diff mbox series

[v2,5/7] hwrng: exynos: Add SMC based TRNG operation

Message ID 20240618204523.9563-6-semen.protsenko@linaro.org (mailing list archive)
State New
Headers show
Series hwrng: exynos: Add support for Exynos850 | expand

Commit Message

Sam Protsenko June 18, 2024, 8:45 p.m. UTC 
On some Exynos chips like Exynos850 the access to Security Sub System
(SSS) registers is protected with TrustZone, and therefore only possible
from EL3 monitor software. The Linux kernel is running in EL1, so the
only way for the driver to obtain TRNG data is via SMC calls to EL3
monitor. Implement such SMC operation and use it when EXYNOS_SMC flag is
set in the corresponding chip driver data.

Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
---
Changes in v2:
  - Used the "reversed Christmas tree" style in the variable declaration
    block in exynos_trng_do_read_smc()
  - Renamed .quirks to .flags in the driver structure
  - Added Krzysztof's R-b tag

 drivers/char/hw_random/exynos-trng.c | 133 +++++++++++++++++++++++++--
 1 file changed, 123 insertions(+), 10 deletions(-)

Comments

Lukasz Stelmach June 20, 2024, 1:46 p.m. UTC | #1 
It was <2024-06-18 wto 15:45>, when Sam Protsenko wrote:
> On some Exynos chips like Exynos850 the access to Security Sub System
> (SSS) registers is protected with TrustZone, and therefore only possible
> from EL3 monitor software. The Linux kernel is running in EL1, so the
> only way for the driver to obtain TRNG data is via SMC calls to EL3
> monitor. Implement such SMC operation and use it when EXYNOS_SMC flag is
> set in the corresponding chip driver data.
>
> Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
> Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> ---
> Changes in v2:
>   - Used the "reversed Christmas tree" style in the variable declaration
>     block in exynos_trng_do_read_smc()
>   - Renamed .quirks to .flags in the driver structure
>   - Added Krzysztof's R-b tag
>
>  drivers/char/hw_random/exynos-trng.c | 133 +++++++++++++++++++++++++--
>  1 file changed, 123 insertions(+), 10 deletions(-)
>
> diff --git a/drivers/char/hw_random/exynos-trng.c b/drivers/char/hw_random/exynos-trng.c
> index 99a0b271ffb7..497d6018c6ba 100644
> --- a/drivers/char/hw_random/exynos-trng.c
> +++ b/drivers/char/hw_random/exynos-trng.c
> @@ -10,6 +10,7 @@
>   * Krzysztof Kozłowski <krzk@kernel.org>
>   */

[...]

> +static int exynos_trng_init_smc(struct hwrng *rng)
> +{
> +	struct arm_smccc_res res;
> +
> +	arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_INIT, 0, 0, 0, 0, 0, 0, &res);
> +	if (res.a0 != HWRNG_RET_OK)
> +		return -EIO;
> +
> +	return 0;
> +}
> +

Does this driver requiers some vendor-specifig bootloading code?
I am testing the code on a WinLink E850-96 board booted with the
upstream u-boot and it fails during init (res0.a is -1).

[    1.883413] exynos-trng 12081400.rng: Could not register hwrng device
[    1.893394] exynos-trng 12081400.rng: probe with driver exynos-trng failed with error -5

If an additional code outside the kernel is required for this to run,
then maybe the error message should reflect that.

Kind regards,
Sam Protsenko June 20, 2024, 9:39 p.m. UTC | #2 
On Thu, Jun 20, 2024 at 8:46 AM Lukasz Stelmach <l.stelmach@samsung.com> wrote:
>
> It was <2024-06-18 wto 15:45>, when Sam Protsenko wrote:
> > On some Exynos chips like Exynos850 the access to Security Sub System
> > (SSS) registers is protected with TrustZone, and therefore only possible
> > from EL3 monitor software. The Linux kernel is running in EL1, so the
> > only way for the driver to obtain TRNG data is via SMC calls to EL3
> > monitor. Implement such SMC operation and use it when EXYNOS_SMC flag is
> > set in the corresponding chip driver data.
> >
> > Signed-off-by: Sam Protsenko <semen.protsenko@linaro.org>
> > Reviewed-by: Krzysztof Kozlowski <krzysztof.kozlowski@linaro.org>
> > ---
> > Changes in v2:
> >   - Used the "reversed Christmas tree" style in the variable declaration
> >     block in exynos_trng_do_read_smc()
> >   - Renamed .quirks to .flags in the driver structure
> >   - Added Krzysztof's R-b tag
> >
> >  drivers/char/hw_random/exynos-trng.c | 133 +++++++++++++++++++++++++--
> >  1 file changed, 123 insertions(+), 10 deletions(-)
> >
> > diff --git a/drivers/char/hw_random/exynos-trng.c b/drivers/char/hw_random/exynos-trng.c
> > index 99a0b271ffb7..497d6018c6ba 100644
> > --- a/drivers/char/hw_random/exynos-trng.c
> > +++ b/drivers/char/hw_random/exynos-trng.c
> > @@ -10,6 +10,7 @@
> >   * Krzysztof Kozłowski <krzk@kernel.org>
> >   */
>
> [...]
>
> > +static int exynos_trng_init_smc(struct hwrng *rng)
> > +{
> > +     struct arm_smccc_res res;
> > +
> > +     arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_INIT, 0, 0, 0, 0, 0, 0, &res);
> > +     if (res.a0 != HWRNG_RET_OK)
> > +             return -EIO;
> > +
> > +     return 0;
> > +}
> > +
>
> Does this driver requiers some vendor-specifig bootloading code?
> I am testing the code on a WinLink E850-96 board booted with the
> upstream u-boot and it fails during init (res0.a is -1).
>

