soc: apple: Add RTKit helper driver

This driver can be used for coprocessors that do some background task or
communicate out-of-band, and do not do any mailbox I/O beyond the
standard RTKit initialization.

Signed-off-by: Hector Martin <marcan@marcan.st>

Author: marcan

drivers/soc/apple/Kconfig

@@ -37,6 +37,19 @@ config APPLE_RTKIT
 
 	  Say 'y' here if you have an Apple SoC.
 
+config APPLE_RTKIT_HELPER
+	tristate "Apple Generic RTKit helper co-processor"
+	depends on APPLE_RTKIT
+	depends on ARCH_APPLE || COMPILE_TEST
+	help
+	  Apple SoCs such as the M1 come with various co-processors running
+	  their proprietary RTKit operating system. This option enables support
+	  for a generic co-processor that does not implement any additional
+	  in-band communications. It can be used for testing purposes, or for
+	  coprocessors such as MTP that communicate over a different interface.
+
+	  Say 'y' here if you have an Apple SoC.
+
 config APPLE_SART
 	tristate "Apple SART DMA address filter"
 	depends on ARCH_APPLE || COMPILE_TEST

drivers/soc/apple/Makefile

@@ -9,5 +9,8 @@ apple-mailbox-y = mailbox.o
 obj-$(CONFIG_APPLE_RTKIT) += apple-rtkit.o
 apple-rtkit-y = rtkit.o rtkit-crashlog.o
 
+obj-$(CONFIG_APPLE_RTKIT_HELPER) += apple-rtkit-helper.o
+apple-rtkit-helper-y = rtkit-helper.o
+
 obj-$(CONFIG_APPLE_SART) += apple-sart.o
 apple-sart-y = sart.o

drivers/soc/apple/rtkit-helper.c

@@ -0,0 +1,151 @@
+// SPDX-License-Identifier: GPL-2.0-only OR MIT
+/*
+ * Apple Generic RTKit helper coprocessor
+ * Copyright The Asahi Linux Contributors
+ */
+
+#include <linux/device.h>
+#include <linux/dma-mapping.h>
+#include <linux/io.h>
+#include <linux/ioport.h>
+#include <linux/of.h>
+#include <linux/of_platform.h>
+#include <linux/platform_device.h>
+#include <linux/soc/apple/rtkit.h>
+
+#define APPLE_ASC_CPU_CONTROL		0x44
+#define APPLE_ASC_CPU_CONTROL_RUN	BIT(4)
+
+struct apple_rtkit_helper {
+	struct device *dev;
+	struct apple_rtkit *rtk;
+
+	void __iomem *asc_base;
+
+	struct resource *sram;
+	void __iomem *sram_base;
+};
+
+static int apple_rtkit_helper_shmem_setup(void *cookie, struct apple_rtkit_shmem *bfr)
+{
+	struct apple_rtkit_helper *helper = cookie;
+	struct resource res = {
+		.start = bfr->iova,
+		.end = bfr->iova + bfr->size - 1,
+		.name = "rtkit_map",
+	};
+
+	if (!bfr->iova) {
+		bfr->buffer = dma_alloc_coherent(helper->dev, bfr->size,
+						    &bfr->iova, GFP_KERNEL);
+		if (!bfr->buffer)
+			return -ENOMEM;
+		return 0;
+	}
+
+	if (!helper->sram) {
+		dev_err(helper->dev,
+			"RTKit buffer request with no SRAM region: %pR", &res);
+		return -EFAULT;
+	}
+
+	res.flags = helper->sram->flags;
+
+	if (res.end < res.start || !resource_contains(helper->sram, &res)) {
+		dev_err(helper->dev,
+			"RTKit buffer request outside SRAM region: %pR", &res);
+		return -EFAULT;
+	}
+
+	bfr->iomem = helper->sram_base + (res.start - helper->sram->start);
+	bfr->is_mapped = true;
+
+	return 0;
+}
+
+static void apple_rtkit_helper_shmem_destroy(void *cookie, struct apple_rtkit_shmem *bfr)
+{
+	// no-op
+}
+
+static const struct apple_rtkit_ops apple_rtkit_helper_ops = {
+	.shmem_setup = apple_rtkit_helper_shmem_setup,
+	.shmem_destroy = apple_rtkit_helper_shmem_destroy,
+};
+
+static int apple_rtkit_helper_probe(struct platform_device *pdev)
+{
+	struct device *dev = &pdev->dev;
+	struct apple_rtkit_helper *helper;
+	int ret;
+
+	/* 44 bits for addresses in standard RTKit requests */
+	ret = dma_set_mask_and_coherent(&pdev->dev, DMA_BIT_MASK(44));
+	if (ret)
+		return ret;
+
+	helper = devm_kzalloc(dev, sizeof(*helper), GFP_KERNEL);
+	if (!helper)
+		return -ENOMEM;
+
+	helper->dev = dev;
+	platform_set_drvdata(pdev, helper);
+
+	helper->asc_base = devm_platform_ioremap_resource_byname(pdev, "asc");
+	if (IS_ERR(helper->asc_base))
+		return PTR_ERR(helper->asc_base);
+
+	helper->sram = platform_get_resource_byname(pdev, IORESOURCE_MEM, "sram");
+	if (helper->sram) {
+		helper->sram_base = devm_ioremap_resource(dev, helper->sram);
+		if (IS_ERR(helper->sram_base))
+			return dev_err_probe(dev, PTR_ERR(helper->sram_base),
+					"Failed to map SRAM region");
+	}
+
+	helper->rtk =
+		devm_apple_rtkit_init(dev, helper, NULL, 0, &apple_rtkit_helper_ops);
+	if (IS_ERR(helper->rtk))
+		return dev_err_probe(dev, PTR_ERR(helper->rtk),
+				     "Failed to intialize RTKit");
+
+	writel_relaxed(APPLE_ASC_CPU_CONTROL_RUN,
+		       helper->asc_base + APPLE_ASC_CPU_CONTROL);
+
+	/* Works for both wake and boot */
+	ret = apple_rtkit_wake(helper->rtk);
+	if (ret != 0)
+		return dev_err_probe(dev, ret, "Failed to wake up coprocessor");
+
+	return 0;
+}
+
+static void apple_rtkit_helper_remove(struct platform_device *pdev)
+{
+	struct apple_rtkit_helper *helper = platform_get_drvdata(pdev);
+
+	if (apple_rtkit_is_running(helper->rtk))
+		apple_rtkit_quiesce(helper->rtk);
+
+	writel_relaxed(0, helper->asc_base + APPLE_ASC_CPU_CONTROL);
+}
+
+static const struct of_device_id apple_rtkit_helper_of_match[] = {
+	{ .compatible = "apple,rtk-helper-asc4" },
+	{},
+};
+MODULE_DEVICE_TABLE(of, apple_rtkit_helper_of_match);
+
+static struct platform_driver apple_rtkit_helper_driver = {
+	.driver = {
+		.name = "rtkit-helper",
+		.of_match_table = apple_rtkit_helper_of_match,
+	},
+	.probe = apple_rtkit_helper_probe,
+	.remove = apple_rtkit_helper_remove,
+};
+module_platform_driver(apple_rtkit_helper_driver);
+
+MODULE_AUTHOR("Hector Martin <marcan@marcan.st>");
+MODULE_LICENSE("Dual MIT/GPL");
+MODULE_DESCRIPTION("Apple RTKit helper driver");