[PATCH 1/2] dt-bindings: rng: mtk-rng: add SMC-based TRNG variants

[PATCH 1/2] dt-bindings: rng: mtk-rng: add SMC-based TRNG variants

[Daniel Golle]

Add compatible strings for MediaTek SoCs where the hardware random number
generator is accessed via a vendor-defined Secure Monitor Call (SMC)
rather than direct MMIO register access:

  - mediatek,mt7981-rng
  - mediatek,mt7987-rng
  - mediatek,mt7988-rng

These variants require no reg, clocks, or clock-names properties since
the RNG hardware is managed by ARM Trusted Firmware-A.

Relax the $nodename pattern to also allow 'rng' in addition to the
existing 'rng@...' pattern.

Add a second example showing the minimal SMC variant binding.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
 .../devicetree/bindings/rng/mtk-rng.yaml      | 28 ++++++++++++++++---
 1 file changed, 24 insertions(+), 4 deletions(-)

diff --git a/Documentation/devicetree/bindings/rng/mtk-rng.yaml b/Documentation/devicetree/bindings/rng/mtk-rng.yaml
index 7e8dc62e5d3a6..6074758552ac3 100644
--- a/Documentation/devicetree/bindings/rng/mtk-rng.yaml
+++ b/Documentation/devicetree/bindings/rng/mtk-rng.yaml
@@ -11,12 +11,15 @@ maintainers:
 
 properties:
   $nodename:
-    pattern: "^rng@[0-9a-f]+$"
+    pattern: "^rng(@[0-9a-f]+)?$"
 
   compatible:
     oneOf:
       - enum:
           - mediatek,mt7623-rng
+          - mediatek,mt7981-rng
+          - mediatek,mt7987-rng
+          - mediatek,mt7988-rng
       - items:
           - enum:
               - mediatek,mt7622-rng
@@ -38,9 +41,22 @@ properties:
 
 required:
   - compatible
-  - reg
-  - clocks
-  - clock-names
+
+allOf:
+  - if:
+      properties:
+        compatible:
+          not:
+            contains:
+              enum:
+                - mediatek,mt7981-rng
+                - mediatek,mt7987-rng
+                - mediatek,mt7988-rng
+    then:
+      required:
+        - reg
+        - clocks
+        - clock-names
 
 additionalProperties: false
 
@@ -53,3 +69,7 @@ examples:
             clocks = <&infracfg CLK_INFRA_TRNG>;
             clock-names = "rng";
     };
+  - |
+    rng {
+            compatible = "mediatek,mt7981-rng";
+    };
-- 
2.53.0

[PATCH 2/2] hwrng: mtk - add support for hw access via SMCC

[Daniel Golle]

Newer versions of ARM TrustedFirmware-A on MediaTek's ARMv8 SoCs no longer
allow accessing the TRNG from outside of the trusted firmware.
Instead, a vendor-defined custom Secure Monitor Call can be used to
acquire random bytes.

Add support for newer SoCs (MT7981, MT7987, MT7988).

As TF-A for the MT7986 may either follow the old or the new
convention, the best bet is to test if firmware blocks direct access
to the hwrng and if so, expect the SMCC interface to be usable.

Signed-off-by: Daniel Golle <daniel@makrotopia.org>
---
 drivers/char/hw_random/mtk-rng.c | 127 ++++++++++++++++++++++++++-----
 1 file changed, 106 insertions(+), 21 deletions(-)

diff --git a/drivers/char/hw_random/mtk-rng.c b/drivers/char/hw_random/mtk-rng.c
index 5808d09d12c45..8f5856b59ad66 100644
--- a/drivers/char/hw_random/mtk-rng.c
+++ b/drivers/char/hw_random/mtk-rng.c
@@ -3,6 +3,7 @@
  * Driver for Mediatek Hardware Random Number Generator
  *
  * Copyright (C) 2017 Sean Wang <sean.wang@mediatek.com>
+ * Copyright (C) 2026 Daniel Golle <daniel@makrotopia.org>
  */
 #define MTK_RNG_DEV KBUILD_MODNAME
 
