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hwrng: bcm2835 - sleep more intelligently

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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>
This commit is contained in:
Phil Elwell
2023-03-22 15:30:38 +00:00
committed by Dom Cobley
parent b9b42dbcb5
commit 2a4f658b71
1 changed files with 14 additions and 6 deletions
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20
drivers/char/hw_random/bcm2835-rng.c
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@@ -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 bcm2835_rng_priv *priv, u32 val,
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);