Re: [PATCH 4/6] hwrng: st: Add support for ST's HW Random Number Generator

[Lee Jones]

On Sat, 12 Sep 2015, Kieran Bingham wrote:
> On 11 September 2015 at 21:08, Lee Jones <lee.jones@xxxxxxxxxx> wrote:
> > Signed-off-by: Pankaj Dev <pankaj.dev@xxxxxx>
> > Signed-off-by: Lee Jones <lee.jones@xxxxxxxxxx>
> > ---
> >  drivers/char/hw_random/Kconfig  |  10 +++
> >  drivers/char/hw_random/Makefile |   1 +
> >  drivers/char/hw_random/st-rng.c | 142 ++++++++++++++++++++++++++++++++++++++++
> >  3 files changed, 153 insertions(+)
> >  create mode 100644 drivers/char/hw_random/st-rng.c
> >
> > diff --git a/drivers/char/hw_random/Kconfig b/drivers/char/hw_random/Kconfig
> > index f48cf11..bb6cb77 100644
> > --- a/drivers/char/hw_random/Kconfig
> > +++ b/drivers/char/hw_random/Kconfig
> > @@ -346,6 +346,16 @@ config HW_RANDOM_MSM
> >
> >           If unsure, say Y.
> >
> > +config HW_RANDOM_ST
> > +       tristate "ST Microelectronics HW Random Number Generator support"
> > +       depends on HW_RANDOM && ARCH_STI
> > +       ---help---
> > +         This driver provides kernel-side support for the Random Number
> > +         Generator hardware found on STi series of SoCs.
> > +
> > +         To compile this driver as a module, choose M here: the
> > +         module will be called st-rng.
> > +
> >  config HW_RANDOM_XGENE
> >         tristate "APM X-Gene True Random Number Generator (TRNG) support"
> >         depends on HW_RANDOM && ARCH_XGENE
> > diff --git a/drivers/char/hw_random/Makefile b/drivers/char/hw_random/Makefile
> > index 055bb01..8bcfb45 100644
> > --- a/drivers/char/hw_random/Makefile
> > +++ b/drivers/char/hw_random/Makefile
> > @@ -30,4 +30,5 @@ obj-$(CONFIG_HW_RANDOM_TPM) += tpm-rng.o
> >  obj-$(CONFIG_HW_RANDOM_BCM2835) += bcm2835-rng.o
> >  obj-$(CONFIG_HW_RANDOM_IPROC_RNG200) += iproc-rng200.o
> >  obj-$(CONFIG_HW_RANDOM_MSM) += msm-rng.o
> > +obj-$(CONFIG_HW_RANDOM_ST) += st-rng.o
> >  obj-$(CONFIG_HW_RANDOM_XGENE) += xgene-rng.o
> > diff --git a/drivers/char/hw_random/st-rng.c b/drivers/char/hw_random/st-rng.c
> > new file mode 100644
> > index 0000000..717a831
> > --- /dev/null
> > +++ b/drivers/char/hw_random/st-rng.c
> > @@ -0,0 +1,142 @@
> > +/*
> > + * ST Random Number Generator Driver ST's Platforms
> > + *
> > + * Author: Pankaj Dev: <pankaj.dev@xxxxxx>
> > + *         Lee Jones <lee.jones@xxxxxxxxxx>
> > + *
> > + * Copyright (C) 2015 STMicroelectronics (R&D) Limited
> > + *
> > + * This program is free software; you can redistribute it and/or modify
> > + * it under the terms of the GNU General Public License version 2 as
> > + * published by the Free Software Foundation.
> > + */
> > +
> > +#include <linux/clk.h>
> > +#include <linux/delay.h>
> > +#include <linux/hw_random.h>
> > +#include <linux/io.h>
> > +#include <linux/module.h>
> > +#include <linux/of.h>
> > +#include <linux/platform_device.h>
> > +#include <linux/slab.h>
> > +
> > +/* Registers */
> > +#define ST_RNG_STATUS_REG              0x20
> > +#define ST_RNG_DATA_REG                        0x24
> > +
> > +/* Registers fields */
> > +#define ST_RNG_STATUS_BAD_SEQUENCE     BIT(0)
> > +#define ST_RNG_STATUS_BAD_ALTERNANCE   BIT(1)
> > +#define ST_RNG_STATUS_FIFO_FULL                BIT(5)
> > +
> > +#define ST_RNG_FIFO_SIZE               8
> > +#define ST_RNG_SAMPLE_SIZE             2 /* 2 Byte (16bit) samples */
> > +
> > +/* Samples are available every 0.667us, which we round to 1us */
> > +#define ST_RNG_FILL_FIFO_TIMEOUT   (1 * (ST_RNG_FIFO_SIZE / ST_RNG_SAMPLE_SIZE))
> > +
> > +struct st_rng_data {
> > +       void __iomem    *base;
> > +       struct clk      *clk;
> > +       struct hwrng    ops;
> > +};
> > +
> > +static int st_rng_read(struct hwrng *rng, void *data, size_t max, bool wait)
> > +{
> > +       struct st_rng_data *ddata = (struct st_rng_data *)rng->priv;
> > +       u32 status;
> > +       int i;
> > +
> > +       if (max < sizeof(u16))
> > +               return -EINVAL;
> > +
> > +       /* Wait until FIFO is full - max 4uS*/
> > +       for (i = 0; i < ST_RNG_FILL_FIFO_TIMEOUT; i++) {
> > +               status = readl_relaxed(ddata->base + ST_RNG_STATUS_REG);
> > +               if (status & ST_RNG_STATUS_FIFO_FULL)
> > +                       break;
> > +               udelay(1);
> > +       }
> > +
> > +       if (i == ST_RNG_FILL_FIFO_TIMEOUT)
> > +               return 0;
> > +
> > +       for (i = 0; i < ST_RNG_FIFO_SIZE && i < max; i += 2)
> > +               *(u16 *)(data + i) =
> > +                       readl_relaxed(ddata->base + ST_RNG_DATA_REG);
> 
> Will this code always be called with max % 2 == 0? ...
>  I.e. will
>     st_rng_read(rng, data[5], 5, waitflg)
>  overflow an array?

