linux-kernel - Re: [PATCH v2] scsi: libsas: Allocation SMP request is aligned to ARCH_DMA

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Message-ID: <75df3e2d-10c3-5370-3cd8-fe2fb0ff2acc@huawei.com>
Date: Thu, 28 Mar 2024 14:59:40 +0800
From: Yihang Li <liyihang9@...wei.com>
To: Christoph Hellwig <hch@...radead.org>, John Garry
	<john.g.garry@...cle.com>
CC: Damien Le Moal <dlemoal@...nel.org>, <yanaijie@...wei.com>,
	<jejb@...ux.ibm.com>, <martin.petersen@...cle.com>,
	<chenxiang66@...ilicon.com>, <linux-scsi@...r.kernel.org>,
	<linux-kernel@...r.kernel.org>, <linuxarm@...wei.com>,
	<prime.zeng@...wei.com>, <yangxingui@...wei.com>, <liyihang9@...wei.com>
Subject: Re: [PATCH v2] scsi: libsas: Allocation SMP request is aligned to
 ARCH_DMA_MINALIGN



On 2024/3/28 14:35, Christoph Hellwig wrote:
> On Tue, Mar 26, 2024 at 01:32:09PM +0000, John Garry wrote:
>>>> +	u8 *p;
>>>> +
>>>> +	size = ALIGN(size, ARCH_DMA_MINALIGN);
>>
>>
>> If this is a hisi_sas requirement, then why use ARCH_DMA_MINALIGN and not
>> 16B as minimum alignment?
>>
>> Or are we really talking about an arch requirement?
> 
> One thing is that we should never allocate unaligned memory for
> anything DMA mapped, or data will be corrupted by non-coherent DMA.
> So ARCH_DMA_MINALIGN needs to be here.  If specific hardware has
> further requirements we'll need to communicated it through a field
> or op vector.

Got it. Looks like it's still going to be aligned to ARCH_DMA_MINALIGN.

Thanks,
Yihang

> 
> 
> .
>