@@ -17,6 +18,8 @@
 #include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/pm_runtime.h>
+#include <linux/arm-smccc.h>
+#include <linux/soc/mediatek/mtk_sip_svc.h>
 
 /* Runtime PM autosuspend timeout: */
 #define RNG_AUTOSUSPEND_TIMEOUT		100
@@ -30,6 +33,11 @@
 
 #define RNG_DATA			0x08
 
+/* Driver feature flags */
+#define MTK_RNG_SMC			BIT(0)
+
+#define MTK_SIP_KERNEL_GET_RND		MTK_SIP_SMC_CMD(0x550)
+
 #define to_mtk_rng(p)	container_of(p, struct mtk_rng, rng)
 
 struct mtk_rng {
@@ -37,6 +45,7 @@ struct mtk_rng {
 	struct clk *clk;
 	struct hwrng rng;
 	struct device *dev;
+	unsigned long flags;
 };
 
 static int mtk_rng_init(struct hwrng *rng)
@@ -103,6 +112,56 @@ static int mtk_rng_read(struct hwrng *rng, void *buf, size_t max, bool wait)
 	return retval || !wait ? retval : -EIO;
 }
 
+static int mtk_rng_read_smc(struct hwrng *rng, void *buf, size_t max,
+			    bool wait)
+{
+	struct arm_smccc_res res;
+	int retval = 0;
+
+	while (max >= sizeof(u32)) {
+		arm_smccc_smc(MTK_SIP_KERNEL_GET_RND, 0, 0, 0, 0, 0, 0, 0,
+			      &res);
+		if (res.a0)
+			break;
+
+		*(u32 *)buf = res.a1;
+		retval += sizeof(u32);
+		buf += sizeof(u32);
+		max -= sizeof(u32);
+	}
+
+	return retval || !wait ? retval : -EIO;
+}
+
+static bool mtk_rng_hw_accessible(struct mtk_rng *priv)
+{
+	u32 val;
+	int err;
+
+	err = clk_prepare_enable(priv->clk);
+	if (err)
+		return false;
+
+	val = readl(priv->base + RNG_CTRL);
+	val |= RNG_EN;
+	writel(val, priv->base + RNG_CTRL);
+
+	val = readl(priv->base + RNG_CTRL);
+
+	if (val & RNG_EN) {
+		/* HW is accessible, clean up: disable RNG and clock */
+		writel(val & ~RNG_EN, priv->base + RNG_CTRL);
+		clk_disable_unprepare(priv->clk);
+		return true;
+	}
+
+	/*
+	 * If TF-A blocks direct access, the register reads back as 0.
+	 * Leave the clock enabled as TF-A needs it.
+	 */
+	return false;
+}
+
 static int mtk_rng_probe(struct platform_device *pdev)
 {
 	int ret;
@@ -114,23 +173,42 @@ static int mtk_rng_probe(struct platform_device *pdev)
 
 	priv->dev = &pdev->dev;
 	priv->rng.name = pdev->name;
-#ifndef CONFIG_PM
-	priv->rng.init = mtk_rng_init;
-	priv->rng.cleanup = mtk_rng_cleanup;
-#endif
-	priv->rng.read = mtk_rng_read;
 	priv->rng.quality = 900;
-
-	priv->clk = devm_clk_get(&pdev->dev, "rng");
-	if (IS_ERR(priv->clk)) {
-		ret = PTR_ERR(priv->clk);
-		dev_err(&pdev->dev, "no clock for device: %d\n", ret);
-		return ret;
+	priv->flags = (unsigned long)device_get_match_data(&pdev->dev);
+
+	if (!(priv->flags & MTK_RNG_SMC)) {
+		priv->clk = devm_clk_get(&pdev->dev, "rng");
+		if (IS_ERR(priv->clk)) {
+			ret = PTR_ERR(priv->clk);
+			dev_err(&pdev->dev, "no clock for device: %d\n", ret);
+			return ret;
+		}
+
+		priv->base = devm_platform_ioremap_resource(pdev, 0);
+		if (IS_ERR(priv->base))
+			return PTR_ERR(priv->base);
+
+		if (IS_ENABLED(CONFIG_HAVE_ARM_SMCCC) &&
+		    of_device_is_compatible(pdev->dev.of_node,
+					    "mediatek,mt7986-rng") &&
+		    !mtk_rng_hw_accessible(priv)) {
+			priv->flags |= MTK_RNG_SMC;
+			dev_info(&pdev->dev,
+				 "HW RNG not MMIO accessible, using SMC\n");
+		}
 	}
 
