[PATCH v5 3/8] stm32mp1: rng: Add a driver for random number generator(rng) device
Heinrich Schuchardt
xypron.glpk at gmx.de
Fri Dec 27 13:42:11 CET 2019
On 12/27/19 12:19 PM, Sughosh Ganu wrote:
>
> On Fri, 27 Dec 2019 at 13:21, Heinrich Schuchardt <xypron.glpk at gmx.de
> <mailto:xypron.glpk at gmx.de>> wrote:
>
> On 12/26/19 6:25 PM, Sughosh Ganu wrote:
> > Add a driver for the rng device found on stm32mp1 platforms. The
> > driver provides a routine for reading the random number seed from the
> > hardware device.
> >
> > Signed-off-by: Sughosh Ganu <sughosh.ganu at linaro.org
> <mailto:sughosh.ganu at linaro.org>>
> > Reviewed-by: Patrice Chotard <patrice.chotard at st.com
> <mailto:patrice.chotard at st.com>>
> > Acked-by: Patrick Delaunay <patrick.delaunay at st.com
> <mailto:patrick.delaunay at st.com>>
> > ---
> > Changes since V4:
> > * Return number of bytes read on a successful read, and a -ve
> value on
> > error.
> >
> > drivers/rng/Kconfig | 7 ++
> > drivers/rng/Makefile | 1 +
> > drivers/rng/stm32mp1_rng.c | 165
> +++++++++++++++++++++++++++++++++++++++++++++
> > 3 files changed, 173 insertions(+)
> > create mode 100644 drivers/rng/stm32mp1_rng.c
> >
> > diff --git a/drivers/rng/Kconfig b/drivers/rng/Kconfig
> > index dd44cc0..c9c4751 100644
> > --- a/drivers/rng/Kconfig
> > +++ b/drivers/rng/Kconfig
> > @@ -5,3 +5,10 @@ config DM_RNG
> > Enable driver model for random number generator(rng) devices.
> > This interface is used to initialise the rng device and to
> > read the random seed from the device.
> > +
> > +config RNG_STM32MP1
> > + bool "Enable random number generator for STM32MP1"
> > + depends on ARCH_STM32MP && DM_RNG
> > + default n
> > + help
> > + Enable STM32MP1 rng driver.
> > diff --git a/drivers/rng/Makefile b/drivers/rng/Makefile
> > index 311705b..699beb3 100644
> > --- a/drivers/rng/Makefile
> > +++ b/drivers/rng/Makefile
> > @@ -4,3 +4,4 @@
> > #
> >
> > obj-$(CONFIG_DM_RNG) += rng-uclass.o
> > +obj-$(CONFIG_RNG_STM32MP1) += stm32mp1_rng.o
> > diff --git a/drivers/rng/stm32mp1_rng.c b/drivers/rng/stm32mp1_rng.c
> > new file mode 100644
> > index 0000000..56ad848
> > --- /dev/null
> > +++ b/drivers/rng/stm32mp1_rng.c
> > @@ -0,0 +1,165 @@
> > +// SPDX-License-Identifier: GPL-2.0-or-later
> > +/*
> > + * Copyright (c) 2019, Linaro Limited
> > + */
> > +
> > +#include <common.h>
> > +#include <clk.h>
> > +#include <dm.h>
> > +#include <reset.h>
> > +#include <rng.h>
> > +
> > +#include <asm/io.h>
> > +#include <linux/iopoll.h>
> > +#include <linux/kernel.h>
> > +
> > +#define RNG_CR 0x00
> > +#define RNG_CR_RNGEN BIT(2)
> > +#define RNG_CR_CED BIT(5)
> > +
> > +#define RNG_SR 0x04
> > +#define RNG_SR_SEIS BIT(6)
> > +#define RNG_SR_CEIS BIT(5)
> > +#define RNG_SR_SECS BIT(2)
> > +#define RNG_SR_DRDY BIT(0)
> > +
> > +#define RNG_DR 0x08
> > +
> > +struct stm32_rng_platdata {
> > + fdt_addr_t base;
> > + struct clk clk;
> > + struct reset_ctl rst;
> > +};
> > +
> > +static int stm32_rng_read(struct udevice *dev, void *data,
> size_t len)
> > +{
> > + int retval = 0, i, nbytes;
> > + u32 sr, count, reg;
> > + size_t increment;
> > + struct stm32_rng_platdata *pdata = dev_get_platdata(dev);
> > +
> > + /*
> > + * Only INT_MAX number of bytes can be returned. If more
> > + * bytes need to be read, the caller must do it in a loop.
> > + */
> > + if (len > INT_MAX)
> > + len = INT_MAX;
> > +
> > + nbytes = len;
> > + while (len > 0) {
> > + retval = readl_poll_timeout(pdata->base + RNG_SR, sr,
> > + sr & RNG_SR_DRDY, 10000);
> > + if (retval)
> > + return retval;
> > +
> > + if (sr & (RNG_SR_SEIS | RNG_SR_SECS)) {
> > + /* As per SoC TRM */
> > + clrbits_le32(pdata->base + RNG_SR,
> RNG_SR_SEIS);
> > + for (i = 0; i < 12; i++)
> > + readl(pdata->base + RNG_DR);
> > + if (readl(pdata->base + RNG_SR) &
> RNG_SR_SEIS) {
> > + printf("RNG Noise");
> > + return -EIO;
>
> The SEIS bit indicates a seed error. According to the RM0090 Reference
> manual for the STM32F429/439 you should clear the SEIS bit and set the
> RNGEN bit to restart the RNG.
>
> https://www.st.com/content/ccc/resource/technical/document/reference_manual/3d/6d/5a/66/b4/99/40/d4/DM00031020.pdf/files/DM00031020.pdf/jcr:content/translations/en.DM00031020.pdf,
> page 768.
>
> So why do you return an error code here? What do you expect the caller
> to do?
>
>
> I am referring to the stm32mp157 trm, Noise source error detection, pg 1939.
Could you, please, provide a link to the document for stm32mp157.
compatible = "st,stm32-rng" is provided in U-Boot by:
* stm32f429.dtsi included by
stm32429i-eval.dts, arch/arm/dts/stm32f429-disco.dts, and
stm32f469-disco.dts
* as well as by stm32mp157c.dtsi included by
stm32mp157a-avenger96.dts, stm32mp157a-dk1.dts, and
stm32mp157c-ed1.dts.
So we have to consider both SoCs here.
Best regards
Heinrich
>
>
> Should we check the CEIS flag which indicates a clock error?
>
>
> The stm32mp1 clk driver in tf-a sets the rng peripheral source to
> lsi_ck, which is 32KHz. This is configured after tests done by ST
> engineers to provide better entropy. However, with this clock source,
> the CEIS bit is set, since Frng is less than (Fhclk/32). This is not an
> issue though, since the trm clearly states that the clock error has no
> impact on the generated random numbers, and that the application can
> still read the RNG_DR register.
>
>
> > + }
> > + /* start again */
> > + continue;
> > + }
> > +
>
> It took me some time to understand what this loop does. Please, add a
> comment indicating that we copy up to 16 random bytes from the RNG.
>
>
> Ok. Will do.
>
> -sughosh
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