linux-kernel - Re: [PATCH 3/3] hwrng: msm

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Date:   Mon, 18 Jun 2018 11:21:23 -0700
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Vinod Koul <vinod.koul@...aro.org>
Cc:     linux-crypto@...r.kernel.org, linux-kernel@...r.kernel.org,
        Matt Mackall <mpm@...enic.com>,
        Herbert Xu <herbert@...dor.apana.org.au>,
        Arnd Bergmann <arnd@...db.de>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        linux-arm-msm@...r.kernel.org, Vinod Koul <vkoul@...nel.org>
Subject: Re: [PATCH 3/3] hwrng: msm - Add support for prng v2

On Mon 18 Jun 07:12 PDT 2018, Vinod Koul wrote:

> Qcom 8996 and later chips support prng v2 where we need to only
> implement .read callback for hwrng.
> 

The hardware still needs initialization, so I think you should expand
this to mention that the initialization is moved to secure world and
that's the reason why we only implement read.

The question is what happens in projects with other security models.

> Add a new table for v2 which supports this and get version required for
> driver data.
> 
> Signed-off-by: Vinod Koul <vkoul@...nel.org>
> ---
>  drivers/char/hw_random/msm-rng.c | 13 ++++++++++++-
>  1 file changed, 12 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/char/hw_random/msm-rng.c b/drivers/char/hw_random/msm-rng.c
> index 7644474035e5..3f509072a6c6 100644
> --- a/drivers/char/hw_random/msm-rng.c
> +++ b/drivers/char/hw_random/msm-rng.c
> @@ -17,6 +17,7 @@
>  #include <linux/io.h>
>  #include <linux/module.h>
>  #include <linux/of.h>
> +#include <linux/of_device.h>
>  #include <linux/platform_device.h>
>  
>  /* Device specific register offsets */
> @@ -132,10 +133,16 @@ static struct hwrng msm_rng = {
>  	.read = msm_rng_read,
>  };
>  
> +static struct hwrng msm_rng_v2 = {
> +	.name = KBUILD_MODNAME,
> +	.read = msm_rng_read,
> +};
> +
>  static int msm_rng_probe(struct platform_device *pdev)
>  {
>  	struct resource *res;
>  	struct msm_rng *rng;
> +	unsigned int version;
>  	int ret;
>  
>  	rng = devm_kzalloc(&pdev->dev, sizeof(*rng), GFP_KERNEL);
> @@ -154,6 +161,9 @@ static int msm_rng_probe(struct platform_device *pdev)
>  		return PTR_ERR(rng->clk);
>  
>  	rng->hwrng = &msm_rng;
> +	version = (unsigned long)of_device_get_match_data(&pdev->dev);

If this is "version" then please make it 1 or 2, if you agree with
Stephen's suggestion of omitting the initialization of init I think this
would be better as 0/1 and the variable named "skip_init".

> +	if (version)
> +		rng->hwrng = &msm_rng_v2;
>  
>  	rng->hwrng->priv = (unsigned long)rng;
>  	ret = devm_hwrng_register(&pdev->dev, rng->hwrng);
> @@ -166,7 +176,8 @@ static int msm_rng_probe(struct platform_device *pdev)
>  }
>  
>  static const struct of_device_id msm_rng_of_match[] = {
> -	{ .compatible = "qcom,prng", },
> +	{ .compatible = "qcom,prng", .data = (void *)0},
> +	{ .compatible = "qcom,prng-v2", .data = (void *)1},
>  	{}
>  };
>  MODULE_DEVICE_TABLE(of, msm_rng_of_match);

Regards,
Bjorn