linux-kernel - Re: [PATCH v2 1/1] powerpc/iommu: Enable remaining IOMMU Pagesizes present in LoPAR

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Message-ID: <fd20f4fae3d4bc1de0e62a25cead4db00bdd8dbd.camel@gmail.com>
Date:   Wed, 14 Apr 2021 01:02:16 -0300
From:   Leonardo Bras <leobras.c@...il.com>
To:     Segher Boessenkool <segher@...nel.crashing.org>,
        Alexey Kardashevskiy <aik@...abs.ru>
Cc:     Michael Ellerman <mpe@...erman.id.au>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Paul Mackerras <paulus@...ba.org>, brking@...ux.vnet.ibm.com,
        linuxppc-dev@...ts.ozlabs.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2 1/1] powerpc/iommu: Enable remaining IOMMU Pagesizes
 present in LoPAR

On Mon, 2021-04-12 at 17:21 -0500, Segher Boessenkool wrote:
> On Fri, Apr 09, 2021 at 02:36:16PM +1000, Alexey Kardashevskiy wrote:
> > On 08/04/2021 19:04, Michael Ellerman wrote:
> > > > > > +#define QUERY_DDW_PGSIZE_4K	0x01
> > > > > > +#define QUERY_DDW_PGSIZE_64K	0x02
> > > > > > +#define QUERY_DDW_PGSIZE_16M	0x04
> > > > > > +#define QUERY_DDW_PGSIZE_32M	0x08
> > > > > > +#define QUERY_DDW_PGSIZE_64M	0x10
> > > > > > +#define QUERY_DDW_PGSIZE_128M	0x20
> > > > > > +#define QUERY_DDW_PGSIZE_256M	0x40
> > > > > > +#define QUERY_DDW_PGSIZE_16G	0x80
> > > > > 
> > > > > I'm not sure the #defines really gain us much vs just putting the
> > > > > literal values in the array below?
> > > > 
> > > > Then someone says "uuuuu magic values" :) I do not mind either way. 
> > > > Thanks,
> > > 
> > > Yeah that's true. But #defining them doesn't make them less magic, if
> > > you only use them in one place :)
> > 
> > Defining them with "QUERY_DDW" in the names kinda tells where they are 
> > from. Can also grep QEMU using these to see how the other side handles 
> > it. Dunno.
> 
> And *not* defining anything reduces the mental load a lot.  You can add
> a comment at the single spot you use them, explaining what this is, in a
> much better way!
> 
> Comments are *good*.
> 
> 
> Segher

Thanks for the feedback Alexey, Michael and Segher!

I have sent a v3 for this patch. 
http://patchwork.ozlabs.org/project/linuxppc-dev/patch/20210408201915.174217-1-leobras.c@gmail.com/

Please let me know of your feedback in it.

Best regards,
Leonardo Bras