[Intel-gfx] [PATCH 1/2] drm/i915/display: use fetch_and_zero if applicable

[Vivi, Rodrigo]

On Thu, 2022-12-08 at 14:32 +0200, Jani Nikula wrote:
> On Thu, 08 Dec 2022, Andrzej Hajda <andrzej.hajda at intel.com> 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.

+1 here.

Please let's go the other way around and try to kill macros like this.

we either kill or we ensure this gets accepted in the core kernel
libraries.

> 
> 
> BR,
> Jani.
> 
> 
> > 
> > Signed-off-by: Andrzej Hajda <andrzej.hajda at intel.com>
> > ---
> >  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);
>