target/linux/bcm27xx/patches-6.1/950-0606-hwrng-bcm2835-sleep-more-intelligently.patch

   1 From 3537a855e3858b1f8b6cee545a22b8b67037235c Mon Sep 17 00:00:00 2001
   2 From: Phil Elwell <phil@raspberrypi.com>
   3 Date: Wed, 22 Mar 2023 15:30:38 +0000
   4 Subject: [PATCH] hwrng: bcm2835 - sleep more intelligently
   5
   6 While waiting for random data, use sleeps that are proportional
   7 to the amount of data expected. Prevent indefinite waits by
   8 giving up if nothing is received for a second.
   9
  10 See: https://github.com/raspberrypi/linux/issues/5390
  11
  12 Signed-off-by: Phil Elwell <phil@raspberrypi.com>
  13 ---
  14  drivers/char/hw_random/bcm2835-rng.c | 20 ++++++++++++++------
  15  1 file changed, 14 insertions(+), 6 deletions(-)
  16
  17 --- a/drivers/char/hw_random/bcm2835-rng.c
  18 +++ b/drivers/char/hw_random/bcm2835-rng.c
  19 @@ -14,6 +14,7 @@
  20  #include <linux/printk.h>
  21  #include <linux/clk.h>
  22  #include <linux/reset.h>
  23 +#include <linux/delay.h>
  24
  25  #define RNG_CTRL       0x0
  26  #define RNG_STATUS     0x4
  27 @@ -28,6 +29,9 @@
  28
  29  #define RNG_INT_OFF    0x1
  30
  31 +#define RNG_FIFO_WORDS 4
  32 +#define RNG_US_PER_WORD        34 /* Tuned for throughput */
  33 +
  34  struct bcm2835_rng_priv {
  35         struct hwrng rng;
  36         void __iomem *base;
  37 @@ -64,19 +68,23 @@ static inline void rng_writel(struct bcm
  38  static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max,
  39                                bool wait)
  40  {
  41 +       u32 retries = 1000000/(RNG_FIFO_WORDS * RNG_US_PER_WORD);
  42         struct bcm2835_rng_priv *priv = to_rng_priv(rng);
  43         u32 max_words = max / sizeof(u32);
  44         u32 num_words, count;
  45
  46 -       while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) {
  47 -               if (!wait)
  48 +       num_words = rng_readl(priv, RNG_STATUS) >> 24;
  49 +
  50 +       while (!num_words) {
  51 +               if (!wait || !retries)
  52                         return 0;
  53 -               hwrng_yield(rng);
  54 +               retries--;
  55 +               usleep_range((u32)RNG_US_PER_WORD,
  56 +                               (u32)RNG_US_PER_WORD * RNG_FIFO_WORDS);
  57 +               num_words = rng_readl(priv, RNG_STATUS) >> 24;
  58         }
  59
  60 -       num_words = rng_readl(priv, RNG_STATUS) >> 24;
  61 -       if (num_words > max_words)
  62 -               num_words = max_words;
  63 +       num_words = min(num_words, max_words);
  64
  65         for (count = 0; count < num_words; count++)
  66                 ((u32 *)buf)[count] = rng_readl(priv, RNG_DATA);