[PATCH 2/2] hwrng: msm: add ACPI support

[Timur Tabi <timur@codeaurora.org>]

Add support for probing on ACPI systems, with ACPI HID QCOM8160.

On ACPI systems, clocks are always enabled, the PRNG should
already be enabled, and the register region is read-only.
The driver only verifies that the hardware is already
enabled never tries to disable or configure it.

Signed-off-by: Timur Tabi <timur@codeaurora.org>
---
 drivers/char/hw_random/msm-rng.c | 40 ++++++++++++++++++++++++++++++++++------
 1 file changed, 34 insertions(+), 6 deletions(-)

diff --git a/drivers/char/hw_random/msm-rng.c b/drivers/char/hw_random/msm-rng.c
index 44580588b938..f34713d23d77 100644
--- a/drivers/char/hw_random/msm-rng.c
+++ b/drivers/char/hw_random/msm-rng.c
@@ -20,6 +20,7 @@
 #include <linux/of.h>
 #include <linux/platform_device.h>
 #include <linux/spinlock.h>
+#include <linux/acpi.h>
 
 /* Device specific register offsets */
 #define PRNG_DATA_OUT		0x0000
@@ -186,16 +187,32 @@ static int msm_rng_probe(struct platform_device *pdev)
 	if (IS_ERR(rng->base))
 		return PTR_ERR(rng->base);
 
-	rng->clk = devm_clk_get(&pdev->dev, "core");
-	if (IS_ERR(rng->clk))
-		return PTR_ERR(rng->clk);
-
 	rng->hwrng.name = KBUILD_MODNAME;
-	rng->hwrng.init = msm_rng_init;
-	rng->hwrng.cleanup = msm_rng_cleanup;
 	rng->hwrng.read = msm_rng_read;
 	spin_lock_init(&rng->lock);
 
+	/*
+	 * ACPI systems have v2 hardware. The clocks are always enabled,
+	 * the PRNG register space is read-only, and the PRNG should
+	 * already be enabled.
+	 */
+	if (has_acpi_companion(&pdev->dev)) {
+		u32 val;
+
+		val = readl(rng->base + PRNG_CONFIG);
+		if (!(val & PRNG_CONFIG_HW_ENABLE)) {
+			dev_err(&pdev->dev, "device is not enabled\n");
+			return -ENODEV;
+		}
+	} else {
+		rng->clk = devm_clk_get(&pdev->dev, "core");
+		if (IS_ERR(rng->clk))
+			return PTR_ERR(rng->clk);
+
+		rng->hwrng.init = msm_rng_init;
+		rng->hwrng.cleanup = msm_rng_cleanup;
+	}
+
 	ret = devm_hwrng_register(&pdev->dev, &rng->hwrng);
 	if (ret) {
 		dev_err(&pdev->dev, "failed to register hwrng\n");
@@ -211,11 +228,22 @@ static int msm_rng_probe(struct platform_device *pdev)
 };
 MODULE_DEVICE_TABLE(of, msm_rng_of_match);
 
+#if IS_ENABLED(CONFIG_ACPI)
+static const struct acpi_device_id msm_rng_acpi_match[] = {
+	{
+		.id = "QCOM8160",	/* v2 PRNG */
+	},
+	{}
+};
+MODULE_DEVICE_TABLE(acpi, msm_rng_acpi_match);
+#endif
+
 static struct platform_driver msm_rng_driver = {
 	.probe = msm_rng_probe,
 	.driver = {
 		.name = KBUILD_MODNAME,
 		.of_match_table = of_match_ptr(msm_rng_of_match),
+		.acpi_match_table = ACPI_PTR(msm_rng_acpi_match),
 	}
 };
 module_platform_driver(msm_rng_driver);
-- 
Qualcomm Datacenter Technologies, Inc. as an affiliate of Qualcomm
Technologies, Inc.  Qualcomm Technologies, Inc. is a member of the
Code Aurora Forum, a Linux Foundation Collaborative Project.