1 /*******************************************************************************
2 
3   Intel(R) Gigabit Ethernet Linux driver
4   Copyright(c) 2007-2012 Intel Corporation.
5 
6   This program is free software; you can redistribute it and/or modify it
7   under the terms and conditions of the GNU General Public License,
8   version 2, as published by the Free Software Foundation.
9 
10   This program is distributed in the hope it will be useful, but WITHOUT
11   ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or
12   FITNESS FOR A PARTICULAR PURPOSE.  See the GNU General Public License for
13   more details.
14 
15   You should have received a copy of the GNU General Public License along with
16   this program; if not, write to the Free Software Foundation, Inc.,
17   51 Franklin St - Fifth Floor, Boston, MA 02110-1301 USA.
18 
19   The full GNU General Public License is included in this distribution in
20   the file called "COPYING".
21 
22   Contact Information:
23   e1000-devel Mailing List <e1000-devel@lists.sourceforge.net>
24   Intel Corporation, 5200 N.E. Elam Young Parkway, Hillsboro, OR 97124-6497
25 
26 *******************************************************************************/
27 
28 #include <linux/if_ether.h>
29 #include <linux/delay.h>
30 
31 #include "e1000_mac.h"
32 #include "e1000_nvm.h"
33 
34 /**
35  *  igb_raise_eec_clk - Raise EEPROM clock
36  *  @hw: pointer to the HW structure
37  *  @eecd: pointer to the EEPROM
38  *
39  *  Enable/Raise the EEPROM clock bit.
40  **/
41 static void igb_raise_eec_clk(struct e1000_hw *hw, u32 *eecd)
42 {
43 	*eecd = *eecd | E1000_EECD_SK;
44 	wr32(E1000_EECD, *eecd);
45 	wrfl();
46 	udelay(hw->nvm.delay_usec);
47 }
48 
49 /**
50  *  igb_lower_eec_clk - Lower EEPROM clock
51  *  @hw: pointer to the HW structure
52  *  @eecd: pointer to the EEPROM
53  *
54  *  Clear/Lower the EEPROM clock bit.
55  **/
56 static void igb_lower_eec_clk(struct e1000_hw *hw, u32 *eecd)
57 {
58 	*eecd = *eecd & ~E1000_EECD_SK;
59 	wr32(E1000_EECD, *eecd);
60 	wrfl();
61 	udelay(hw->nvm.delay_usec);
62 }
63 
64 /**
65  *  igb_shift_out_eec_bits - Shift data bits our to the EEPROM
66  *  @hw: pointer to the HW structure
67  *  @data: data to send to the EEPROM
68  *  @count: number of bits to shift out
69  *
70  *  We need to shift 'count' bits out to the EEPROM.  So, the value in the
71  *  "data" parameter will be shifted out to the EEPROM one bit at a time.
72  *  In order to do this, "data" must be broken down into bits.
73  **/
74 static void igb_shift_out_eec_bits(struct e1000_hw *hw, u16 data, u16 count)
75 {
76 	struct e1000_nvm_info *nvm = &hw->nvm;
77 	u32 eecd = rd32(E1000_EECD);
78 	u32 mask;
79 
80 	mask = 0x01 << (count - 1);
81 	if (nvm->type == e1000_nvm_eeprom_spi)
82 		eecd |= E1000_EECD_DO;
83 
84 	do {
85 		eecd &= ~E1000_EECD_DI;
86 
87 		if (data & mask)
88 			eecd |= E1000_EECD_DI;
89 
90 		wr32(E1000_EECD, eecd);
91 		wrfl();
92 
93 		udelay(nvm->delay_usec);
94 
95 		igb_raise_eec_clk(hw, &eecd);
96 		igb_lower_eec_clk(hw, &eecd);
97 
98 		mask >>= 1;
99 	} while (mask);
100 
101 	eecd &= ~E1000_EECD_DI;
102 	wr32(E1000_EECD, eecd);
103 }
104 
105 /**
106  *  igb_shift_in_eec_bits - Shift data bits in from the EEPROM
107  *  @hw: pointer to the HW structure
108  *  @count: number of bits to shift in
109  *
110  *  In order to read a register from the EEPROM, we need to shift 'count' bits
111  *  in from the EEPROM.  Bits are "shifted in" by raising the clock input to
112  *  the EEPROM (setting the SK bit), and then reading the value of the data out
113  *  "DO" bit.  During this "shifting in" process the data in "DI" bit should
114  *  always be clear.
