linux-kernel - Re: [PATCH] ath9k: use hw_random API instead of directly dumping into random.c

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Date:   Wed, 16 Feb 2022 00:22:00 +0100
From:   Toke Høiland-Jørgensen <toke@...e.dk>
To:     "Jason A. Donenfeld" <Jason@...c4.com>, miaoqing@...eaurora.org,
        Jason Cooper <jason@...edaemon.net>,
        "Sepehrdad, Pouyan" <pouyans@....qualcomm.com>,
        ath9k-devel <ath9k-devel@....qualcomm.com>,
        "linux-wireless@...r.kernel.org" <linux-wireless@...r.kernel.org>,
        Kalle Valo <kvalo@...nel.org>,
        Dominik Brodowski <linux@...inikbrodowski.net>,
        Linux Crypto Mailing List <linux-crypto@...r.kernel.org>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        LKML <linux-kernel@...r.kernel.org>,
        Netdev <netdev@...r.kernel.org>
Subject: Re: [PATCH] ath9k: use hw_random API instead of directly dumping
 into random.c

"Jason A. Donenfeld" <Jason@...c4.com> writes:

> Hardware random number generators are supposed to use the hw_random
> framework. This commit turns ath9k's kthread-based design into a proper
> hw_random driver.
>
> This compiles, but I have no hardware or other ability to determine
> whether it works. I'll leave further development up to the ath9k
> and hw_random maintainers.
>
> Cc: Toke Høiland-Jørgensen <toke@...hat.com>
> Cc: Kalle Valo <kvalo@...nel.org>
> Cc: Dominik Brodowski <linux@...inikbrodowski.net>
> Cc: Herbert Xu <herbert@...dor.apana.org.au>
> Signed-off-by: Jason A. Donenfeld <Jason@...c4.com>
> ---
>  drivers/net/wireless/ath/ath9k/ath9k.h |  2 +-
>  drivers/net/wireless/ath/ath9k/rng.c   | 62 +++++++++-----------------
>  2 files changed, 23 insertions(+), 41 deletions(-)
>
> diff --git a/drivers/net/wireless/ath/ath9k/ath9k.h b/drivers/net/wireless/ath/ath9k/ath9k.h
> index ef6f5ea06c1f..142f472903dc 100644
> --- a/drivers/net/wireless/ath/ath9k/ath9k.h
> +++ b/drivers/net/wireless/ath/ath9k/ath9k.h
> @@ -1072,7 +1072,7 @@ struct ath_softc {
>  
>  #ifdef CONFIG_ATH9K_HWRNG
>  	u32 rng_last;
> -	struct task_struct *rng_task;
> +	struct hwrng rng_ops;
>  #endif
>  };
>  
> diff --git a/drivers/net/wireless/ath/ath9k/rng.c b/drivers/net/wireless/ath/ath9k/rng.c
> index aae2bd3cac69..369b222908ba 100644
> --- a/drivers/net/wireless/ath/ath9k/rng.c
> +++ b/drivers/net/wireless/ath/ath9k/rng.c
> @@ -22,9 +22,6 @@
>  #include "hw.h"
>  #include "ar9003_phy.h"
>  
> -#define ATH9K_RNG_BUF_SIZE	320
> -#define ATH9K_RNG_ENTROPY(x)	(((x) * 8 * 10) >> 5) /* quality: 10/32 */

So this comment says "quality: 10/32" but below you're setting "quality"
as 320. No idea what the units are supposed to be, but is this right?

>  static DECLARE_WAIT_QUEUE_HEAD(rng_queue);
>  
>  static int ath9k_rng_data_read(struct ath_softc *sc, u32 *buf, u32 buf_size)

This function takes buf as a *u32, and interprets buf_size as a number
of u32s...

> @@ -72,61 +69,46 @@ static u32 ath9k_rng_delay_get(u32 fail_stats)
>  	return delay;
>  }
>  
> -static int ath9k_rng_kthread(void *data)
> +static int ath9k_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
>  {
> +	struct ath_softc *sc = container_of(rng, struct ath_softc, rng_ops);
>  	int bytes_read;
> -	struct ath_softc *sc = data;
> -	u32 *rng_buf;
> -	u32 delay, fail_stats = 0;
> -
> -	rng_buf = kmalloc_array(ATH9K_RNG_BUF_SIZE, sizeof(u32), GFP_KERNEL);
> -	if (!rng_buf)
> -		goto out;
> -
> -	while (!kthread_should_stop()) {
> -		bytes_read = ath9k_rng_data_read(sc, rng_buf,
> -						 ATH9K_RNG_BUF_SIZE);
> -		if (unlikely(!bytes_read)) {
> -			delay = ath9k_rng_delay_get(++fail_stats);
> -			wait_event_interruptible_timeout(rng_queue,
> -							 kthread_should_stop(),
> -							 msecs_to_jiffies(delay));
> -			continue;
> -		}
> -
> -		fail_stats = 0;
> -
> -		/* sleep until entropy bits under write_wakeup_threshold */
> -		add_hwgenerator_randomness((void *)rng_buf, bytes_read,
> -					   ATH9K_RNG_ENTROPY(bytes_read));
> -	}
> +	u32 fail_stats = 0;
>  
> -	kfree(rng_buf);
> -out:
> -	sc->rng_task = NULL;
> +retry:
> +	bytes_read = ath9k_rng_data_read(sc, buf, max);

... but AFAICT here you're calling it with a buffer size from hw_random
that's in bytes?

-Toke