linux-kernel - Re: [PATCH] drm/amd/display: Fix unsigned expression compared with zero

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Date:   Thu, 7 Jul 2022 16:45:06 -0400
From:   Alex Deucher <alexdeucher@...il.com>
To:     Harry Wentland <harry.wentland@....com>
Cc:     Zhongjun Tan <hbut_tan@....com>,
        "Leo (Sunpeng) Li" <sunpeng.li@....com>,
        "Siqueira, Rodrigo" <Rodrigo.Siqueira@....com>,
        "Deucher, Alexander" <alexander.deucher@....com>,
        Christian Koenig <christian.koenig@....com>,
        xinhui pan <Xinhui.Pan@....com>,
        Dave Airlie <airlied@...ux.ie>,
        Daniel Vetter <daniel@...ll.ch>,
        Bas Nieuwenhuizen <bas@...nieuwenhuizen.nl>,
        cai.huoqing@...ux.dev, Zhongjun Tan <tanzhongjun@...lpad.com>,
        Maling list - DRI developers 
        <dri-devel@...ts.freedesktop.org>,
        amd-gfx list <amd-gfx@...ts.freedesktop.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] drm/amd/display: Fix unsigned expression compared with zero

On Thu, Jul 7, 2022 at 4:38 PM Harry Wentland <harry.wentland@....com> wrote:
>
>
>
> On 2022-07-07 14:22, Alex Deucher wrote:
> > On Wed, Jul 6, 2022 at 3:41 AM Zhongjun Tan <hbut_tan@....com> wrote:
> >>
> >> From: Zhongjun Tan <tanzhongjun@...lpad.com>
> >>
> >> Fix unsigned expression compared with zero
> >>
> >> Signed-off-by: Zhongjun Tan <tanzhongjun@...lpad.com>
> >> ---
> >>  .../gpu/drm/amd/display/dc/dml/dcn20/display_rq_dlg_calc_20.c | 4 ++--
> >>  1 file changed, 2 insertions(+), 2 deletions(-)
> >>
> >> diff --git a/drivers/gpu/drm/amd/display/dc/dml/dcn20/display_rq_dlg_calc_20.c b/drivers/gpu/drm/amd/display/dc/dml/dcn20/display_rq_dlg_calc_20.c
> >> index 548cdef8a8ad..21e4af38b8c1 100644
> >> --- a/drivers/gpu/drm/amd/display/dc/dml/dcn20/display_rq_dlg_calc_20.c
> >> +++ b/drivers/gpu/drm/amd/display/dc/dml/dcn20/display_rq_dlg_calc_20.c
> >> @@ -244,8 +244,8 @@ static void handle_det_buf_split(struct display_mode_lib *mode_lib,
> >>         bool req128_c = false;
> >>         bool surf_linear = (pipe_src_param->sw_mode == dm_sw_linear);
> >>         bool surf_vert = (pipe_src_param->source_scan == dm_vert);
> >> -       unsigned int log2_swath_height_l = 0;
> >> -       unsigned int log2_swath_height_c = 0;
> >> +       int log2_swath_height_l = 0;
> >> +       int log2_swath_height_c = 0;
> >
> > @Wentland, Harry Can you comment on the required range needed for
> > these integers?  Maybe it would be better to just drop the comparisons
> > with 0.
> >
>
> I'm not sure I see the problem we're trying to fix.
> An unsigned int can be 0, so a x != 0 or x > 0 check
> is still a valid check.

Hmm, you are right.  I swear I had seen a >= 0 check in that code, but
now I can't find it.  Sorry for the noise.

Alex

>
> Harry
>
> > Alex
> >
> >>         unsigned int detile_buf_size_in_bytes = mode_lib->ip.det_buffer_size_kbytes * 1024;
> >>
> >>         full_swath_bytes_packed_l = rq_param->misc.rq_l.full_swath_bytes;
> >> --
> >> 2.29.0
> >>
>