Re: [PATCH] drm/amdgpu: Senseless code and unnecessary memset

[Christian König]

Am 06.04.22 um 16:26 schrieb Jani Nikula:
> On Tue, 05 Apr 2022, Christian König <christian.koenig@xxxxxxx> wrote:
> > Am 05.04.22 um 19:36 schrieb Grigory Vasilyev:
> > > Using memset on local arrays before exiting the function is pointless.
> > > Compilator will remove this code. Also for local arrays is preferable to
> > > use {0} instead of memset. Mistakes are often made when working with
> > > memset.
> > Well actually memset is preferred when working with structures which are
> > given to the hardware parser because {0} won't initialize paddings.
> Not that I'd know anything that's going on here... but it sure seems
> strange to me to be passing unpacked structures where the padding might
> matter to a "hardware parser".

Well to me it is an absolute miracle why the heck compilers don't 
initialize paddings.

We had so many ups moments over the years and I really don't see why it 
should be more optimal to do this.

Anyway, the memset() is used intentionally here and I don't really want 
to change it. What we could do is removing the second superfluous memset 
and use sizeof() instead of hard coding the size.

Regards,
Christian.

> *shrug*
>
>
> BR,
> Jani.
>
>
> > So please don't use {0} in any of the atom bios code.
> >
> > Regards,
> > Christian.
> >
> > > Signed-off-by: Grigory Vasilyev <h0tc0d3@xxxxxxxxx>
> > > ---
> > >    drivers/gpu/drm/amd/amdgpu/atom.c | 8 +-------
> > >    1 file changed, 1 insertion(+), 7 deletions(-)
> > >
> > > diff --git a/drivers/gpu/drm/amd/amdgpu/atom.c b/drivers/gpu/drm/amd/amdgpu/atom.c
> > > index be9d61bcb8ae..537e48fbbe6b 100644
> > > --- a/drivers/gpu/drm/amd/amdgpu/atom.c
> > > +++ b/drivers/gpu/drm/amd/amdgpu/atom.c
> > > @@ -1538,11 +1538,9 @@ struct atom_context *amdgpu_atom_parse(struct card_info *card, void *bios)
> > >    int amdgpu_atom_asic_init(struct atom_context *ctx)
> > >    {
> > >    	int hwi = CU16(ctx->data_table + ATOM_DATA_FWI_PTR);
> > > -	uint32_t ps[16];
> > > +	uint32_t ps[16] = {0};
> > >    	int ret;
> > >    
> > > -	memset(ps, 0, 64);
> > > -
> > >    	ps[0] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFSCLK_PTR));
> > >    	ps[1] = cpu_to_le32(CU32(hwi + ATOM_FWI_DEFMCLK_PTR));
> > >    	if (!ps[0] || !ps[1])
> > > @@ -1551,10 +1549,6 @@ int amdgpu_atom_asic_init(struct atom_context *ctx)
> > >    	if (!CU16(ctx->cmd_table + 4 + 2 * ATOM_CMD_INIT))
> > >    		return 1;
> > >    	ret = amdgpu_atom_execute_table(ctx, ATOM_CMD_INIT, ps);
> > > -	if (ret)
> > > -		return ret;
> > > -
> > > -	memset(ps, 0, 64);
> > >    
> > >    	return ret;
> > >    }