115  **/
116 static u16 igb_shift_in_eec_bits(struct e1000_hw *hw, u16 count)
117 {
118 	u32 eecd;
119 	u32 i;
120 	u16 data;
121 
122 	eecd = rd32(E1000_EECD);
123 
124 	eecd &= ~(E1000_EECD_DO | E1000_EECD_DI);
125 	data = 0;
126 
127 	for (i = 0; i < count; i++) {
128 		data <<= 1;
129 		igb_raise_eec_clk(hw, &eecd);
130 
131 		eecd = rd32(E1000_EECD);
132 
133 		eecd &= ~E1000_EECD_DI;
134 		if (eecd & E1000_EECD_DO)
135 			data |= 1;
136 
137 		igb_lower_eec_clk(hw, &eecd);
138 	}
139 
140 	return data;
141 }
142 
143 /**
144  *  igb_poll_eerd_eewr_done - Poll for EEPROM read/write completion
145  *  @hw: pointer to the HW structure
146  *  @ee_reg: EEPROM flag for polling
147  *
148  *  Polls the EEPROM status bit for either read or write completion based
149  *  upon the value of 'ee_reg'.
150  **/
151 static s32 igb_poll_eerd_eewr_done(struct e1000_hw *hw, int ee_reg)
152 {
153 	u32 attempts = 100000;
154 	u32 i, reg = 0;
155 	s32 ret_val = -E1000_ERR_NVM;
156 
157 	for (i = 0; i < attempts; i++) {
158 		if (ee_reg == E1000_NVM_POLL_READ)
159 			reg = rd32(E1000_EERD);
160 		else
161 			reg = rd32(E1000_EEWR);
162 
163 		if (reg & E1000_NVM_RW_REG_DONE) {
164 			ret_val = 0;
165 			break;
166 		}
167 
168 		udelay(5);
169 	}
170 
171 	return ret_val;
172 }
173 
174 /**
175  *  igb_acquire_nvm - Generic request for access to EEPROM
176  *  @hw: pointer to the HW structure
177  *
178  *  Set the EEPROM access request bit and wait for EEPROM access grant bit.
179  *  Return successful if access grant bit set, else clear the request for
180  *  EEPROM access and return -E1000_ERR_NVM (-1).
181  **/
182 s32 igb_acquire_nvm(struct e1000_hw *hw)
183 {
184 	u32 eecd = rd32(E1000_EECD);
185 	s32 timeout = E1000_NVM_GRANT_ATTEMPTS;
186 	s32 ret_val = 0;
187 
188 
189 	wr32(E1000_EECD, eecd | E1000_EECD_REQ);
190 	eecd = rd32(E1000_EECD);
191 
192 	while (timeout) {
193 		if (eecd & E1000_EECD_GNT)
194 			break;
195 		udelay(5);
196 		eecd = rd32(E1000_EECD);
197 		timeout--;
198 	}
199 
200 	if (!timeout) {
201 		eecd &= ~E1000_EECD_REQ;
202 		wr32(E1000_EECD, eecd);
203 		hw_dbg("Could not acquire NVM grant\n");
204 		ret_val = -E1000_ERR_NVM;
205 	}
206 
207 	return ret_val;
208 }
209 
210 /**
211  *  igb_standby_nvm - Return EEPROM to standby state
212  *  @hw: pointer to the HW structure
213  *
214  *  Return the EEPROM to a standby state.
