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

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Date:   Thu, 5 Nov 2020 11:25:11 -0800
From:   Eric Anholt <eric@...olt.net>
To:     Deepak R Varma <mh12gx2825@...il.com>
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 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.