Re: [PATCH 3/3] hwrng: add mt67xx-rng driver

[Neal Liu <neal.liu@mediatek.com>]

Hi Stephan,
	We think the cast is fine, and it cannot guarantee the buf is
word-align.
	I reference multiple rng driver's implementation and found it's common
usage for this. So it might be general usage for community. Is there any
suggestion that is more appropriate?

	Thanks
Best Regards,
-Neal Liu


On Wed, 2019-05-08 at 08:34 +0200, Stephan Mueller wrote:
> Am Mittwoch, 8. Mai 2019, 05:58:57 CEST schrieb neal.liu@mediatek.com:
> 
> Hi liu,
> 
> > From: Neal Liu <neal.liu@mediatek.com>
> > 
> > For Mediatek SoCs on ARMv8 with TrustZone enabled, peripherals like
> > entropy sources is not accessible from normal world (linux) and
> > rather accessible from secure world (ATF/TEE) only. This driver aims
> > to provide a generic interface to ATF rng service.
> > 
> > Signed-off-by: Neal Liu <neal.liu@mediatek.com>
> > ---
> >  drivers/char/hw_random/Kconfig      |   16 ++++++
> >  drivers/char/hw_random/Makefile     |    1 +
> >  drivers/char/hw_random/mt67xx-rng.c |  104
> > +++++++++++++++++++++++++++++++++++ 3 files changed, 121 insertions(+)
> >  create mode 100644 drivers/char/hw_random/mt67xx-rng.c
> > 
> > diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
> > index 25a7d8f..98751d3 100644
> > --- a/drivers/char/hw_random/Kconfig
> > +++ b/drivers/char/hw_random/Kconfig
> > @@ -398,6 +398,22 @@ config HW_RANDOM_MTK
> > 
> >  	  If unsure, say Y.
> > 
> > +config HW_RANDOM_MT67XX
> > +	tristate "Mediatek MT67XX Random Number Generator support"
> > +	depends on HW_RANDOM
> > +	depends on ARCH_MEDIATEK || COMPILE_TEST
> > +	default HW_RANDOM
> > +	help
> > +	  This driver provides kernel-side support for the Random Number
> > +	  Generator hardware found on Mediatek MT67xx SoCs. The difference
> > +	  with mtk-rng is the Random Number Generator hardware is secure
> > +	  access only.
> > +
> > +	  To compile this driver as a module, choose M here. the
> > +	  module will be called mt67xx-rng.
> > +
> > +	  If unsure, say Y.
> > +
> >  config HW_RANDOM_S390
> >  	tristate "S390 True Random Number Generator support"
> >  	depends on S390
> > diff --git a/drivers/char/hw_random/Makefile
> > b/drivers/char/hw_random/Makefile index 7c9ef4a..4be95ab 100644
> > --- a/drivers/char/hw_random/Makefile
> > +++ b/drivers/char/hw_random/Makefile
> > @@ -36,6 +36,7 @@ obj-$(CONFIG_HW_RANDOM_PIC32) += pic32-rng.o
> >  obj-$(CONFIG_HW_RANDOM_MESON) += meson-rng.o
> >  obj-$(CONFIG_HW_RANDOM_CAVIUM) += cavium-rng.o cavium-rng-vf.o
> >  obj-$(CONFIG_HW_RANDOM_MTK)	+= mtk-rng.o
> > +obj-$(CONFIG_HW_RANDOM_MT67XX) += mt67xx-rng.o
> >  obj-$(CONFIG_HW_RANDOM_S390) += s390-trng.o
> >  obj-$(CONFIG_HW_RANDOM_KEYSTONE) += ks-sa-rng.o
> >  obj-$(CONFIG_HW_RANDOM_OPTEE) += optee-rng.o
> > diff --git a/drivers/char/hw_random/mt67xx-rng.c
> > b/drivers/char/hw_random/mt67xx-rng.c new file mode 100644