215  **/
216 static void igb_standby_nvm(struct e1000_hw *hw)
217 {
218 	struct e1000_nvm_info *nvm = &hw->nvm;
219 	u32 eecd = rd32(E1000_EECD);
220 
221 	if (nvm->type == e1000_nvm_eeprom_spi) {
222 		/* Toggle CS to flush commands */
223 		eecd |= E1000_EECD_CS;
224 		wr32(E1000_EECD, eecd);
225 		wrfl();
226 		udelay(nvm->delay_usec);
227 		eecd &= ~E1000_EECD_CS;
228 		wr32(E1000_EECD, eecd);
229 		wrfl();
230 		udelay(nvm->delay_usec);
231 	}
232 }
233 
234 /**
235  *  e1000_stop_nvm - Terminate EEPROM command
236  *  @hw: pointer to the HW structure
237  *
238  *  Terminates the current command by inverting the EEPROM's chip select pin.
239  **/
240 static void e1000_stop_nvm(struct e1000_hw *hw)
241 {
242 	u32 eecd;
243 
244 	eecd = rd32(E1000_EECD);
245 	if (hw->nvm.type == e1000_nvm_eeprom_spi) {
246 		/* Pull CS high */
247 		eecd |= E1000_EECD_CS;
248 		igb_lower_eec_clk(hw, &eecd);
249 	}
250 }
251 
252 /**
253  *  igb_release_nvm - Release exclusive access to EEPROM
254  *  @hw: pointer to the HW structure
255  *
256  *  Stop any current commands to the EEPROM and clear the EEPROM request bit.
257  **/
258 void igb_release_nvm(struct e1000_hw *hw)
259 {
260 	u32 eecd;
261 
262 	e1000_stop_nvm(hw);
263 
264 	eecd = rd32(E1000_EECD);
265 	eecd &= ~E1000_EECD_REQ;
266 	wr32(E1000_EECD, eecd);
267 }
268 
269 /**
270  *  igb_ready_nvm_eeprom - Prepares EEPROM for read/write
271  *  @hw: pointer to the HW structure
272  *
273  *  Setups the EEPROM for reading and writing.
274  **/
275 static s32 igb_ready_nvm_eeprom(struct e1000_hw *hw)
276 {
277 	struct e1000_nvm_info *nvm = &hw->nvm;
278 	u32 eecd = rd32(E1000_EECD);
279 	s32 ret_val = 0;
280 	u16 timeout = 0;
281 	u8 spi_stat_reg;
282 
283 
284 	if (nvm->type == e1000_nvm_eeprom_spi) {
285 		/* Clear SK and CS */
286 		eecd &= ~(E1000_EECD_CS | E1000_EECD_SK);
287 		wr32(E1000_EECD, eecd);
288 		wrfl();
289 		udelay(1);
290 		timeout = NVM_MAX_RETRY_SPI;
291 
292 		/*
293 		 * Read "Status Register" repeatedly until the LSB is cleared.
294 		 * The EEPROM will signal that the command has been completed
295 		 * by clearing bit 0 of the internal status register.  If it's
296 		 * not cleared within 'timeout', then error out.
297 		 */
298 		while (timeout) {
299 			igb_shift_out_eec_bits(hw, NVM_RDSR_OPCODE_SPI,
300 						 hw->nvm.opcode_bits);
301 			spi_stat_reg = (u8)igb_shift_in_eec_bits(hw, 8);
302 			if (!(spi_stat_reg & NVM_STATUS_RDY_SPI))
303 				break;
304 
305 			udelay(5);
306 			igb_standby_nvm(hw);
307 			timeout--;
308 		}
309 
310 		if (!timeout) {
311 			hw_dbg("SPI NVM Status error\n");
312 			ret_val = -E1000_ERR_NVM;
313 			goto out;
314 		}
315 	}
316 
317 out:
318 	return ret_val;
319 }
320 
321 /**
322  *  igb_read_nvm_spi - Read EEPROM's using SPI
323  *  @hw: pointer to the HW structure
324  *  @offset: offset of word in the EEPROM to read
325  *  @words: number of words to read
326  *  @data: word read from the EEPROM
327  *
328  *  Reads a 16 bit word from the EEPROM.
