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 * See also top of amdgpu_ras_eeprom.c.
83 *
84 * P.S. If you need to write, lock and read the Identification Page,
85 * (M24M02-DR device only, which we do not use), change the "7" to
86 * "0xF" in the macro below, and let the client set bit 20 to 1 in
87 * "eeprom_addr", and set A10 to 0 to write into it, and A10 and A1 to
88 * 1 to lock it permanently.
89 */
90#define MAKE_I2C_ADDR(_aa) ((0xA << 3) | (((_aa) >> 16) & 0xF))
91
92static int __amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap, u32 eeprom_addr,
93 u8 *eeprom_buf, u32 buf_size, bool read)
94{
95 u8 eeprom_offset_buf[EEPROM_OFFSET_SIZE];
96 struct i2c_msg msgs[] = {
97 {
98 .flags = 0,
99 .len = EEPROM_OFFSET_SIZE,
100 .buf = eeprom_offset_buf,
101 },
102 {
103 .flags = read ? I2C_M_RD : 0,
104 },
105 };
106 const u8 *p = eeprom_buf;
107 int r;
108 u16 len;
109
110 for (r = 0; buf_size > 0;
111 buf_size -= len, eeprom_addr += len, eeprom_buf += len) {
112 /* Set the EEPROM address we want to write to/read from.
113 */
114 msgs[0].addr = MAKE_I2C_ADDR(eeprom_addr);
115 msgs[1].addr = msgs[0].addr;
116 msgs[0].buf[0] = (eeprom_addr >> 8) & 0xff;
117 msgs[0].buf[1] = eeprom_addr & 0xff;
118
119 if (!read) {
120 /* Write the maximum amount of data, without
121 * crossing the device's page boundary, as per
122 * its spec. Partial page writes are allowed,
123 * starting at any location within the page,
124 * so long as the page boundary isn't crossed
125 * over (actually the page pointer rolls
126 * over).
127 *
128 * As per the AT24CM02 EEPROM spec, after
129 * writing into a page, the I2C driver should
130 * terminate the transfer, i.e. in
131 * "i2c_transfer()" below, with a STOP
132 * condition, so that the self-timed write
133 * cycle begins. This is implied for the
134 * "i2c_transfer()" abstraction.
135 */
136 len = min(EEPROM_PAGE_SIZE - (eeprom_addr & EEPROM_PAGE_MASK),
137 buf_size);
138 } else {
139 /* Reading from the EEPROM has no limitation
140 * on the number of bytes read from the EEPROM
141 * device--they are simply sequenced out.
142 * Keep in mind that i2c_msg.len is u16 type.
143 */
144 len = min(U16_MAX, buf_size);
145 }
146 msgs[1].len = len;
147 msgs[1].buf = eeprom_buf;
148
149 /* This constitutes a START-STOP transaction.
150 */
151 r = i2c_transfer(adap: i2c_adap, msgs, ARRAY_SIZE(msgs));
152 if (r != ARRAY_SIZE(msgs))
153 break;
154
155 if (!read) {
156 /* According to EEPROM specs the length of the
157 * self-writing cycle, tWR (tW), is 10 ms.
158 *
159 * TODO: Use polling on ACK, aka Acknowledge
160 * Polling, to minimize waiting for the
161 * internal write cycle to complete, as it is
162 * usually smaller than tWR (tW).
163 */
164 msleep(msecs: 10);
165 }
166 }
167
168 return r < 0 ? r : eeprom_buf - p;
169}
170
171/**
172 * amdgpu_eeprom_xfer -- Read/write from/to an I2C EEPROM device
173 * @i2c_adap: pointer to the I2C adapter to use
174 * @eeprom_addr: EEPROM address from which to read/write
175 * @eeprom_buf: pointer to data buffer to read into/write from
176 * @buf_size: the size of @eeprom_buf
177 * @read: True if reading from the EEPROM, false if writing
178 *
179 * Returns the number of bytes read/written; -errno on error.
180 */
181static int amdgpu_eeprom_xfer(struct i2c_adapter *i2c_adap, u32 eeprom_addr,
182 u8 *eeprom_buf, u32 buf_size, bool read)
183{
184 const struct i2c_adapter_quirks *quirks = i2c_adap->quirks;
185 u16 limit;
186 u16 ps; /* Partial size */
187 int res = 0, r;
188
189 if (!quirks)
190 limit = 0;
191 else if (read)
192 limit = quirks->max_read_len;
193 else
194 limit = quirks->max_write_len;
195
196 if (limit == 0) {
197 return __amdgpu_eeprom_xfer(i2c_adap, eeprom_addr,
198 eeprom_buf, buf_size, read);
199 } else if (limit <= EEPROM_OFFSET_SIZE) {
200 dev_err_ratelimited(&i2c_adap->dev,
201 "maddr:0x%04X size:0x%02X:quirk max_%s_len must be > %d",
202 eeprom_addr, buf_size,
203 str_read_write(read), EEPROM_OFFSET_SIZE);
204 return -EINVAL;
205 }
206
207 /* The "limit" includes all data bytes sent/received,
208 * which would include the EEPROM_OFFSET_SIZE bytes.
209 * Account for them here.
210 */
211 limit -= EEPROM_OFFSET_SIZE;
212 for ( ; buf_size > 0;
213 buf_size -= ps, eeprom_addr += ps, eeprom_buf += ps) {
214 ps = min(limit, buf_size);
215
216 r = __amdgpu_eeprom_xfer(i2c_adap, eeprom_addr,
217 eeprom_buf, buf_size: ps, read);
218 if (r < 0)
219 return r;
220 res += r;
221 }
222
223 return res;
224}
225
226int amdgpu_eeprom_read(struct i2c_adapter *i2c_adap,
227 u32 eeprom_addr, u8 *eeprom_buf,
228 u32 bytes)
229{
230 return amdgpu_eeprom_xfer(i2c_adap, eeprom_addr, eeprom_buf, buf_size: bytes,
231 read: true);
232}
233
234int amdgpu_eeprom_write(struct i2c_adapter *i2c_adap,
235 u32 eeprom_addr, u8 *eeprom_buf,
236 u32 bytes)
237{
238 return amdgpu_eeprom_xfer(i2c_adap, eeprom_addr, eeprom_buf, buf_size: bytes,
239 read: false);
240}
241

source code of linux/drivers/gpu/drm/amd/amdgpu/amdgpu_eeprom.c