linux-kernel - Re: [PATCH 4/4 v4] iommu/fsl: Freescale PAMU driver and IOMMU API implementation.

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Date:	Mon, 5 Nov 2012 17:11:15 -0600
From:	Scott Wood <scottwood@...escale.com>
To:	Timur Tabi <timur@...escale.com>
CC:	Varun Sethi <Varun.Sethi@...escale.com>, <joerg.roedel@....com>,
	<iommu@...ts.linux-foundation.org>,
	<linuxppc-dev@...ts.ozlabs.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH 4/4 v4] iommu/fsl: Freescale PAMU driver and IOMMU API
 implementation.

On 11/05/2012 05:04:13 PM, Timur Tabi wrote:
> Varun Sethi wrote:
> > +	/* PAACE Offset 0x00 */
> > +	u32 wbah;				/* only valid for  
> Primary PAACE */
> > +	u32 addr_bitfields;		/* See P/S PAACE_AF_* */
> > +
> > +	/* PAACE Offset 0x08 */
> > +	/* Interpretation of first 32 bits dependent on DD above */
> > +	union {
> > +		struct {
> > +			/* Destination ID, see PAACE_DID_* defines */
> > +			u8 did;
> > +			/* Partition ID */
> > +			u8 pid;
> > +			/* Snoop ID */
> > +			u8 snpid;
> > +			/* coherency_required : 1 reserved : 7 */
> 
> Please use this format, which is easier to read:
> 
> 			/* 1 == coherency required, 7 == reserved */
> 
> Every time I look at this comment, I think you are using bitfields.

It is meant as a pseudo-bitfield.  "7 == reserved" doesn't make much  
sense -- that would leave a lot of other values neither defined nor  
explicitly reserved.

That said, the "See PAACE_DA_*" comment should be sufficient and avoids  
making people have to care about what bitfield ordering the comment  
writer was assuming.

-Scott
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