linux-kernel - Re: [PATCH] drm/amdgpu/gfx10: remove redundant repeated null checks

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Message-ID: <CADnq5_PdgH7yPZ9UNw3iXvuQAAUmuKpMh-E8NLri_q5Zn8deWQ@mail.gmail.com>
Date: Mon, 4 Aug 2025 13:25:23 -0400
From: Alex Deucher <alexdeucher@...il.com>
To: Dan Carpenter <dan.carpenter@...aro.org>
Cc: Ethan Carter Edwards <ethan@...ancedwards.com>, Alex Deucher <alexander.deucher@....com>, 
	Christian König <christian.koenig@....com>, 
	David Airlie <airlied@...il.com>, Simona Vetter <simona@...ll.ch>, amd-gfx@...ts.freedesktop.org, 
	dri-devel@...ts.freedesktop.org, linux-kernel@...r.kernel.org, 
	kernel-janitors@...r.kernel.org
Subject: Re: [PATCH] drm/amdgpu/gfx10: remove redundant repeated null checks

On Mon, Aug 4, 2025 at 1:15 PM Dan Carpenter <dan.carpenter@...aro.org> wrote:
>
> On Mon, Aug 04, 2025 at 11:08:57AM -0400, Alex Deucher wrote:
> > On Mon, Aug 4, 2025 at 10:49 AM Dan Carpenter <dan.carpenter@...aro.org> wrote:
> > >
> > > On Mon, Aug 04, 2025 at 10:32:43AM -0400, Alex Deucher wrote:
> > > > On Sat, Aug 2, 2025 at 4:22 AM Ethan Carter Edwards
> > > > <ethan@...ancedwards.com> wrote:
> > > > >
> > > > > The repeated checks on grbm_soft_reset are unnecessary. Remove them.
> > > > >
> > > >
> > > > These are not NULL checks and they are necessary.  The code is
> > > > checking if any bits are set in that register.  If not, then we can
> > > > skip that code as there is nothing to do.
> > > >
> > >
> > > It's not a null check, but it is a nested check and it's a local
> > > variable so the patch is correct enough.  At this point we know that
> > > grbm_soft_reset can't be zero.
> >
> > It can be 0 as far as I can see.  If none of the GRBM_STATUS bits are
> > set, then we never set any of the bits in grbm_soft_reset.
> >
>
> You're missing the first check...
>
> drivers/gpu/drm/amd/amdgpu/gfx_v10_0.c
>   7657          if (grbm_soft_reset) {
>                     ^^^^^^^^^^^^^^^
> Checked.
>
>   7658                  /* stop the rlc */
>   7659                  gfx_v10_0_rlc_stop(adev);
>   7660
>   7661                  /* Disable GFX parsing/prefetching */
>   7662                  gfx_v10_0_cp_gfx_enable(adev, false);
>   7663
>   7664                  /* Disable MEC parsing/prefetching */
>   7665                  gfx_v10_0_cp_compute_enable(adev, false);
>   7666
>   7667                  if (grbm_soft_reset) {
>                             ^^^^^^^^^^^^^^^
> Unnecessary.

Yes, sorry, my brain processed this as the first check.

Alex

>
>   7668                          tmp = RREG32_SOC15(GC, 0, mmGRBM_SOFT_RESET);
>   7669                          tmp |= grbm_soft_reset;
>   7670                          dev_info(adev->dev, "GRBM_SOFT_RESET=0x%08X\n", tmp);
>   7671                          WREG32_SOC15(GC, 0, mmGRBM_SOFT_RESET, tmp);
>   7672                          tmp = RREG32_SOC15(GC, 0, mmGRBM_SOFT_RESET);
>   7673
>   7674                          udelay(50);
>   7675
>   7676                          tmp &= ~grbm_soft_reset;
>   7677                          WREG32_SOC15(GC, 0, mmGRBM_SOFT_RESET, tmp);
>   7678                          tmp = RREG32_SOC15(GC, 0, mmGRBM_SOFT_RESET);
>   7679                  }
>   7680
>   7681                  /* Wait a little for things to settle down */
>   7682                  udelay(50);
>   7683          }
>   7684          return 0;
>
> regards,
> dan carpenter
>