1 files changed, 239 insertions, 0 deletions
diff --git a/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c b/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
new file mode 100644
index 000000000000..4d9eb0137f8c
--- /dev/null
+++ b/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c
@@ -0,0 +1,239 @@
+/*
+ * Copyright 2021 Advanced Micro Devices, Inc.
+ *
+ * Permission is hereby granted, free of charge, to any person obtaining a
+ * copy of this software and associated documentation files (the "Software"),
+ * to deal in the Software without restriction, including without limitation
+ * the rights to use, copy, modify, merge, publish, distribute, sublicense,
+ * and/or sell copies of the Software, and to permit persons to whom the
+ * Software is furnished to do so, subject to the following conditions:
+ *
+ * The above copyright notice and this permission notice shall be included in
+ * all copies or substantial portions of the Software.
+ *
+ * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+ * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+ * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
+ * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
+ * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
+ * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
+ * OTHER DEALINGS IN THE SOFTWARE.
+ *
+ */
+
+#include "amdgpu_eeprom.h"
+#include "amdgpu.h"
+
+/* AT24CM02 and M24M02-R have a 256-byte write page size.
+ */
+#define EEPROM_PAGE_BITS   8
+#define EEPROM_PAGE_SIZE   (1U << EEPROM_PAGE_BITS)
+#define EEPROM_PAGE_MASK   (EEPROM_PAGE_SIZE - 1)
+
+#define EEPROM_OFFSET_SIZE 2
+
+/* EEPROM memory addresses are 19-bits long, which can
+ * be partitioned into 3, 8, 8 bits, for a total of 19.
+ * The upper 3 bits are sent as part of the 7-bit
+ * "Device Type Identifier"--an I2C concept, which for EEPROM devices
+ * is hard-coded as 1010b, indicating that it is an EEPROM
+ * device--this is the wire format, followed by the upper
+ * 3 bits of the 19-bit address, followed by the direction,
+ * followed by two bytes holding the rest of the 16-bits of
+ * the EEPROM memory address. The format on the wire for EEPROM
+ * devices is: 1010XYZD, A15:A8, A7:A0,
+ * Where D is the direction and sequenced out by the hardware.
+ * Bits XYZ are memory address bits 18, 17 and 16.
+ * These bits are compared to how pins 1-3 of the part are connected,
+ * depending on the size of the part, more on that later.
+ *
+ * Note that of this wire format, a client is in control
+ * of, and needs to specify only XYZ, A15:A8, A7:0, bits,
+ * which is exactly the EEPROM memory address, or offset,
+ * in order to address up to 8 EEPROM devices on the I2C bus.
+ *
+ * For instance, a 2-Mbit I2C EEPROM part, addresses all its bytes,
+ * using an 18-bit address, bit 17 to 0 and thus would use all but one bit of
+ * the 19 bits previously mentioned. The designer would then not connect
+ * pins 1 and 2, and pin 3 usually named "A_2" or "E2", would be connected to
+ * either Vcc or GND. This would allow for up to two 2-Mbit parts on
+ * the same bus, where one would be addressable with bit 18 as 1, and
+ * the other with bit 18 of the address as 0.
+ *
+ * For a 2-Mbit part, bit 18 is usually known as the "Chip Enable" or
+ * "Hardware Address Bit". This bit is compared to the load on pin 3
+ * of the device, described above, and if there is a match, then this
+ * device responds to the command. This way, you can connect two
+ * 2-Mbit EEPROM devices on the same bus, but see one contiguous
+ * memory from 0 to 7FFFFh, where address 0 to 3FFFF is in the device
+ * whose pin 3 is connected to GND, and address 40000 to 7FFFFh is in
+ * the 2nd device, whose pin 3 is connected to Vcc.
+ *
+ * This addressing you encode in the 32-bit "eeprom_addr" below,
+ * namely the 19-bits "XYZ,A15:A0", as a single 19-bit address. For
+ * instance, eeprom_addr = 0x6DA01, is 110_1101_1010_0000_0001, where
+ * XYZ=110b, and A15:A0=DA01h. The XYZ bits become part of the device
+ * address, and the rest of the address bits are sent as the memory
+ * address bytes.
+ *
+ * That is, for an I2C EEPROM driver everything is controlled by
+ * the "eeprom_addr".
+ *
+ * P.S. If you need to write, lock and read the Identification Page,
+ * (M24M02-DR device only, which we do not use), change the "7" to
+ * "0xF" in the macro below, and let the client set bit 20 to 1 in
+ * "eeprom_addr", and set A10 to 0 to write into it, and A10 and A1 to
+ * 1 to lock it permanently.
+ */
+#define MAKE_I2C_ADDR(_aa) ((0xA << 3) | (((_aa) >> 16) & 7))
+
+static int __amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap, u32 eeprom_addr,
+				u8 *eeprom_buf, u16 buf_size, bool read)
+{
+	u8 eeprom_offset_buf[EEPROM_OFFSET_SIZE];
+	struct i2c_msg msgs[] = {
+		{
+			.flags = 0,
+			.len = EEPROM_OFFSET_SIZE,
+			.buf = eeprom_offset_buf,
+		},
+		{
+			.flags = read ? I2C_M_RD : 0,
+		},
+	};
+	const u8 *p = eeprom_buf;
+	int r;
+	u16 len;
+
+	for (r = 0; buf_size > 0;
+	      buf_size -= len, eeprom_addr += len, eeprom_buf += len) {
+		/* Set the EEPROM address we want to write to/read from.
