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

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Message-ID: <874k3670ez.fsf@intel.com>
Date:   Wed, 06 Apr 2022 17:26:44 +0300
From:   Jani Nikula <jani.nikula@...el.com>
To:     Christian König <christian.koenig@....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

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".

*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;
>>   }
>

-- 
Jani Nikula, Intel Open Source Graphics Center