[PATCH 02/34] drm: Convert aux_idr to XArray

[Matthew Wilcox]

On Mon, Feb 25, 2019 at 07:57:33PM +0200, Ville Syrjälä wrote:
> On Thu, Feb 21, 2019 at 10:41:23AM -0800, Matthew Wilcox wrote:
> > @@ -49,8 +49,7 @@ struct drm_dp_aux_dev {
> >  
> >  #define DRM_AUX_MINORS	256
> >  #define AUX_MAX_OFFSET	(1 << 20)
> > -static DEFINE_IDR(aux_idr);
> > -static DEFINE_MUTEX(aux_idr_mutex);
> > +static DEFINE_XARRAY_ALLOC(aux_xa);
> >  static struct class *drm_dp_aux_dev_class;
> >  static int drm_dev_major = -1;
[...]
> >  static struct drm_dp_aux_dev *alloc_drm_dp_aux_dev(struct drm_dp_aux *aux)
> >  {
> > +	static u32 next;
> 
> Is there a particular reason for that being static?

It needs to maintain its value between function calls so that we know
where to start allocating from the next time we call xa_alloc_cyclic().
It can either live here with a short name, or we could put it at file
scope with a descriptive name (probably aux_xa_next).  It's up to you
which you think is better; it's your driver.

The IDR embedded the 'next' value in the struct idr, but that was
overhead paid by all users of the IDR rather than the very few that
called idr_alloc_cyclic().

> > +	err = xa_alloc_cyclic(&aux_xa, &aux_dev->index, aux_dev,
> > +			XA_LIMIT(0, DRM_AUX_MINORS), &next, GFP_KERNEL);
> > +	if (err < 0) {
> >  		kfree(aux_dev);