target/linux/bcm27xx/patches-5.4/950-0448-mm-refresh-ZONE_DMA-and-ZONE_DMA32-comments-in-enum-.patch

   1 From 1c108eaeae73a504ac1b2d882bc1fefb91eecf17 Mon Sep 17 00:00:00 2001
   2 From: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
   3 Date: Wed, 11 Sep 2019 20:25:46 +0200
   4 Subject: [PATCH] mm: refresh ZONE_DMA and ZONE_DMA32 comments in 'enum
   5  zone_type'
   6
   7 commit 734f9246e791d8da278957b2c326d7709b2a97c0 upstream.
   8
   9 These zones usage has evolved with time and the comments were outdated.
  10 This joins both ZONE_DMA and ZONE_DMA32 explanation and gives up to date
  11 examples on how they are used on different architectures.
  12
  13 Signed-off-by: Nicolas Saenz Julienne <nsaenzjulienne@suse.de>
  14 Reviewed-by: Christoph Hellwig <hch@lst.de>
  15 Reviewed-by: Catalin Marinas <catalin.marinas@arm.com>
  16 Signed-off-by: Catalin Marinas <catalin.marinas@arm.com>
  17 ---
  18  include/linux/mmzone.h | 45 ++++++++++++++++++++++++------------------
  19  1 file changed, 26 insertions(+), 19 deletions(-)
  20
  21 --- a/include/linux/mmzone.h
  22 +++ b/include/linux/mmzone.h
  23 @@ -358,33 +358,40 @@ struct per_cpu_nodestat {
  24  #endif /* !__GENERATING_BOUNDS.H */
  25
  26  enum zone_type {
  27 -#ifdef CONFIG_ZONE_DMA
  28         /*
  29 -        * ZONE_DMA is used when there are devices that are not able
  30 -        * to do DMA to all of addressable memory (ZONE_NORMAL). Then we
  31 -        * carve out the portion of memory that is needed for these devices.
  32 -        * The range is arch specific.
  33 -        *
  34 -        * Some examples
  35 -        *
  36 -        * Architecture         Limit
  37 -        * ---------------------------
  38 -        * parisc, ia64, sparc  <4G
  39 -        * s390, powerpc        <2G
  40 -        * arm                  Various
  41 -        * alpha                Unlimited or 0-16MB.
  42 +        * ZONE_DMA and ZONE_DMA32 are used when there are peripherals not able
  43 +        * to DMA to all of the addressable memory (ZONE_NORMAL).
  44 +        * On architectures where this area covers the whole 32 bit address
  45 +        * space ZONE_DMA32 is used. ZONE_DMA is left for the ones with smaller
  46 +        * DMA addressing constraints. This distinction is important as a 32bit
  47 +        * DMA mask is assumed when ZONE_DMA32 is defined. Some 64-bit
  48 +        * platforms may need both zones as they support peripherals with
  49 +        * different DMA addressing limitations.
  50 +        *
  51 +        * Some examples:
  52 +        *
  53 +        *  - i386 and x86_64 have a fixed 16M ZONE_DMA and ZONE_DMA32 for the
  54 +        *    rest of the lower 4G.
  55 +        *
  56 +        *  - arm only uses ZONE_DMA, the size, up to 4G, may vary depending on
  57 +        *    the specific device.
  58 +        *
  59 +        *  - arm64 has a fixed 1G ZONE_DMA and ZONE_DMA32 for the rest of the
  60 +        *    lower 4G.
  61 +        *
  62 +        *  - powerpc only uses ZONE_DMA, the size, up to 2G, may vary
  63 +        *    depending on the specific device.
  64          *
  65 -        * i386, x86_64 and multiple other arches
  66 -        *                      <16M.
  67 +        *  - s390 uses ZONE_DMA fixed to the lower 2G.
  68 +        *
  69 +        *  - ia64 and riscv only use ZONE_DMA32.
  70 +        *
  71 +        *  - parisc uses neither.
  72          */
  73 +#ifdef CONFIG_ZONE_DMA
  74         ZONE_DMA,
  75  #endif
  76  #ifdef CONFIG_ZONE_DMA32
  77 -       /*
  78 -        * x86_64 needs two ZONE_DMAs because it supports devices that are
  79 -        * only able to do DMA to the lower 16M but also 32 bit devices that
  80 -        * can only do DMA areas below 4G.
  81 -        */
  82         ZONE_DMA32,
  83  #endif
  84         /*