linux-kernel - Re: [PATCH 1/2] hwrng: iproc-rng200: Fix disable of the block.

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Date:   Mon, 14 Dec 2020 09:45:37 -0800
From:   Scott Branden <scott.branden@...adcom.com>
To:     matthias.bgg@...nel.org, mpm@...enic.com,
        herbert@...dor.apana.org.au, rjui@...adcom.com,
        sbranden@...adcom.com, f.fainelli@...il.com
Cc:     linux-kernel@...r.kernel.org, Julia.Lawall@...ia.fr,
        bcm-kernel-feedback-list@...adcom.com,
        linux-arm-kernel@...ts.infradead.org, nsaenzjulienne@...e.de,
        linux-crypto@...r.kernel.org, Matthias Brugger <mbrugger@...e.com>
Subject: Re: [PATCH 1/2] hwrng: iproc-rng200: Fix disable of the block.



On 2020-12-14 8:04 a.m., matthias.bgg@...nel.org wrote:
> From: Matthias Brugger <mbrugger@...e.com>
>
> When trying to disable the block we bitwise or the control
> register with value zero. This will leave the block always turned on.
> Fix this by setting the corresponding bit to zero.
>
> Fixes: c83d45d5685f ("hwrng: iproc-rng200 - Add Broadcom IPROC RNG driver")
Commit message needs to be re-written.
I don't think this is an actual fix as the ~RNG_CTL_RNG_RBGEN_MASK already zeros the bit.  This is just a code change, which is fine because it makes things clearer
> Signed-off-by: Matthias Brugger <mbrugger@...e.com>
> ---
>
>  drivers/char/hw_random/iproc-rng200.c | 5 ++---
>  1 file changed, 2 insertions(+), 3 deletions(-)
>
> diff --git a/drivers/char/hw_random/iproc-rng200.c b/drivers/char/hw_random/iproc-rng200.c
> index 01583faf9893..e106ce3c0146 100644
> --- a/drivers/char/hw_random/iproc-rng200.c
> +++ b/drivers/char/hw_random/iproc-rng200.c
> @@ -28,7 +28,6 @@
>  #define RNG_CTRL_OFFSET					0x00
>  #define RNG_CTRL_RNG_RBGEN_MASK				0x00001FFF
>  #define RNG_CTRL_RNG_RBGEN_ENABLE			0x00000001
> -#define RNG_CTRL_RNG_RBGEN_DISABLE			0x00000000
>  
>  #define RNG_SOFT_RESET_OFFSET				0x04
>  #define RNG_SOFT_RESET					0x00000001
> @@ -61,7 +60,7 @@ static void iproc_rng200_restart(void __iomem *rng_base)
>  	/* Disable RBG */
>  	val = ioread32(rng_base + RNG_CTRL_OFFSET);
>  	val &= ~RNG_CTRL_RNG_RBGEN_MASK;
This mask will already zero the enable bit.
> -	val |= RNG_CTRL_RNG_RBGEN_DISABLE;
> +	val &= ~RNG_CTRL_RNG_RBGEN_ENABLE;
>  	iowrite32(val, rng_base + RNG_CTRL_OFFSET);
>  
>  	/* Clear all interrupt status */
> @@ -174,7 +173,7 @@ static void iproc_rng200_cleanup(struct hwrng *rng)
>  	/* Disable RNG hardware */
>  	val = ioread32(priv->base + RNG_CTRL_OFFSET);
>  	val &= ~RNG_CTRL_RNG_RBGEN_MASK;
> -	val |= RNG_CTRL_RNG_RBGEN_DISABLE;
> +	val &= ~RNG_CTRL_RNG_RBGEN_ENABLE;
>  	iowrite32(val, priv->base + RNG_CTRL_OFFSET);
>  }
>