linux-kernel - Re: [PATCH] ocxl: Add get_metadata IOCTL to share OCXL information to userspace

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Date:   Thu, 22 Feb 2018 10:37:43 +1100
From:   "Alastair D'Silva" <alastair@....ibm.com>
To:     Frederic Barrat <fbarrat@...ux.vnet.ibm.com>,
        Balbir Singh <bsingharora@...il.com>
Cc:     Arnd Bergmann <arnd@...db.de>, frederic.barrat@...ibm.com,
        Greg KH <gregkh@...uxfoundation.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...abs.org>,
        Andrew Donnellan <andrew.donnellan@....ibm.com>
Subject: Re: [PATCH] ocxl: Add get_metadata IOCTL to share OCXL information
 to userspace

On Wed, 2018-02-21 at 12:25 +0100, Frederic Barrat wrote:
> 
> Le 21/02/2018 à 07:43, Balbir Singh a écrit :
> > On Wed, Feb 21, 2018 at 3:57 PM, Alastair D'Silva <alastair@....ibm
> > .com> wrote:
> > > From: Alastair D'Silva <alastair@...ilva.org>
> > > 
> > > Some required information is not exposed to userspace currently
> > > (eg. the
> > > PASID), pass this information back, along with other information
> > > which
> > > is currently communicated via sysfs, which saves some parsing
> > > effort in
> > > userspace.
> > > 
> > > Signed-off-by: Alastair D'Silva <alastair@...ilva.org>
> > > 
<snip>
> > Should we document the fields? pp_ stands for per process, but is
> > not
> > very clear at first look. Why do we care to return only the size,
> > what
> > about lpc size?
> 
> My bad, I forgot to mention it before. There's a somewhat high-level 
> description which needs updating in:
> Documentation/accelerators/ocxl.rst
> 
> It doesn't go down to the level of the structure members, but at
> least 
> all ioctl commands should have a brief description.
> 

I'll update the docs.

> lpc_size could be added. It's currently useless to the library, but 
> doesn't hurt. The one which was giving me troubles on a previous
> version 
> of this patch was the lpc numa node ID, since that was experimental
> code 
> and felt out of place considering what's been upstreamed in skiboot
> and 
> linux so far.

I'd rather add the LPC members when the rest of the LPC code goes in.
At the moment, the LPC size represents the window size (as a power of
2), whereas we expect that it should represent the actual amount of LPC
memory exposed. I would rather avoid changing semantics of members in
released code, or burning another reserved member for the updated
definition if we can avoid it.

-- 
Alastair D'Silva
Open Source Developer
Linux Technology Centre, IBM Australia
mob: 0423 762 819