This series was only tested (and works fine) with LittleKernel based
bootloader [1]. It's officially recommended and the only feature
complete bootloader at the moment. And you are right, the reason why
TRNG probe fails when you boot the kernel from U-Boot is that the LDFW
(Loadable Firmware) loading is not implemented in U-Boot right now,
which makes HWRNG_INIT SMC command fail and return -1. In fact, I'm
adding LDFW loading in U-Boot right now and expect it to be ready in 1
week or so. For now, can you please check with LK [1] instead? I'm
happy to help if you have any related questions.

> [    1.883413] exynos-trng 12081400.rng: Could not register hwrng device
> [    1.893394] exynos-trng 12081400.rng: probe with driver exynos-trng failed with error -5
>
> If an additional code outside the kernel is required for this to run,
> then maybe the error message should reflect that.
>

Good idea! Will send v3 soon, with proper error message added.

Thanks!

[1] https://gitlab.com/Linaro/96boards/e850-96/lk

> Kind regards,
> --
> Łukasz Stelmach
> Samsung R&D Institute Poland
> Samsung Electronics
diff mbox series

Patch

diff --git a/drivers/char/hw_random/exynos-trng.c b/drivers/char/hw_random/exynos-trng.c
index 99a0b271ffb7..497d6018c6ba 100644
--- a/drivers/char/hw_random/exynos-trng.c
+++ b/drivers/char/hw_random/exynos-trng.c
@@ -10,6 +10,7 @@ 
  * Krzysztof Kozłowski <krzk@kernel.org>
  */
 
+#include <linux/arm-smccc.h>
 #include <linux/clk.h>
 #include <linux/crypto.h>
 #include <linux/delay.h>
@@ -22,6 +23,7 @@ 
 #include <linux/mod_devicetable.h>
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
+#include <linux/property.h>
 
 #define EXYNOS_TRNG_CLKDIV		0x0
 
@@ -44,16 +46,41 @@ 
 #define EXYNOS_TRNG_FIFO_LEN		8
 #define EXYNOS_TRNG_CLOCK_RATE		500000
 
+/* Driver feature flags */
+#define EXYNOS_SMC			BIT(0)
+
+#define EXYNOS_SMC_CALL_VAL(func_num)			\
+	ARM_SMCCC_CALL_VAL(ARM_SMCCC_FAST_CALL,		\
+			   ARM_SMCCC_SMC_32,		\
+			   ARM_SMCCC_OWNER_SIP,		\
+			   func_num)
+
+/* SMC command for DTRNG access */
+#define SMC_CMD_RANDOM			EXYNOS_SMC_CALL_VAL(0x1012)
+
+/* SMC_CMD_RANDOM: arguments */
+#define HWRNG_INIT			0x0
+#define HWRNG_EXIT			0x1
+#define HWRNG_GET_DATA			0x2
+#define HWRNG_RESUME			0x3
+
+/* SMC_CMD_RANDOM: return values */
+#define HWRNG_RET_OK			0x0
+#define HWRNG_RET_RETRY_ERROR		0x2
+
+#define HWRNG_MAX_TRIES			100
+
 struct exynos_trng_dev {
 	struct device	*dev;
 	void __iomem	*mem;
 	struct clk	*clk;	/* operating clock */
 	struct clk	*pclk;	/* bus clock */
 	struct hwrng	rng;
+	unsigned long	flags;
 };
 
-static int exynos_trng_do_read(struct hwrng *rng, void *data, size_t max,
-			       bool wait)
+static int exynos_trng_do_read_reg(struct hwrng *rng, void *data, size_t max,
+				   bool wait)
 {
 	struct exynos_trng_dev *trng = (struct exynos_trng_dev *)rng->priv;
 	int val;
@@ -70,7 +97,40 @@  static int exynos_trng_do_read(struct hwrng *rng, void *data, size_t max,
 	return max;
 }
 
