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Message-ID: <f742b6b8-4056-543c-17a5-ae373ca71b45@amd.com>
Date: Wed, 6 Apr 2022 16:43:15 +0200
From: Christian König <christian.koenig@....com>
To: Jani Nikula <jani.nikula@...el.com>,
Grigory Vasilyev <h0tc0d3@...il.com>,
Rodrigo Siqueira <Rodrigo.Siqueira@....com>,
Melissa Wen <mwen@...lia.com>
Cc: Alex Deucher <alexander.deucher@....com>,
"Pan, Xinhui" <Xinhui.Pan@....com>,
David Airlie <airlied@...ux.ie>,
Daniel Vetter <daniel@...ll.ch>, Jiawei Gu <Jiawei.Gu@....com>,
Lucas De Marchi <lucas.demarchi@...el.com>,
amd-gfx@...ts.freedesktop.org, dri-devel@...ts.freedesktop.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH] drm/amdgpu: Senseless code and unnecessary memset
Am 06.04.22 um 16:26 schrieb Jani Nikula:
> On Tue, 05 Apr 2022, Christian König <christian.koenig@....com> 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@...il.com>
>>> ---
>>> 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;
>>> }
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