On Mon, Dec 01, 2014 at 01:33:09PM +0000, Laurent Pinchart wrote:

On Monday 01 December 2014 12:13:38 Will Deacon wrote:

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On Sun, Nov 30, 2014 at 10:00:21PM +0000, Laurent Pinchart wrote:

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On Thursday 27 November 2014 11:51:15 Will Deacon wrote:

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diff --git a/drivers/iommu/io-pgtable.c b/drivers/iommu/io-pgtable.c
new file mode 100644
index 000000000000..82e39a0db94b
--- /dev/null
+++ b/drivers/iommu/io-pgtable.c

@@ -0,0 +1,71 @@
+/*
+ * Generic page table allocator for IOMMUs.
+ *
+ * This program is free software; you can redistribute it and/or modify
+ * it under the terms of the GNU General Public License version 2 as
+ * published by the Free Software Foundation.
+ *
+ * This program is distributed in the hope that it will be useful,
+ * but WITHOUT ANY WARRANTY; without even the implied warranty of
+ * MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the
+ * GNU General Public License for more details.
+ *
+ * You should have received a copy of the GNU General Public License
+ * along with this program; if not, write to the Free Software
+ * Foundation, Inc., 59 Temple Place - Suite 330, Boston, MA

02111-1307, USA.

By the way you can remove this paragraph, we don't want to update all source 
files the day the FSF decides to move to a new address.

Yeah, I missed that one (I fixed the lpae file already).

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diff --git a/drivers/iommu/io-pgtable.h b/drivers/iommu/io-pgtable.h
new file mode 100644
index 000000000000..5ae75d9cae50
--- /dev/null
+++ b/drivers/iommu/io-pgtable.h

@@ -0,0 +1,65 @@
+#ifndef __IO_PGTABLE_H
+#define __IO_PGTABLE_H
+
+struct io_pgtable_ops {
+	int (*map)(struct io_pgtable_ops *ops, unsigned long iova,

How about passing a struct io_pgtable * instead of the ops pointer ? This
would require returning a struct io_pgtable from the alloc function, which
I suppose you didn't want to do to ensure the caller will not touch the
struct io_pgtable fields directly. Do we really need to go that far, or
can we simply document struct io_pgtable as being private to the pg alloc
framework core and allocators ? Someone who really wants to get hold of
the io_pgtable instance could use container_of on the ops anyway, like
the allocators do.

Hmm, currently the struct io_pgtable is private to the page table allocator,
so I don't like the IOMMU driver having an explicit handle to that.

I agree with this, but given that struct io_pgtable is defined in a header 
used by the IOMMU driver, and given that it directly embeds struct 
io_pgtable_ops, there's no big difference between the two structures.

Right, but you have to do an explicit container_of and, with the kerneldoc
added, it should be clear that it's not a good idea to mess with things
like the cookie or the cfg after you've allocated the page tables.

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I also like having the value returned from alloc_io_pgtable_ops being used
as the handle to pass around -- it keeps things simple for the caller
because there's one structure that you get back and that's the thing you use
as a reference.

I agree with that as well, my proposal was to return a struct io_pgtable from 
alloc_io_pgtable_ops.

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What do we gain by returning the struct io_pgtable pointer instead?

The ops structure could be made a const pointer. That's a pretty small 
optimization, granted.

I still think I'd rather keep things like they are. Let's see how it looks
in v2, when I've reordered the structures and documented them.

Will