linux-kernel - [PATCH v2 2/2] platform/chrome: cros_ec_lpcs: reserve the MEC LPC I/O ports first

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Date:   Wed, 26 Jan 2022 12:00:20 -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>,
        Tzung-Bi Shih <tzungbi@...gle.com>,
        Michael Niksa <michael.niksa@...e.com>,
        "Dustin L. Howett" <dustin@...ett.net>
Subject: [PATCH v2 2/2] platform/chrome: cros_ec_lpcs: reserve the MEC LPC I/O ports first

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.

This patch also fixes an issue where we would interact with I/O ports
0x800-0x807 without first making a reservation.

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