-static int exynos_trng_init(struct hwrng *rng)
+static int exynos_trng_do_read_smc(struct hwrng *rng, void *data, size_t max,
+				   bool wait)
+{
+	struct arm_smccc_res res;
+	unsigned int copied = 0;
+	u32 *buf = data;
+	int tries = 0;
+
+	while (copied < max) {
+		arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_GET_DATA, 0, 0, 0, 0, 0, 0,
+			      &res);
+		switch (res.a0) {
+		case HWRNG_RET_OK:
+			*buf++ = res.a2;
+			*buf++ = res.a3;
+			copied += 8;
+			tries = 0;
+			break;
+		case HWRNG_RET_RETRY_ERROR:
+			if (!wait)
+				return copied;
+			if (++tries >= HWRNG_MAX_TRIES)
+				return copied;
+			cond_resched();
+			break;
+		default:
+			return -EIO;
+		}
+	}
+
+	return copied;
+}
+
+static int exynos_trng_init_reg(struct hwrng *rng)
 {
 	struct exynos_trng_dev *trng = (struct exynos_trng_dev *)rng->priv;
 	unsigned long sss_rate;
@@ -103,6 +163,17 @@  static int exynos_trng_init(struct hwrng *rng)
 	return 0;
 }
 
+static int exynos_trng_init_smc(struct hwrng *rng)
+{
+	struct arm_smccc_res res;
+
+	arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_INIT, 0, 0, 0, 0, 0, 0, &res);
+	if (res.a0 != HWRNG_RET_OK)
+		return -EIO;
+
+	return 0;
+}
+
 static int exynos_trng_probe(struct platform_device *pdev)
 {
 	struct exynos_trng_dev *trng;
@@ -112,21 +183,29 @@  static int exynos_trng_probe(struct platform_device *pdev)
 	if (!trng)
 		return ret;
 
+	platform_set_drvdata(pdev, trng);
+	trng->dev = &pdev->dev;
+
+	trng->flags = (unsigned long)device_get_match_data(&pdev->dev);
+
 	trng->rng.name = devm_kstrdup(&pdev->dev, dev_name(&pdev->dev),
 				      GFP_KERNEL);
 	if (!trng->rng.name)
 		return ret;
 
-	trng->rng.init = exynos_trng_init;
-	trng->rng.read = exynos_trng_do_read;
 	trng->rng.priv = (unsigned long)trng;
 
-	platform_set_drvdata(pdev, trng);
-	trng->dev = &pdev->dev;
+	if (trng->flags & EXYNOS_SMC) {
+		trng->rng.init = exynos_trng_init_smc;
+		trng->rng.read = exynos_trng_do_read_smc;
+	} else {
+		trng->rng.init = exynos_trng_init_reg;
+		trng->rng.read = exynos_trng_do_read_reg;
 
-	trng->mem = devm_platform_ioremap_resource(pdev, 0);
-	if (IS_ERR(trng->mem))
-		return PTR_ERR(trng->mem);
+		trng->mem = devm_platform_ioremap_resource(pdev, 0);
+		if (IS_ERR(trng->mem))
+			return PTR_ERR(trng->mem);
+	}
 
 	pm_runtime_enable(&pdev->dev);
 	ret = pm_runtime_resume_and_get(&pdev->dev);
@@ -170,12 +249,31 @@  static int exynos_trng_probe(struct platform_device *pdev)
 
 static void exynos_trng_remove(struct platform_device *pdev)
 {
+	struct exynos_trng_dev *trng = platform_get_drvdata(pdev);
+
+	if (trng->flags & EXYNOS_SMC) {
+		struct arm_smccc_res res;
+
+		arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_EXIT, 0, 0, 0, 0, 0, 0,
+			      &res);
+	}
+
 	pm_runtime_put_sync(&pdev->dev);
 	pm_runtime_disable(&pdev->dev);
 }
 
 static int exynos_trng_suspend(struct device *dev)
 {
+	struct exynos_trng_dev *trng = dev_get_drvdata(dev);
+	struct arm_smccc_res res;
+
+	if (trng->flags & EXYNOS_SMC) {
+		arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_EXIT, 0, 0, 0, 0, 0, 0,
+			      &res);
+		if (res.a0 != HWRNG_RET_OK)
+			return -EIO;
+	}
+
 	pm_runtime_put_sync(dev);
 
 	return 0;
@@ -183,6 +281,7 @@  static int exynos_trng_suspend(struct device *dev)
 
 static int exynos_trng_resume(struct device *dev)
 {
+	struct exynos_trng_dev *trng = dev_get_drvdata(dev);
 	int ret;
 
 	ret = pm_runtime_resume_and_get(dev);
@@ -191,6 +290,20 @@  static int exynos_trng_resume(struct device *dev)
 		return ret;
 	}
 
+	if (trng->flags & EXYNOS_SMC) {
+		struct arm_smccc_res res;
+
+		arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_RESUME, 0, 0, 0, 0, 0, 0,
+			      &res);
+		if (res.a0 != HWRNG_RET_OK)
+			return -EIO;
+
+		arm_smccc_smc(SMC_CMD_RANDOM, HWRNG_INIT, 0, 0, 0, 0, 0, 0,
+			      &res);
+		if (res.a0 != HWRNG_RET_OK)
+			return -EIO;
+	}
+
 	return 0;
 }