linux-kernel - Re: [PATCH] drm/vc4: replace idr_init() by idr_init

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Date:   Fri, 6 Nov 2020 01:03:12 +0530
From:   Deepak R Varma <mh12gx2825@...il.com>
To:     Eric Anholt <eric@...olt.net>
Cc:     David Airlie <airlied@...ux.ie>, Daniel Vetter <daniel@...ll.ch>,
        DRI Development <dri-devel@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Maxime Ripard <maxime@...no.tech>,
        Maxime Ripard <mripard@...nel.org>
Subject: Re: [PATCH] drm/vc4: replace idr_init() by idr_init_base()

On Thu, Nov 05, 2020 at 11:25:11AM -0800, Eric Anholt wrote:
> On Thu, Nov 5, 2020 at 10:25 AM Deepak R Varma <mh12gx2825@...il.com> wrote:
> >
> > idr_init() uses base 0 which is an invalid identifier for this driver.
> > The idr_alloc for this driver uses VC4_PERFMONID_MIN as start value for
> > ID range and it is #defined to 1. The new function idr_init_base allows
> > IDR to set the ID lookup from base 1. This avoids all lookups that
> > otherwise starts from 0 since 0 is always unused / available.
> >
> > References: commit 6ce711f27500 ("idr: Make 1-based IDRs more efficient")
> >
> > Signed-off-by: Deepak R Varma <mh12gx2825@...il.com>
> > ---
> >  drivers/gpu/drm/vc4/vc4_perfmon.c | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> >
> > diff --git a/drivers/gpu/drm/vc4/vc4_perfmon.c b/drivers/gpu/drm/vc4/vc4_perfmon.c
> > index f4aa75efd16b..7d40f421d922 100644
> > --- a/drivers/gpu/drm/vc4/vc4_perfmon.c
> > +++ b/drivers/gpu/drm/vc4/vc4_perfmon.c
> > @@ -77,7 +77,7 @@ struct vc4_perfmon *vc4_perfmon_find(struct vc4_file *vc4file, int id)
> >  void vc4_perfmon_open_file(struct vc4_file *vc4file)
> >  {
> >         mutex_init(&vc4file->perfmon.lock);
> > -       idr_init(&vc4file->perfmon.idr);
> > +       idr_init_base(&vc4file->perfmon.idr, 1);
> >  }
> 
> Sounds like you should use VC4_PERFMONID_MIN instead of a magic 1 here.

Agreed. I will update and resend v2.

Thank you,
./drv