67 lines
1.9 KiB
Diff
67 lines
1.9 KiB
Diff
From 3537a855e3858b1f8b6cee545a22b8b67037235c Mon Sep 17 00:00:00 2001
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From: Phil Elwell <phil@raspberrypi.com>
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Date: Wed, 22 Mar 2023 15:30:38 +0000
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Subject: [PATCH] hwrng: bcm2835 - sleep more intelligently
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While waiting for random data, use sleeps that are proportional
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to the amount of data expected. Prevent indefinite waits by
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giving up if nothing is received for a second.
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See: https://github.com/raspberrypi/linux/issues/5390
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Signed-off-by: Phil Elwell <phil@raspberrypi.com>
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---
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drivers/char/hw_random/bcm2835-rng.c | 20 ++++++++++++++------
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1 file changed, 14 insertions(+), 6 deletions(-)
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--- a/drivers/char/hw_random/bcm2835-rng.c
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+++ b/drivers/char/hw_random/bcm2835-rng.c
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@@ -14,6 +14,7 @@
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#include <linux/printk.h>
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#include <linux/clk.h>
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#include <linux/reset.h>
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+#include <linux/delay.h>
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#define RNG_CTRL 0x0
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#define RNG_STATUS 0x4
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@@ -28,6 +29,9 @@
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#define RNG_INT_OFF 0x1
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+#define RNG_FIFO_WORDS 4
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+#define RNG_US_PER_WORD 34 /* Tuned for throughput */
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+
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struct bcm2835_rng_priv {
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struct hwrng rng;
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void __iomem *base;
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@@ -64,19 +68,23 @@ static inline void rng_writel(struct bcm
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static int bcm2835_rng_read(struct hwrng *rng, void *buf, size_t max,
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bool wait)
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{
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+ u32 retries = 1000000/(RNG_FIFO_WORDS * RNG_US_PER_WORD);
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struct bcm2835_rng_priv *priv = to_rng_priv(rng);
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u32 max_words = max / sizeof(u32);
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u32 num_words, count;
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- while ((rng_readl(priv, RNG_STATUS) >> 24) == 0) {
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- if (!wait)
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+ num_words = rng_readl(priv, RNG_STATUS) >> 24;
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+
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+ while (!num_words) {
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+ if (!wait || !retries)
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return 0;
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- hwrng_yield(rng);
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+ retries--;
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+ usleep_range((u32)RNG_US_PER_WORD,
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+ (u32)RNG_US_PER_WORD * RNG_FIFO_WORDS);
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+ num_words = rng_readl(priv, RNG_STATUS) >> 24;
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}
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- num_words = rng_readl(priv, RNG_STATUS) >> 24;
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- if (num_words > max_words)
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- num_words = max_words;
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+ num_words = min(num_words, max_words);
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for (count = 0; count < num_words; count++)
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((u32 *)buf)[count] = rng_readl(priv, RNG_DATA);
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