> > index 0000000..e70cbbe
> > --- /dev/null
> > +++ b/drivers/char/hw_random/mt67xx-rng.c
> > @@ -0,0 +1,104 @@
> > +// SPDX-License-Identifier: GPL-2.0
> > +/*
> > + * Copyright (C) 2019 MediaTek Inc.
> > + */
> > +
> > +#include <linux/module.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/hw_random.h>
> > +#include <linux/of.h>
> > +#include <linux/arm-smccc.h>
> > +#include <linux/soc/mediatek/mtk_sip_svc.h>
> > +
> > +#define PFX			KBUILD_MODNAME ": "
> > +#define MT67XX_RNG_MAGIC	0x74726e67
> > +#define SMC_RET_NUM		4
> > +
> > +struct mt67xx_rng_priv {
> > +	struct hwrng rng;
> > +};
> > +
> > +
> > +static void __rng_sec_read(uint32_t *val)
> > +{
> > +	struct arm_smccc_res res;
> > +
> > +	arm_smccc_smc(MTK_SIP_KERNEL_GET_RND,
> > +		      MT67XX_RNG_MAGIC, 0, 0, 0, 0, 0, 0, &res);
> > +
> > +	val[0] = res.a0;
> > +	val[1] = res.a1;
> > +	val[2] = res.a2;
> > +	val[3] = res.a3;
> > +}
> > +
> > +static int mt67xx_rng_read(struct hwrng *rng, void *buf, size_t max, bool
> > wait) +{
> > +	int i, retval = 0;
> > +	uint32_t val[4] = {0};
> > +	size_t get_rnd_size = sizeof(u32) * SMC_RET_NUM;
> > +
> > +	if (!buf) {
> > +		pr_err("%s, buf is NULL\n", __func__);
> > +		return -EFAULT;
> > +	}
> > +
> > +	while (max >= get_rnd_size) {
> > +		__rng_sec_read(val);
> > +
> > +		for (i = 0; i < SMC_RET_NUM; i++) {
> > +			*(u32 *)buf = val[i];
> 
> I am not sure this cast is right - or how is it guaranteed that buf is word-
> aligned?
> 
> > +			buf += sizeof(u32);
> > +		}
> > +
> > +		retval += get_rnd_size;
> > +		max -= get_rnd_size;
> > +	}
> > +
> > +	return retval;
> > +}
> > +
> > +static int mt67xx_rng_probe(struct platform_device *pdev)
> > +{
> > +	int ret;
> > +	struct mt67xx_rng_priv *priv;
> > +
> > +	pr_info(PFX "driver registered\n");
> > +	priv = devm_kzalloc(&pdev->dev, sizeof(*priv), GFP_KERNEL);
> > +	if (!priv)
> > +		return -ENOMEM;
> > +
> > +	priv->rng.name = KBUILD_MODNAME;
> > +	priv->rng.read = mt67xx_rng_read;
> > +	priv->rng.priv = (unsigned long)&pdev->dev;
> > +	priv->rng.quality = 900;
> > +
> > +	ret = devm_hwrng_register(&pdev->dev, &priv->rng);
> > +	if (ret) {
> > +		dev_err(&pdev->dev, "failed to register rng device: %d\n", 
> ret);
> > +		return ret;
> > +	}
> > +
> > +	return 0;
> > +}
> > +
> > +static const struct of_device_id mt67xx_rng_match[] = {
> > +	{ .compatible = "mediatek,mt67xx-rng", },
> > +	{}
> > +};
> > +MODULE_DEVICE_TABLE(of, mt67xx_rng_match);
> > +
> > +static struct platform_driver mt67xx_rng_driver = {
> > +	.probe = mt67xx_rng_probe,
> > +	.driver = {
> > +		.name = KBUILD_MODNAME,
> > +		.owner = THIS_MODULE,
> > +		.of_match_table = mt67xx_rng_match,
> > +	},
> > +};
> > +
> > +module_platform_driver(mt67xx_rng_driver);
> > +
> > +MODULE_DESCRIPTION("Mediatek MT67XX Random Number Generator Driver");
> > +MODULE_AUTHOR("Neal Liu <neal.liu@mediatek.com>");
> > +MODULE_LICENSE("GPL");
> 
> 
> 
> Ciao
> Stephan
> 
>