linux-kernel - [RFC PATCH v1 26/50] drivers/nfc/nfcsim: use prandom

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Message-Id: <202003281643.02SGhHox023138@sdf.org>
Date:   Wed, 20 Mar 2019 22:50:00 -0400
From:   George Spelvin <lkml@....org>
To:     linux-kernel@...r.kernel.org, lkml@....org
Cc:     Thierry Escande <thierry.escande@...labora.com>,
        Samuel Ortiz <sameo@...ux.intel.com>, linux-nfc@...ts.01.org
Subject: [RFC PATCH v1 26/50] drivers/nfc/nfcsim: use prandom_32() for time
 delay

get_random_bytes() is expensive crypto-quality seed material.
That's not needed for a simple simulation.

(Also, a 3-10 ms delay, when converted to jiffies, isn't a lot of
granularity.  It's 1 jiffy at HZ=100 and 3 jiffies at HZ=250
or HZ=300.)

Signed-off-by: George Spelvin <lkml@....org>
Cc: Thierry Escande <thierry.escande@...labora.com>
Cc: Samuel Ortiz <sameo@...ux.intel.com>
Cc: linux-nfc@...ts.01.org
---
 drivers/nfc/nfcsim.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/drivers/nfc/nfcsim.c b/drivers/nfc/nfcsim.c
index a9864fcdfba6b..eb0a909a25487 100644
--- a/drivers/nfc/nfcsim.c
+++ b/drivers/nfc/nfcsim.c
@@ -229,8 +229,7 @@ static int nfcsim_send(struct nfc_digital_dev *ddev, struct sk_buff *skb,
 				    dev->mode);
 
 		/* Add random delay (between 3 and 10 ms) before sending data */
-		get_random_bytes(&delay, 1);
-		delay = 3 + (delay & 0x07);
+		delay = 3 + prandom_u32_max(8);
 
 		schedule_delayed_work(&dev->send_work, msecs_to_jiffies(delay));
 	}
-- 
2.26.0