.read() can be called with either 16, 32 or the size of the cache,
which is unlikely to be anything !(N^2) (it's 64 in our case).

> > +
> > +       return i - 2;   /* No of bytes read */
> 
>   Really? Doesn't this return 0 on st_rng_read(rng, data[2], 2, waitflg);

Hmm... I assumed the OA's math was good here.

Good spot.  I will run some tests to confirm.

> > +}
> > +
> > +static int st_rng_probe(struct platform_device *pdev)
> > +{
> > +       struct st_rng_data *ddata;
> > +       struct resource *res;
> > +       struct clk *clk;
> > +       void __iomem *base;
> > +       int ret;
> > +
> > +       ddata = devm_kzalloc(&pdev->dev, sizeof(*ddata), GFP_KERNEL);
> > +       if (!ddata)
> > +               return -ENOMEM;
> > +
> > +       res = platform_get_resource(pdev, IORESOURCE_MEM, 0);
> > +       base = devm_ioremap_resource(&pdev->dev, res);
> > +       if (IS_ERR(base))
> 
> Are we leaking ddata here ? I.e. before its attached with set_drvdata?

It won't leak.  That's the point of devm_*.

Please see: Documentation/driver-model/devres.txt

> > +               return PTR_ERR(base);
> > +
> > +       clk = devm_clk_get(&pdev->dev, NULL);
> > +       if (!clk)
> 
> And here ...

Nope.

> > +               return -EINVAL;
> > +
> > +       clk_prepare_enable(clk);
> > +
> > +       ddata->ops.priv = (unsigned long)ddata;
> > +       ddata->ops.read = st_rng_read;
> > +       ddata->ops.name = pdev->name;
> > +       ddata->base     = base;
> > +       ddata->clk      = clk;
> > +
> > +       dev_set_drvdata(&pdev->dev, ddata);
> > +
> > +       ret = hwrng_register(&ddata->ops);
> > +       if (ret) {
> > +               dev_err(&pdev->dev, "Failed to register HW RNG\n");
> > +               return ret;
> > +       }
> > +
> > +       dev_info(&pdev->dev, "Successfully registered HW RNG\n");
> > +
> > +       return 0;
> > +}
> > +
> > +static int st_rng_remove(struct platform_device *pdev)
> > +{
> > +       struct st_rng_data *ddata = dev_get_drvdata(&pdev->dev);
> > +
> > +       hwrng_unregister(&ddata->ops);
> > +
> > +       clk_disable_unprepare(ddata->clk);
> > +
> > +       return 0;
> > +}
> > +
> > +static const struct of_device_id st_rng_match[] = {
> > +       { .compatible = "st,rng" },
> > +       {},
> > +};
> > +MODULE_DEVICE_TABLE(of, st_rng_match);
> > +
> > +static struct platform_driver st_rng_driver = {
> > +       .driver = {
> > +               .name = "st-hwrandom",
> > +               .of_match_table = of_match_ptr(st_rng_match),
> > +       },
> > +       .probe = st_rng_probe,
> > +       .remove = st_rng_remove
> > +};
> > +
> > +module_platform_driver(st_rng_driver);
> > +
> > +MODULE_AUTHOR("Pankaj Dev <pankaj.dev@xxxxxx>");
> > +MODULE_LICENSE("GPL v2");
> >
> 
> 

-- 
Lee Jones
Linaro STMicroelectronics Landing Team Lead
Linaro.org â Open source software for ARM SoCs
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