-	priv->base = devm_platform_ioremap_resource(pdev, 0);
-	if (IS_ERR(priv->base))
-		return PTR_ERR(priv->base);
+	if (priv->flags & MTK_RNG_SMC) {
+		if (!IS_ENABLED(CONFIG_HAVE_ARM_SMCCC))
+			return -ENODEV;
+		priv->rng.read = mtk_rng_read_smc;
+	} else {
+#ifndef CONFIG_PM
+		priv->rng.init = mtk_rng_init;
+		priv->rng.cleanup = mtk_rng_cleanup;
+#endif
+		priv->rng.read = mtk_rng_read;
+	}
 
 	ret = devm_hwrng_register(&pdev->dev, &priv->rng);
 	if (ret) {
@@ -139,12 +217,15 @@ static int mtk_rng_probe(struct platform_device *pdev)
 		return ret;
 	}
 
-	dev_set_drvdata(&pdev->dev, priv);
-	pm_runtime_set_autosuspend_delay(&pdev->dev, RNG_AUTOSUSPEND_TIMEOUT);
-	pm_runtime_use_autosuspend(&pdev->dev);
-	ret = devm_pm_runtime_enable(&pdev->dev);
-	if (ret)
-		return ret;
+	if (!(priv->flags & MTK_RNG_SMC)) {
+		dev_set_drvdata(&pdev->dev, priv);
+		pm_runtime_set_autosuspend_delay(&pdev->dev,
+						 RNG_AUTOSUSPEND_TIMEOUT);
+		pm_runtime_use_autosuspend(&pdev->dev);
+		ret = devm_pm_runtime_enable(&pdev->dev);
+		if (ret)
+			return ret;
+	}
 
 	dev_info(&pdev->dev, "registered RNG driver\n");
 
@@ -181,8 +262,11 @@ static const struct dev_pm_ops mtk_rng_pm_ops = {
 #endif	/* CONFIG_PM */
 
 static const struct of_device_id mtk_rng_match[] = {
-	{ .compatible = "mediatek,mt7986-rng" },
 	{ .compatible = "mediatek,mt7623-rng" },
+	{ .compatible = "mediatek,mt7981-rng", .data = (void *)MTK_RNG_SMC },
+	{ .compatible = "mediatek,mt7986-rng" },
+	{ .compatible = "mediatek,mt7987-rng", .data = (void *)MTK_RNG_SMC },
+	{ .compatible = "mediatek,mt7988-rng", .data = (void *)MTK_RNG_SMC },
 	{},
 };
 MODULE_DEVICE_TABLE(of, mtk_rng_match);
@@ -200,4 +284,5 @@ module_platform_driver(mtk_rng_driver);
 
 MODULE_DESCRIPTION("Mediatek Random Number Generator Driver");
 MODULE_AUTHOR("Sean Wang <sean.wang@mediatek.com>");
+MODULE_AUTHOR("Daniel Golle <daniel@makrotopia.org>");
 MODULE_LICENSE("GPL");
-- 
2.53.0

Re: [PATCH 1/2] dt-bindings: rng: mtk-rng: add SMC-based TRNG variants

[Krzysztof Kozlowski]