+		 */
+		msgs[0].addr = MAKE_I2C_ADDR(eeprom_addr);
+		msgs[1].addr = msgs[0].addr;
+		msgs[0].buf[0] = (eeprom_addr >> 8) & 0xff;
+		msgs[0].buf[1] = eeprom_addr & 0xff;
+
+		if (!read) {
+			/* Write the maximum amount of data, without
+			 * crossing the device's page boundary, as per
+			 * its spec. Partial page writes are allowed,
+			 * starting at any location within the page,
+			 * so long as the page boundary isn't crossed
+			 * over (actually the page pointer rolls
+			 * over).
+			 *
+			 * As per the AT24CM02 EEPROM spec, after
+			 * writing into a page, the I2C driver should
+			 * terminate the transfer, i.e. in
+			 * "i2c_transfer()" below, with a STOP
+			 * condition, so that the self-timed write
+			 * cycle begins. This is implied for the
+			 * "i2c_transfer()" abstraction.
+			 */
+			len = min(EEPROM_PAGE_SIZE - (eeprom_addr &
+						      EEPROM_PAGE_MASK),
+				  (u32)buf_size);
+		} else {
+			/* Reading from the EEPROM has no limitation
+			 * on the number of bytes read from the EEPROM
+			 * device--they are simply sequenced out.
+			 */
+			len = buf_size;
+		}
+		msgs[1].len = len;
+		msgs[1].buf = eeprom_buf;
+
+		/* This constitutes a START-STOP transaction.
+		 */
+		r = i2c_transfer(i2c_adap, msgs, ARRAY_SIZE(msgs));
+		if (r != ARRAY_SIZE(msgs))
+			break;
+
+		if (!read) {
+			/* According to EEPROM specs the length of the
+			 * self-writing cycle, tWR (tW), is 10 ms.
+			 *
+			 * TODO: Use polling on ACK, aka Acknowledge
+			 * Polling, to minimize waiting for the
+			 * internal write cycle to complete, as it is
+			 * usually smaller than tWR (tW).
+			 */
+			msleep(10);
+		}
+	}
+
+	return r < 0 ? r : eeprom_buf - p;
+}
+
+/**
+ * amdgpu_eeprom_xfer -- Read/write from/to an I2C EEPROM device
+ * @i2c_adap: pointer to the I2C adapter to use
+ * @eeprom_addr: EEPROM address from which to read/write
+ * @eeprom_buf: pointer to data buffer to read into/write from
+ * @buf_size: the size of @eeprom_buf
+ * @read: True if reading from the EEPROM, false if writing
+ *
+ * Returns the number of bytes read/written; -errno on error.
+ */
+static int amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap, u32 eeprom_addr,
+			      u8 *eeprom_buf, u16 buf_size, bool read)
+{
+	const struct i2c_adapter_quirks *quirks = i2c_adap->quirks;
+	u16 limit;
+
+	if (!quirks)
+		limit = 0;
+	else if (read)
+		limit = quirks->max_read_len;
+	else
+		limit = quirks->max_write_len;
+
+	if (limit == 0) {
+		return __amdgpu_eeprom_xfer(i2c_adap, eeprom_addr,
+					    eeprom_buf, buf_size, read);
+	} else if (limit <= EEPROM_OFFSET_SIZE) {
+		dev_err_ratelimited(&i2c_adap->dev,
+				    "maddr:0x%04X size:0x%02X:quirk max_%s_len must be > %d",
+				    eeprom_addr, buf_size,
+				    read ? "read" : "write", EEPROM_OFFSET_SIZE);
+		return -EINVAL;
+	} else {
+		u16 ps; /* Partial size */
+		int res = 0, r;
+
+		/* The "limit" includes all data bytes sent/received,
+		 * which would include the EEPROM_OFFSET_SIZE bytes.
+		 * Account for them here.
+		 */
+		limit -= EEPROM_OFFSET_SIZE;
+		for ( ; buf_size > 0;
+		      buf_size -= ps, eeprom_addr += ps, eeprom_buf += ps) {
+			ps = min(limit, buf_size);
+
+			r = __amdgpu_eeprom_xfer(i2c_adap, eeprom_addr,
+						 eeprom_buf, ps, read);
+			if (r < 0)
+				return r;
+			res += r;
+		}
+
+		return res;
+	}
+}
+
+int amdgpu_eeprom_read(struct i2c_adapter *i2c_adap,
+		       u32 eeprom_addr, u8 *eeprom_buf,
+		       u16 bytes)
+{
+	return amdgpu_eeprom_xfer(i2c_adap, eeprom_addr, eeprom_buf, bytes,
+				  true);
+}
+
+int amdgpu_eeprom_write(struct i2c_adapter *i2c_adap,
+			u32 eeprom_addr, u8 *eeprom_buf,
+			u16 bytes)
+{
+	return amdgpu_eeprom_xfer(i2c_adap, eeprom_addr, eeprom_buf, bytes,
+				  false);
+}