1 /*
2  * Copyright 2021 Advanced Micro Devices, Inc.
3  *
4  * Permission is hereby granted, free of charge, to any person obtaining a
5  * copy of this software and associated documentation files (the "Software"),
6  * to deal in the Software without restriction, including without limitation
7  * the rights to use, copy, modify, merge, publish, distribute, sublicense,
8  * and/or sell copies of the Software, and to permit persons to whom the
9  * Software is furnished to do so, subject to the following conditions:
10  *
11  * The above copyright notice and this permission notice shall be included in
12  * all copies or substantial portions of the Software.
13  *
14  * THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
15  * IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
16  * FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.  IN NO EVENT SHALL
17  * THE COPYRIGHT HOLDER(S) OR AUTHOR(S) BE LIABLE FOR ANY CLAIM, DAMAGES OR
18  * OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE,
19  * ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR
20  * OTHER DEALINGS IN THE SOFTWARE.
21  *
22  */
23 
24 #include "amdgpu_eeprom.h"
25 #include "amdgpu.h"
26 
27 /* AT24CM02 and M24M02-R have a 256-byte write page size.
28  */
29 #define EEPROM_PAGE_BITS   8
30 #define EEPROM_PAGE_SIZE   (1U << EEPROM_PAGE_BITS)
31 #define EEPROM_PAGE_MASK   (EEPROM_PAGE_SIZE - 1)
32 
33 #define EEPROM_OFFSET_SIZE 2
34 
35 /* EEPROM memory addresses are 19-bits long, which can
36  * be partitioned into 3, 8, 8 bits, for a total of 19.
37  * The upper 3 bits are sent as part of the 7-bit
38  * "Device Type Identifier"--an I2C concept, which for EEPROM devices
39  * is hard-coded as 1010b, indicating that it is an EEPROM
40  * device--this is the wire format, followed by the upper
41  * 3 bits of the 19-bit address, followed by the direction,
42  * followed by two bytes holding the rest of the 16-bits of
43  * the EEPROM memory address. The format on the wire for EEPROM
44  * devices is: 1010XYZD, A15:A8, A7:A0,
45  * Where D is the direction and sequenced out by the hardware.
46  * Bits XYZ are memory address bits 18, 17 and 16.
47  * These bits are compared to how pins 1-3 of the part are connected,
48  * depending on the size of the part, more on that later.
49  *
50  * Note that of this wire format, a client is in control
51  * of, and needs to specify only XYZ, A15:A8, A7:0, bits,
52  * which is exactly the EEPROM memory address, or offset,
53  * in order to address up to 8 EEPROM devices on the I2C bus.
54  *
55  * For instance, a 2-Mbit I2C EEPROM part, addresses all its bytes,
56  * using an 18-bit address, bit 17 to 0 and thus would use all but one bit of
57  * the 19 bits previously mentioned. The designer would then not connect
58  * pins 1 and 2, and pin 3 usually named "A_2" or "E2", would be connected to
59  * either Vcc or GND. This would allow for up to two 2-Mbit parts on
60  * the same bus, where one would be addressable with bit 18 as 1, and
61  * the other with bit 18 of the address as 0.
62  *
63  * For a 2-Mbit part, bit 18 is usually known as the "Chip Enable" or
64  * "Hardware Address Bit". This bit is compared to the load on pin 3
65  * of the device, described above, and if there is a match, then this
66  * device responds to the command. This way, you can connect two
67  * 2-Mbit EEPROM devices on the same bus, but see one contiguous
68  * memory from 0 to 7FFFFh, where address 0 to 3FFFF is in the device
69  * whose pin 3 is connected to GND, and address 40000 to 7FFFFh is in
70  * the 2nd device, whose pin 3 is connected to Vcc.
71  *
72  * This addressing you encode in the 32-bit "eeprom_addr" below,
73  * namely the 19-bits "XYZ,A15:A0", as a single 19-bit address. For
74  * instance, eeprom_addr = 0x6DA01, is 110_1101_1010_0000_0001, where
75  * XYZ=110b, and A15:A0=DA01h. The XYZ bits become part of the device
76  * address, and the rest of the address bits are sent as the memory
77  * address bytes.
78  *
79  * That is, for an I2C EEPROM driver everything is controlled by
80  * the "eeprom_addr".
81  *
82  * P.S. If you need to write, lock and read the Identification Page,
83  * (M24M02-DR device only, which we do not use), change the "7" to
84  * "0xF" in the macro below, and let the client set bit 20 to 1 in
85  * "eeprom_addr", and set A10 to 0 to write into it, and A10 and A1 to
86  * 1 to lock it permanently.
87  */
88 #define MAKE_I2C_ADDR(_aa) ((0xA << 3) | (((_aa) >> 16) & 7))
89 
90 static int __amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap, u32 eeprom_addr,
91 				u8 *eeprom_buf, u16 buf_size, bool read)
92 {
93 	u8 eeprom_offset_buf[EEPROM_OFFSET_SIZE];
94 	struct i2c_msg msgs[] = {
95 		{
96 			.flags = 0,
97 			.len = EEPROM_OFFSET_SIZE,
98 			.buf = eeprom_offset_buf,
99 		},
100 		{
101 			.flags = read ? I2C_M_RD : 0,
102 		},
103 	};
104 	const u8 *p = eeprom_buf;
105 	int r;
106 	u16 len;
107 
108 	for (r = 0; buf_size > 0;
109 	      buf_size -= len, eeprom_addr += len, eeprom_buf += len) {
110 		/* Set the EEPROM address we want to write to/read from.
