linux-kernel - [PATCH 2/2] platform/chrome: reserve only the I/O ports required for the MEC EC

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Message-Id: <20220105031242.287751-3-dustin@howett.net>
Date:   Tue,  4 Jan 2022 21:12:42 -0600
From:   "Dustin L. Howett" <dustin@...ett.net>
To:     linux-kernel@...r.kernel.org
Cc:     Benson Leung <bleung@...omium.org>,
        Guenter Roeck <groeck@...omium.org>,
        "Dustin L. Howett" <dustin@...ett.net>
Subject: [PATCH 2/2] platform/chrome: reserve only the I/O ports required for the MEC EC

Some ChromeOS EC devices (such as the Framework Laptop) only map I/O
ports 0x800-0x807. Making the larger reservation required by the non-MEC
LPC (the 0xFF ports for the memory map, and the 0xFF ports for the
parameter region) is non-viable on these devices.

Since we probe the MEC EC first, we can get away with a smaller
reservation that covers the MEC EC ports. If we fall back to classic
LPC, we can grow the reservation to cover the memory map and the
parameter region.

Signed-off-by: Dustin L. Howett <dustin@...ett.net>
---
 drivers/platform/chrome/cros_ec_lpc.c         | 39 ++++++++++++-------
 .../linux/platform_data/cros_ec_commands.h    |  4 ++
 2 files changed, 30 insertions(+), 13 deletions(-)

diff --git a/drivers/platform/chrome/cros_ec_lpc.c b/drivers/platform/chrome/cros_ec_lpc.c
index 458eb59db2ff..06fdfe365710 100644
--- a/drivers/platform/chrome/cros_ec_lpc.c
+++ b/drivers/platform/chrome/cros_ec_lpc.c
@@ -341,9 +341,14 @@ static int cros_ec_lpc_probe(struct platform_device *pdev)
 	u8 buf[2];
 	int irq, ret;
 
-	if (!devm_request_region(dev, EC_LPC_ADDR_MEMMAP, EC_MEMMAP_SIZE,
-				 dev_name(dev))) {
-		dev_err(dev, "couldn't reserve memmap region\n");
+	/*
+	 * The Framework Laptop (and possibly other non-ChromeOS devices)
+	 * only exposes the eight I/O ports that are required for the Microchip EC.
+	 * Requesting a larger reservation will fail.
+	 */
+	if (!devm_request_region(dev, EC_HOST_CMD_REGION0,
+				 EC_HOST_CMD_MEC_REGION_SIZE, dev_name(dev))) {
+		dev_err(dev, "couldn't reserve MEC region\n");
 		return -EBUSY;
 	}
 
@@ -357,6 +362,12 @@ static int cros_ec_lpc_probe(struct platform_device *pdev)
 	cros_ec_lpc_ops.write = cros_ec_lpc_mec_write_bytes;
 	cros_ec_lpc_ops.read(EC_LPC_ADDR_MEMMAP + EC_MEMMAP_ID, 2, buf);
 	if (buf[0] != 'E' || buf[1] != 'C') {
+		if (!devm_request_region(dev, EC_LPC_ADDR_MEMMAP, EC_MEMMAP_SIZE,
+					 dev_name(dev))) {
+			dev_err(dev, "couldn't reserve memmap region\n");
+			return -EBUSY;
+		}
+
 		/* Re-assign read/write operations for the non MEC variant */
 		cros_ec_lpc_ops.read = cros_ec_lpc_read_bytes;
 		cros_ec_lpc_ops.write = cros_ec_lpc_write_bytes;
@@ -366,17 +377,19 @@ static int cros_ec_lpc_probe(struct platform_device *pdev)
 			dev_err(dev, "EC ID not detected\n");
 			return -ENODEV;
 		}
-	}
 
-	if (!devm_request_region(dev, EC_HOST_CMD_REGION0,
-				 EC_HOST_CMD_REGION_SIZE, dev_name(dev))) {
-		dev_err(dev, "couldn't reserve region0\n");
-		return -EBUSY;
-	}
-	if (!devm_request_region(dev, EC_HOST_CMD_REGION1,
-				 EC_HOST_CMD_REGION_SIZE, dev_name(dev))) {
-		dev_err(dev, "couldn't reserve region1\n");
-		return -EBUSY;
+		/* Reserve the remaining I/O ports required by the non-MEC protocol. */
+		if (!devm_request_region(dev, EC_HOST_CMD_REGION0 + EC_HOST_CMD_MEC_REGION_SIZE,
+					 EC_HOST_CMD_REGION_SIZE - EC_HOST_CMD_MEC_REGION_SIZE,
+					 dev_name(dev))) {
+			dev_err(dev, "couldn't reserve remainder of region0\n");
+			return -EBUSY;
+		}
+		if (!devm_request_region(dev, EC_HOST_CMD_REGION1,
+					 EC_HOST_CMD_REGION_SIZE, dev_name(dev))) {
+			dev_err(dev, "couldn't reserve region1\n");
+			return -EBUSY;
+		}
 	}
 
 	ec_dev = devm_kzalloc(dev, sizeof(*ec_dev), GFP_KERNEL);
diff --git a/include/linux/platform_data/cros_ec_commands.h b/include/linux/platform_data/cros_ec_commands.h
index 271bd87bff0a..a85b1176e6c0 100644
--- a/include/linux/platform_data/cros_ec_commands.h
+++ b/include/linux/platform_data/cros_ec_commands.h
@@ -55,6 +55,10 @@
 #define EC_HOST_CMD_REGION0    0x800
 #define EC_HOST_CMD_REGION1    0x880
 #define EC_HOST_CMD_REGION_SIZE 0x80
+/*
+ * Other machines report only the region spanned by the Microchip MEC EC.
+ */
+#define EC_HOST_CMD_MEC_REGION_SIZE 0x08
 
 /* EC command register bit functions */
 #define EC_LPC_CMDR_DATA	BIT(0)  /* Data ready for host to read */
-- 
2.34.1