dev_priv->display.hotplug.event_bits;
> - dev_priv->display.hotplug.event_bits = 0;
> - hpd_retry_bits = dev_priv->display.hotplug.retry_bits;
> - dev_priv->display.hotplug.retry_bits = 0;
> + hpd_event_bits = fetch_and_zero(&dev_priv->display.hotplug.event_bits);
> + hpd_retry_bits = fetch_and_zero(&dev_priv->display.hotplug.retry_bits);
>
> /* Enable polling for connectors which had HPD IRQ storms */
> intel_hpd_irq_storm_switch_to_polling(dev_priv);
--
Jani Nikula, Intel Open Source Graphics Center