111 		 */
112 		msgs[0].addr = MAKE_I2C_ADDR(eeprom_addr);
113 		msgs[1].addr = msgs[0].addr;
114 		msgs[0].buf[0] = (eeprom_addr >> 8) & 0xff;
115 		msgs[0].buf[1] = eeprom_addr & 0xff;
116 
117 		if (!read) {
118 			/* Write the maximum amount of data, without
119 			 * crossing the device's page boundary, as per
120 			 * its spec. Partial page writes are allowed,
121 			 * starting at any location within the page,
122 			 * so long as the page boundary isn't crossed
123 			 * over (actually the page pointer rolls
124 			 * over).
125 			 *
126 			 * As per the AT24CM02 EEPROM spec, after
127 			 * writing into a page, the I2C driver should
128 			 * terminate the transfer, i.e. in
129 			 * "i2c_transfer()" below, with a STOP
130 			 * condition, so that the self-timed write
131 			 * cycle begins. This is implied for the
132 			 * "i2c_transfer()" abstraction.
133 			 */
134 			len = min(EEPROM_PAGE_SIZE - (eeprom_addr &
135 						      EEPROM_PAGE_MASK),
136 				  (u32)buf_size);
137 		} else {
138 			/* Reading from the EEPROM has no limitation
139 			 * on the number of bytes read from the EEPROM
140 			 * device--they are simply sequenced out.
141 			 */
142 			len = buf_size;
143 		}
144 		msgs[1].len = len;
145 		msgs[1].buf = eeprom_buf;
146 
147 		/* This constitutes a START-STOP transaction.
148 		 */
149 		r = i2c_transfer(i2c_adap, msgs, ARRAY_SIZE(msgs));
150 		if (r != ARRAY_SIZE(msgs))
151 			break;
152 
153 		if (!read) {
154 			/* According to EEPROM specs the length of the
155 			 * self-writing cycle, tWR (tW), is 10 ms.
156 			 *
157 			 * TODO: Use polling on ACK, aka Acknowledge
158 			 * Polling, to minimize waiting for the
159 			 * internal write cycle to complete, as it is
160 			 * usually smaller than tWR (tW).
161 			 */
162 			msleep(10);
163 		}
164 	}
165 
166 	return r < 0 ? r : eeprom_buf - p;
167 }
168 
169 /**
170  * amdgpu_eeprom_xfer -- Read/write from/to an I2C EEPROM device
171  * @i2c_adap: pointer to the I2C adapter to use
172  * @eeprom_addr: EEPROM address from which to read/write
173  * @eeprom_buf: pointer to data buffer to read into/write from
174  * @buf_size: the size of @eeprom_buf
175  * @read: True if reading from the EEPROM, false if writing
176  *
177  * Returns the number of bytes read/written; -errno on error.
178  */
179 static int amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap, u32 eeprom_addr,
180 			      u8 *eeprom_buf, u16 buf_size, bool read)
181 {
182 	const struct i2c_adapter_quirks *quirks = i2c_adap->quirks;
183 	u16 limit;
184 
185 	if (!quirks)
186 		limit = 0;
187 	else if (read)
188 		limit = quirks->max_read_len;
189 	else
190 		limit = quirks->max_write_len;
191 
192 	if (limit == 0) {
193 		return __amdgpu_eeprom_xfer(i2c_adap, eeprom_addr,
194 					    eeprom_buf, buf_size, read);
195 	} else if (limit <= EEPROM_OFFSET_SIZE) {
196 		dev_err_ratelimited(&i2c_adap->dev,
197 				    "maddr:0x%04X size:0x%02X:quirk max_%s_len must be > %d",
198 				    eeprom_addr, buf_size,
199 				    read ? "read" : "write", EEPROM_OFFSET_SIZE);
200 		return -EINVAL;
201 	} else {
202 		u16 ps; /* Partial size */
203 		int res = 0, r;
204 
205 		/* The "limit" includes all data bytes sent/received,
206 		 * which would include the EEPROM_OFFSET_SIZE bytes.
207 		 * Account for them here.
208 		 */
209 		limit -= EEPROM_OFFSET_SIZE;
210 		for ( ; buf_size > 0;
211 		      buf_size -= ps, eeprom_addr += ps, eeprom_buf += ps) {
212 			ps = min(limit, buf_size);
213 
214 			r = __amdgpu_eeprom_xfer(i2c_adap, eeprom_addr,
215 						 eeprom_buf, ps, read);
216 			if (r < 0)
217 				return r;
218 			res += r;
219 		}
220 
221 		return res;
222 	}
223 }
224 
225 int amdgpu_eeprom_read(struct i2c_adapter *i2c_adap,
226 		       u32 eeprom_addr, u8 *eeprom_buf,
227 		       u16 bytes)
228 {
229 	return amdgpu_eeprom_xfer(i2c_adap, eeprom_addr, eeprom_buf, bytes,
230 				  true);
231 }
232 
233 int amdgpu_eeprom_write(struct i2c_adapter *i2c_adap,
234 			u32 eeprom_addr, u8 *eeprom_buf,
235 			u16 bytes)
236 {
237 	return amdgpu_eeprom_xfer(i2c_adap, eeprom_addr, eeprom_buf, bytes,
238 				  false);
239 }
240