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From:   Jani Nikula <jani.nikula@intel.com>
To:     Christian =?utf-8?Q?K=C3=B6nig?= <christian.koenig@amd.com>,
        Grigory Vasilyev <h0tc0d3@gmail.com>,
        Rodrigo Siqueira <Rodrigo.Siqueira@amd.com>,
        Melissa Wen <mwen@igalia.com>
Cc:     Alex Deucher <alexander.deucher@amd.com>,
        "Pan, Xinhui" <Xinhui.Pan@amd.com>,
        David Airlie <airlied@linux.ie>,
        Daniel Vetter <daniel@ffwll.ch>, Jiawei Gu <Jiawei.Gu@amd.com>,
        Lucas De Marchi <lucas.demarchi@intel.com>,
        amd-gfx@lists.freedesktop.org, dri-devel@lists.freedesktop.org,
        linux-kernel@vger.kernel.org
Subject: Re: [PATCH] drm/amdgpu: Senseless code and unnecessary memset
In-Reply-To: <614a4844-fa5d-8b8e-0628-894394f31608@amd.com>
Organization: Intel Finland Oy - BIC 0357606-4 - Westendinkatu 7, 02160 Espoo
References: <20220405173632.2663-1-h0tc0d3@gmail.com>
 <614a4844-fa5d-8b8e-0628-894394f31608@amd.com>
Date:   Wed, 06 Apr 2022 17:26:44 +0300
Message-ID: <874k3670ez.fsf@intel.com>
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On Tue, 05 Apr 2022, Christian K=C3=B6nig <christian.koenig@amd.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=
=20
> 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".

*shrug*


BR,
Jani.


>
> So please don't use {0} in any of the atom bios code.
>
> Regards,
> Christian.
>
>>
>> Signed-off-by: Grigory Vasilyev <h0tc0d3@gmail.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/amd=
gpu/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 car=
d_info *card, void *bios)
>>   int amdgpu_atom_asic_init(struct atom_context *ctx)
>>   {
>>   	int hwi =3D CU16(ctx->data_table + ATOM_DATA_FWI_PTR);
>> -	uint32_t ps[16];
>> +	uint32_t ps[16] =3D {0};
>>   	int ret;
>>=20=20=20
>> -	memset(ps, 0, 64);
>> -
>>   	ps[0] =3D cpu_to_le32(CU32(hwi + ATOM_FWI_DEFSCLK_PTR));
>>   	ps[1] =3D 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 *ct=
x)
>>   	if (!CU16(ctx->cmd_table + 4 + 2 * ATOM_CMD_INIT))
>>   		return 1;
>>   	ret =3D amdgpu_atom_execute_table(ctx, ATOM_CMD_INIT, ps);
>> -	if (ret)
>> -		return ret;
>> -
>> -	memset(ps, 0, 64);
>>=20=20=20
>>   	return ret;
>>   }
>

--=20
Jani Nikula, Intel Open Source Graphics Center