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

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Date: Wed, 27 Mar 2024 23:35:19 -0700
From: Christoph Hellwig <hch@...radead.org>
To: John Garry <john.g.garry@...cle.com>
Cc: Damien Le Moal <dlemoal@...nel.org>, Yihang Li <liyihang9@...wei.com>,
	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
Subject: Re: [PATCH v2] scsi: libsas: Allocation SMP request is aligned to
 ARCH_DMA_MINALIGN

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.