On Wed, Mar 04, 2026 at 12:55:27AM +0000, Daniel Golle wrote:
> diff --git a/Documentation/devicetree/bindings/rng/mtk-rng.yaml b/Documentation/devicetree/bindings/rng/mtk-rng.yaml
> index 7e8dc62e5d3a6..6074758552ac3 100644
> --- a/Documentation/devicetree/bindings/rng/mtk-rng.yaml
> +++ b/Documentation/devicetree/bindings/rng/mtk-rng.yaml
> @@ -11,12 +11,15 @@ maintainers:
>  
>  properties:
>    $nodename:
> -    pattern: "^rng@[0-9a-f]+$"
> +    pattern: "^rng(@[0-9a-f]+)?$"
>  
>    compatible:
>      oneOf:
>        - enum:
>            - mediatek,mt7623-rng
> +          - mediatek,mt7981-rng
> +          - mediatek,mt7987-rng
> +          - mediatek,mt7988-rng

Not compatible with each other?

>        - items:
>            - enum:
>                - mediatek,mt7622-rng
> @@ -38,9 +41,22 @@ properties:
>  
>  required:
>    - compatible
> -  - reg
> -  - clocks
> -  - clock-names
> +
> +allOf:
> +  - if:
> +      properties:
> +        compatible:
> +          not:

Use rather positive list, so drop "not:" and use cntains for only one
compatible - mediatek,mt7623-rng.

> +            contains:
> +              enum:
> +                - mediatek,mt7981-rng
> +                - mediatek,mt7987-rng
> +                - mediatek,mt7988-rng
> +    then:
> +      required:
> +        - reg
> +        - clocks
> +        - clock-names
>  
>  additionalProperties: false
>  
> @@ -53,3 +69,7 @@ examples:
>              clocks = <&infracfg CLK_INFRA_TRNG>;
>              clock-names = "rng";
>      };
> +  - |
> +    rng {
> +            compatible = "mediatek,mt7981-rng";

Use four spaces for indentation.

> +    };
> -- 
> 2.53.0

Re: [PATCH 1/2] dt-bindings: rng: mtk-rng: add SMC-based TRNG variants

[Daniel Golle]

On Wed, Mar 04, 2026 at 12:34:45PM +0100, Krzysztof Kozlowski wrote:
> On Wed, Mar 04, 2026 at 12:55:27AM +0000, Daniel Golle wrote:
> > diff --git a/Documentation/devicetree/bindings/rng/mtk-rng.yaml b/Documentation/devicetree/bindings/rng/mtk-rng.yaml
> > index 7e8dc62e5d3a6..6074758552ac3 100644
> > --- a/Documentation/devicetree/bindings/rng/mtk-rng.yaml
> > +++ b/Documentation/devicetree/bindings/rng/mtk-rng.yaml
> > @@ -11,12 +11,15 @@ maintainers:
> >  
> >  properties:
> >    $nodename:
> > -    pattern: "^rng@[0-9a-f]+$"
> > +    pattern: "^rng(@[0-9a-f]+)?$"
> >  
> >    compatible:
> >      oneOf:
> >        - enum:
> >            - mediatek,mt7623-rng
> > +          - mediatek,mt7981-rng
> > +          - mediatek,mt7987-rng
> > +          - mediatek,mt7988-rng
> 
> Not compatible with each other?

MT7623 is the original hardware first supported in Linux. It can be
accessed via MMIO and requires the clock to be enabled by Linux.

Starting with MT7981 and followed by MT7988 and MT7987 it is
technically the same hardware, but on those ARMv8 SoCs TF-A assigns
the MMIO range of the TRNG to only be accessible from within the
secure/trusted land, and TF-A provides a (vendor-specific) API
allowing non-trusted land (ie. Linux) to acquire random bytes.

With MT7986 they made the unlucky choice to initially allow direct
access to the MMIO range, but later updates to TF-A then also locked
it to secure/trusted land, offering the same API as on the newer SoCs.
So for MT7986 the driver has to try and figure out which convention to
use.


