linux-kernel - [PATCH] dmaengine: rcar-dmac: Rename highmem/lowmem

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Date:	Thu, 14 Jan 2016 18:59:33 +0900
From:	Magnus Damm <magnus.damm@...il.com>
To:	linux-kernel@...r.kernel.org
Cc:	laurent.pinchart+renesas@...asonboard.com, geert+renesas@...der.be,
	linux-sh@...r.kernel.org, vinod.koul@...el.com,
	dmaengine@...r.kernel.org, horms+renesas@...ge.net.au,
	Magnus Damm <magnus.damm@...il.com>
Subject: [PATCH] dmaengine: rcar-dmac: Rename highmem/lowmem

From: Magnus Damm <damm+renesas@...nsource.se>

Update the rcar-dmac driver to rework comments and variable names
related to lowmem and highmem.

Terminology such as highmem and lowmem are commonly used for Linux
kernel memory managment. Highmem in particular is about handling more
physical memory than can fit into the kernel virtual address space.

Highmem and lowmem are related to but not equivalent to the 40-bit
address limitation that is the real issue the rcar-dmac driver has to
deal with. For instance, with 1 GiB of RAM highmem is usually needed
on a 32-bit architecture, but a 32-bit address is still enough.

64-bit architectures tend to not use highmem since the virtual
address space is more than enough for loads of lowmem. 32-bit
architectures may still need highmem to access all memory.

The rcar-dmac driver and the DMA device needs to handle the 40-bit
limitation on both 64-bit and 32-bit architectures.

This patch renames the highmem variable to fourty_bit_required to
avoid confusion. And the comment gets updated as well.

Signed-off-by: Magnus Damm <damm+renesas@...nsource.se>
---

 drivers/dma/sh/rcar-dmac.c |   12 ++++++------
 1 file changed, 6 insertions(+), 6 deletions(-)

--- 0001/drivers/dma/sh/rcar-dmac.c
+++ work/drivers/dma/sh/rcar-dmac.c	2016-01-14 18:35:23.780513000 +0900
@@ -889,7 +889,7 @@ rcar_dmac_chan_prep_sg(struct rcar_dmac_
 	unsigned int nchunks = 0;
 	unsigned int max_chunk_size;
 	unsigned int full_size = 0;
-	bool highmem = false;
+	bool fourty_bit_required = false;
 	unsigned int i;

 	desc = rcar_dmac_desc_get(chan);
@@ -935,7 +935,7 @@ rcar_dmac_chan_prep_sg(struct rcar_dmac_
 			 * hardware descriptor lists.
 			 */
 			if (dev_addr >> 32 || mem_addr >> 32)
-				highmem = true;
+				fourty_bit_required = true;
 #endif

 			chunk = rcar_dmac_xfer_chunk_get(chan);
@@ -977,13 +977,13 @@ rcar_dmac_chan_prep_sg(struct rcar_dmac_
 	 * Use hardware descriptor lists if possible when more than one chunk
 	 * needs to be transferred (otherwise they don't make much sense).
 	 *
-	 * The highmem check currently covers the whole transfer. As an
-	 * optimization we could use descriptor lists for consecutive lowmem
-	 * chunks and direct manual mode for highmem chunks. Whether the
+	 * The 40-bit address check currently covers the whole transfer. As an
+	 * optimization we could use descriptor lists for consecutive 32-bit
+	 * chunks and direct manual mode for 40-bit chunks. Whether the
 	 * performance improvement would be significant enough compared to the
 	 * additional complexity remains to be investigated.
 	 */
-	desc->hwdescs.use = !highmem && nchunks > 1;
+	desc->hwdescs.use = !fourty_bit_required && nchunks > 1;
 	if (desc->hwdescs.use) {
 		if (rcar_dmac_fill_hwdesc(chan, desc) < 0)
 			desc->hwdescs.use = false;