target/linux/mvebu/patches-4.4/124-phy-improve-safety-of-fixed-phy-MII-register-reading.patch

   1 From c36739c3cfd277a4cc9820a29dd0f4b7fbac795b Mon Sep 17 00:00:00 2001
   2 From: Russell King <rmk+kernel@arm.linux.org.uk>
   3 Date: Sun, 20 Sep 2015 18:31:36 +0100
   4 Subject: [PATCH 713/744] phy: improve safety of fixed-phy MII register reading
   5
   6 There is no prevention of a concurrent call to both fixed_mdio_read()
   7 and fixed_phy_update_state(), which can result in the state being
   8 modified while it's being inspected.  Fix this by using a seqcount
   9 to detect modifications, and memcpy()ing the state.
  10
  11 We remain slightly naughty here, calling link_update() and updating
  12 the link status within the read-side loop - which would need rework
  13 of the design to change.
  14
  15 Reviewed-by: Florian Fainelli <f.fainelli@gmail.com>
  16 Signed-off-by: Russell King <rmk+kernel@arm.linux.org.uk>
  17 ---
  18  drivers/net/phy/fixed_phy.c | 28 +++++++++++++++++++++-------
  19  1 file changed, 21 insertions(+), 7 deletions(-)
  20
  21 --- a/drivers/net/phy/fixed_phy.c
  22 +++ b/drivers/net/phy/fixed_phy.c
  23 @@ -23,6 +23,7 @@
  24  #include <linux/slab.h>
  25  #include <linux/of.h>
  26  #include <linux/gpio.h>
  27 +#include <linux/seqlock.h>
  28
  29  #include "swphy.h"
  30
  31 @@ -35,6 +36,7 @@ struct fixed_mdio_bus {
  32  struct fixed_phy {
  33         int addr;
  34         struct phy_device *phydev;
  35 +       seqcount_t seqcount;
  36         struct fixed_phy_status status;
  37         int (*link_update)(struct net_device *, struct fixed_phy_status *);
  38         struct list_head node;
  39 @@ -59,13 +61,21 @@ static int fixed_mdio_read(struct mii_bu
  40
  41         list_for_each_entry(fp, &fmb->phys, node) {
  42                 if (fp->addr == phy_addr) {
  43 -                       /* Issue callback if user registered it. */
  44 -                       if (fp->link_update) {
  45 -                               fp->link_update(fp->phydev->attached_dev,
  46 -                                               &fp->status);
  47 -                               fixed_phy_update(fp);
  48 -                       }
  49 -                       return swphy_read_reg(reg_num, &fp->status);
  50 +                       struct fixed_phy_status state;
  51 +                       int s;
  52 +
  53 +                       do {
  54 +                               s = read_seqcount_begin(&fp->seqcount);
  55 +                               /* Issue callback if user registered it. */
  56 +                               if (fp->link_update) {
  57 +                                       fp->link_update(fp->phydev->attached_dev,
  58 +                                                       &fp->status);
  59 +                                       fixed_phy_update(fp);
  60 +                               }
  61 +                               state = fp->status;
  62 +                       } while (read_seqcount_retry(&fp->seqcount, s));
  63 +
  64 +                       return swphy_read_reg(reg_num, &state);
  65                 }
  66         }
  67
  68 @@ -117,6 +127,7 @@ int fixed_phy_update_state(struct phy_de
  69
  70         list_for_each_entry(fp, &fmb->phys, node) {
  71                 if (fp->addr == phydev->addr) {
  72 +                       write_seqcount_begin(&fp->seqcount);
  73  #define _UPD(x) if (changed->x) \
  74         fp->status.x = status->x
  75                         _UPD(link);
  76 @@ -126,6 +137,7 @@ int fixed_phy_update_state(struct phy_de
  77                         _UPD(asym_pause);
  78  #undef _UPD
  79                         fixed_phy_update(fp);
  80 +                       write_seqcount_end(&fp->seqcount);
  81                         return 0;
  82                 }
  83         }
  84 @@ -150,6 +162,8 @@ int fixed_phy_add(unsigned int irq, int
  85         if (!fp)
  86                 return -ENOMEM;
  87
  88 +       seqcount_init(&fp->seqcount);
  89 +
  90         fmb->irqs[phy_addr] = irq;
  91
  92         fp->addr = phy_addr;