linux-kernel - Re: [PATCH] hwrng: bcm2835: set quality to 1000

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Message-ID: <YDFeao/bOxvoXI9D@lunn.ch>
Date:   Sat, 20 Feb 2021 20:09:30 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Álvaro Fernández Rojas <noltari@...il.com>
Cc:     mpm@...enic.com, herbert@...dor.apana.org.au,
        nsaenzjulienne@...e.de, f.fainelli@...il.com, rjui@...adcom.com,
        sbranden@...adcom.com, bcm-kernel-feedback-list@...adcom.com,
        rikard.falkeborn@...il.com, linux-crypto@...r.kernel.org,
        linux-rpi-kernel@...ts.infradead.org,
        linux-arm-kernel@...ts.infradead.org, linux-kernel@...r.kernel.org,
        stijn@...ux-ipv6.be, ynezz@...e.cz
Subject: Re: [PATCH] hwrng: bcm2835: set quality to 1000

On Sat, Feb 20, 2021 at 06:47:40PM +0100, Álvaro Fernández Rojas wrote:
> This allows devices without a high precission timer to reduce boot from >100s
> to <30s.
> diff --git a/drivers/char/hw_random/bcm2835-rng.c b/drivers/char/hw_random/bcm2835-rng.c
> index 1a7c43b43c6b..4b48cb7176b0 100644
> --- a/drivers/char/hw_random/bcm2835-rng.c
> +++ b/drivers/char/hw_random/bcm2835-rng.c
> @@ -163,6 +163,7 @@ static int bcm2835_rng_probe(struct platform_device *pdev)
>  	priv->rng.init = bcm2835_rng_init;
>  	priv->rng.read = bcm2835_rng_read;
>  	priv->rng.cleanup = bcm2835_rng_cleanup;
> +	priv->rng.quality = 1000;

Hi Alvero

 * @quality:		Estimation of true entropy in RNG's bitstream
 *			(in bits of entropy per 1024 bits of input;
 *			valid values: 1 to 1024, or 0 for unknown).

How did you determine this device produces 1000 bits of true entropy
per 1024?

    Andrew