arm: apple: rtkit: Support allocating OSLog out of SRAM in helper

The new OSLog region in MTP (firmware 13.3+) persists on handoff to
Linux. To avoid having to come up with some weird DART handoff or DAPF
tricks, let's just steal some of the coprocessor's dedicated SRAM. This
keeps it happy and Linux doesn't need any special handoff then.

Signed-off-by: Hector Martin <[email protected]>

Author: marcan

arch/arm/mach-apple/rtkit_helper.c

@@ -16,12 +16,60 @@
 #define REG_CPU_CTRL		0x0044
 #define  REG_CPU_CTRL_RUN	BIT(4)
 
+#define APPLE_RTKIT_EP_OSLOG 8
+
 struct rtkit_helper_priv {
 	void *asc;		/* ASC registers */
 	struct mbox_chan chan;
 	struct apple_rtkit *rtk;
+	bool sram_stolen;
 };
 
+static int shmem_setup(void *cookie, struct apple_rtkit_buffer *buf) {
+	struct udevice *dev = cookie;
+	struct rtkit_helper_priv *priv = dev_get_priv(dev);
+
+	if (!buf->is_mapped) {
+		/*
+		 * Special case: The OSLog buffer on MTP persists on Linux handoff.
+		 * Steal some SRAM instead of putting this in DRAM, so we don't
+		 * have to hand off DART/DAPF mappings.
+		 */
+		if (buf->endpoint == APPLE_RTKIT_EP_OSLOG) {
+			if (priv->sram_stolen) {
+				printf("%s: Tried to map more than one OSLog buffer out of SRAM\n",
+				       __func__);
+			} else {
+				fdt_size_t size;
+				fdt_addr_t addr;
+
+				addr = dev_read_addr_size_name(dev, "sram", &size);
+
+				if (addr != FDT_ADDR_T_NONE) {
+					buf->dva = ALIGN_DOWN(addr + size - buf->size, SZ_16K);
+					priv->sram_stolen = true;
+
+					return 0;
+				} else {
+					printf("%s: No SRAM, falling back to DRAM\n", __func__);
+				}
+			}
+		}
+
+		buf->buffer = memalign(SZ_16K, ALIGN(buf->size, SZ_16K));
+		if (!buf->buffer)
+			return -ENOMEM;
+
+		buf->dva = (u64)buf->buffer;
+	}
+	return 0;
+}
+
+static void shmem_destroy(void *cookie, struct apple_rtkit_buffer *buf) {
+	if (buf->buffer)
+		free(buf->buffer);
+}
+
 static int rtkit_helper_probe(struct udevice *dev)
 {
 	struct rtkit_helper_priv *priv = dev_get_priv(dev);
@@ -39,7 +87,7 @@ static int rtkit_helper_probe(struct udevice *dev)
 	ctrl = readl(priv->asc + REG_CPU_CTRL);
 	writel(ctrl | REG_CPU_CTRL_RUN, priv->asc + REG_CPU_CTRL);
 
-	priv->rtk = apple_rtkit_init(&priv->chan, priv, NULL, NULL);
+	priv->rtk = apple_rtkit_init(&priv->chan, dev, shmem_setup, shmem_destroy);
 	if (!priv->rtk)
 		return -ENOMEM;