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From c4d2d5e97430599f16255695b9f4be4381542992 Mon Sep 17 00:00:00 2001
From: Phil Elwell <phil@raspberrypi.com>
Date: Wed, 22 Mar 2023 15:30:38 +0000
Subject: [PATCH 0962/1085] hwrng: bcm2835 - sleep more intelligently
While waiting for random data, use sleeps that are proportional
to the amount of data expected. Prevent indefinite waits by
giving up if nothing is received for a second.
See: https://github.com/raspberrypi/linux/issues/5390
Signed-off-by: Phil Elwell <phil@raspberrypi.com>
---
drivers/char/hw_random/bcm2835-rng.c | 20 ++++++++++++++------
1 file changed, 14 insertions(+), 6 deletions(-)
--- a/drivers/char/hw_random/bcm2835-rng.c
+++ b/drivers/char/hw_random/bcm2835-rng.c
@@ -13,6 +13,7 @@
#include <linux/printk.h>
#include <linux/clk.h>
#include <linux/reset.h>
+#include <linux/delay.h>
#define RNG_CTRL 0x0
#define RNG_STATUS 0x4
@@ -27,6 +28,9 @@
#define RNG_INT_OFF 0x1
+#define RNG_FIFO_WORDS 4
+#define RNG_US_PER_WORD 34 /* Tuned for throughput */
+
struct bcm2835_rng_priv {
struct hwrng rng;
void __iomem *base;
@@ -63,19 +67,23 @@ static inline void rng_writel(struct bcm
static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max,
bool wait)
{
+ u32 retries = 1000000/(RNG_FIFO_WORDS * RNG_US_PER_WORD);
struct bcm2835_rng_priv *priv = to_rng_priv(rng);
u32 max_words = max / sizeof(u32);
u32 num_words, count;
- while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) {
- if (!wait)
+ num_words = rng_readl(priv, RNG_STATUS) >> 24;
+
+ while (!num_words) {
+ if (!wait || !retries)
return 0;
- hwrng_yield(rng);
+ retries--;
+ usleep_range((u32)RNG_US_PER_WORD,
+ (u32)RNG_US_PER_WORD * RNG_FIFO_WORDS);
+ num_words = rng_readl(priv, RNG_STATUS) >> 24;
}
- num_words = rng_readl(priv, RNG_STATUS) >> 24;
- if (num_words > max_words)
- num_words = max_words;
+ num_words = min(num_words, max_words);
for (count = 0; count < num_words; count++)
((u32 *)buf)[count] = rng_readl(priv, RNG_DATA);
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