linux-kernel - Re: [PATCH v2 27/27] sound: ppc: remove unneeded memset after dma_alloc

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Message-ID: <ae51454e-68b1-bc82-8d8f-dbc273166dc3@c-s.fr>
Date:   Fri, 28 Jun 2019 11:48:37 +0200
From:   Christophe Leroy <christophe.leroy@....fr>
To:     Fuqian Huang <huangfq.daxian@...il.com>
Cc:     Rob Herring <robh@...nel.org>, alsa-devel@...a-project.org,
        linux-kernel@...r.kernel.org,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jaroslav Kysela <perex@...ex.cz>,
        Richard Fontana <rfontana@...hat.com>,
        Paul Mackerras <paulus@...ba.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        linuxppc-dev@...ts.ozlabs.org, Allison Randal <allison@...utok.net>
Subject: Re: [PATCH v2 27/27] sound: ppc: remove unneeded memset after
 dma_alloc_coherent



Le 28/06/2019 à 11:11, Fuqian Huang a écrit :
> The merge commit log tells (dma-mapping: zero memory returned from
> dma_alloc_* and deprecating the dma_zalloc_coherent).
> I used this commit just want to say that dma_alloc_coherent  has
> zeroed the allocated memory.
> Sorry for this mistake.
> 
> Maybe this commit 518a2f1925c3("dma-mapping: zero memory returned from
> dma_alloc_*") is correct.

Yes that looks appropriate. And it confirms it was already done on 
powerpc, as that patch doesn't include any change in powerpc arch.

Christophe

> 
> Christophe Leroy <christophe.leroy@....fr> 於 2019年6月28日週五 下午4:59寫道：
> 
>>
>>
>>
>> Le 28/06/2019 à 04:50, Fuqian Huang a écrit :
>>> In commit af7ddd8a627c
>>> ("Merge tag 'dma-mapping-4.21' of git://git.infradead.org/users/hch/dma-mapping"),
>>> dma_alloc_coherent has already zeroed the memory.
>>> So memset is not needed.
>>
>> You are refering to a merge commit, is that correct ?
>>
>> I can't see anything related in that commit, can you please pinpoint it ?
>>
>> As far as I can see, on powerpc the memory has always been zeroized
>> (since 2005 at least).
>>
>> Christophe
>>
>>>
>>> Signed-off-by: Fuqian Huang <huangfq.daxian@...il.com>
>>> ---
>>>    sound/ppc/pmac.c | 1 -
>>>    1 file changed, 1 deletion(-)
>>>
>>> diff --git a/sound/ppc/pmac.c b/sound/ppc/pmac.c
>>> index 1b11e53f6a62..1ab12f4f8631 100644
>>> --- a/sound/ppc/pmac.c
>>> +++ b/sound/ppc/pmac.c
>>> @@ -56,7 +56,6 @@ static int snd_pmac_dbdma_alloc(struct snd_pmac *chip, struct pmac_dbdma *rec, i
>>>        if (rec->space == NULL)
>>>                return -ENOMEM;
>>>        rec->size = size;
>>> -     memset(rec->space, 0, rsize);
>>>        rec->cmds = (void __iomem *)DBDMA_ALIGN(rec->space);
>>>        rec->addr = rec->dma_base + (unsigned long)((char *)rec->cmds - (char *)rec->space);
>>>
>>>