> 
> >        - items:
> >            - enum:
> >                - mediatek,mt7622-rng
> > @@ -38,9 +41,22 @@ properties:
> >  
> >  required:
> >    - compatible
> > -  - reg
> > -  - clocks
> > -  - clock-names
> > +
> > +allOf:
> > +  - if:
> > +      properties:
> > +        compatible:
> > +          not:
> 
> Use rather positive list, so drop "not:" and use cntains for only one
> compatible - mediatek,mt7623-rng.

Ack.

> 
> > +            contains:
> > +              enum:
> > +                - mediatek,mt7981-rng
> > +                - mediatek,mt7987-rng
> > +                - mediatek,mt7988-rng
> > +    then:
> > +      required:
> > +        - reg
> > +        - clocks
> > +        - clock-names
> >  
> >  additionalProperties: false
> >  
> > @@ -53,3 +69,7 @@ examples:
> >              clocks = <&infracfg CLK_INFRA_TRNG>;
> >              clock-names = "rng";
> >      };
> > +  - |
> > +    rng {
> > +            compatible = "mediatek,mt7981-rng";
> 
> Use four spaces for indentation.

Oh sorry, I knew that actually but forgot...

Re: [PATCH 1/2] dt-bindings: rng: mtk-rng: add SMC-based TRNG variants

[Krzysztof Kozlowski]

On 04/03/2026 13:14, Daniel Golle wrote:
> 
> Starting with MT7981 and followed by MT7988 and MT7987 it is
> technically the same hardware, but on those ARMv8 SoCs TF-A assigns

So they are compatible, I presume?

> the MMIO range of the TRNG to only be accessible from within the
> secure/trusted land, and TF-A provides a (vendor-specific) API
> allowing non-trusted land (ie. Linux) to acquire random bytes.
> 
> With MT7986 they made the unlucky choice to initially allow direct
> access to the MMIO range, but later updates to TF-A then also locked
> it to secure/trusted land, offering the same API as on the newer SoCs.
> So for MT7986 the driver has to try and figure out which convention to
> use.
> 



Best regards,
Krzysztof

Re: [PATCH 1/2] dt-bindings: rng: mtk-rng: add SMC-based TRNG variants

[Daniel Golle]

On Wed, Mar 04, 2026 at 01:18:20PM +0100, Krzysztof Kozlowski wrote:
> On 04/03/2026 13:14, Daniel Golle wrote:
> > 
> > Starting with MT7981 and followed by MT7988 and MT7987 it is
> > technically the same hardware, but on those ARMv8 SoCs TF-A assigns
> 
> So they are compatible, I presume?

Yes. MT7988 and MT7987 are just like MT7981 in that regard.

> 
> > the MMIO range of the TRNG to only be accessible from within the
> > secure/trusted land, and TF-A provides a (vendor-specific) API
> > allowing non-trusted land (ie. Linux) to acquire random bytes.
> > 
> > With MT7986 they made the unlucky choice to initially allow direct
> > access to the MMIO range, but later updates to TF-A then also locked
> > it to secure/trusted land, offering the same API as on the newer SoCs.
> > So for MT7986 the driver has to try and figure out which convention to
> > use.
> > 
> 
> 
> 
> Best regards,
> Krzysztof

Re: [PATCH 1/2] dt-bindings: rng: mtk-rng: add SMC-based TRNG variants

[Krzysztof Kozlowski]

On 04/03/2026 13:21, Daniel Golle wrote:
> On Wed, Mar 04, 2026 at 01:18:20PM +0100, Krzysztof Kozlowski wrote:
>> On 04/03/2026 13:14, Daniel Golle wrote:
>>>
>>> Starting with MT7981 and followed by MT7988 and MT7987 it is
>>> technically the same hardware, but on those ARMv8 SoCs TF-A assigns
>>
>> So they are compatible, I presume?
> 
> Yes. MT7988 and MT7987 are just like MT7981 in that regard.

Then please express it with fallback.

Best regards,
Krzysztof