329  **/
330 s32 igb_read_nvm_spi(struct e1000_hw *hw, u16 offset, u16 words, u16 *data)
331 {
332 	struct e1000_nvm_info *nvm = &hw->nvm;
333 	u32 i = 0;
334 	s32 ret_val;
335 	u16 word_in;
336 	u8 read_opcode = NVM_READ_OPCODE_SPI;
337 
338 	/*
339 	 * A check for invalid values:  offset too large, too many words,
340 	 * and not enough words.
341 	 */
342 	if ((offset >= nvm->word_size) || (words > (nvm->word_size - offset)) ||
343 	    (words == 0)) {
344 		hw_dbg("nvm parameter(s) out of bounds\n");
345 		ret_val = -E1000_ERR_NVM;
346 		goto out;
347 	}
348 
349 	ret_val = nvm->ops.acquire(hw);
350 	if (ret_val)
351 		goto out;
352 
353 	ret_val = igb_ready_nvm_eeprom(hw);
354 	if (ret_val)
355 		goto release;
356 
357 	igb_standby_nvm(hw);
358 
359 	if ((nvm->address_bits == 8) && (offset >= 128))
360 		read_opcode |= NVM_A8_OPCODE_SPI;
361 
362 	/* Send the READ command (opcode + addr) */
363 	igb_shift_out_eec_bits(hw, read_opcode, nvm->opcode_bits);
364 	igb_shift_out_eec_bits(hw, (u16)(offset*2), nvm->address_bits);
365 
366 	/*
367 	 * Read the data.  SPI NVMs increment the address with each byte
368 	 * read and will roll over if reading beyond the end.  This allows
369 	 * us to read the whole NVM from any offset
370 	 */
371 	for (i = 0; i < words; i++) {
372 		word_in = igb_shift_in_eec_bits(hw, 16);
373 		data[i] = (word_in >> 8) | (word_in << 8);
374 	}
375 
376 release:
377 	nvm->ops.release(hw);
378 
379 out:
380 	return ret_val;
381 }
382 
383 /**
384  *  igb_read_nvm_eerd - Reads EEPROM using EERD register
385  *  @hw: pointer to the HW structure
386  *  @offset: offset of word in the EEPROM to read
387  *  @words: number of words to read
388  *  @data: word read from the EEPROM
389  *
390  *  Reads a 16 bit word from the EEPROM using the EERD register.
391  **/
392 s32 igb_read_nvm_eerd(struct e1000_hw *hw, u16 offset, u16 words, u16 *data)
393 {
394 	struct e1000_nvm_info *nvm = &hw->nvm;
395 	u32 i, eerd = 0;
396 	s32 ret_val = 0;
397 
398 	/*
399 	 * A check for invalid values:  offset too large, too many words,
400 	 * and not enough words.
401 	 */
402 	if ((offset >= nvm->word_size) || (words > (nvm->word_size - offset)) ||
403 	    (words == 0)) {
404 		hw_dbg("nvm parameter(s) out of bounds\n");
405 		ret_val = -E1000_ERR_NVM;
406 		goto out;
407 	}
408 
409 	for (i = 0; i < words; i++) {
410 		eerd = ((offset+i) << E1000_NVM_RW_ADDR_SHIFT) +
411 		       E1000_NVM_RW_REG_START;
412 
413 		wr32(E1000_EERD, eerd);
414 		ret_val = igb_poll_eerd_eewr_done(hw, E1000_NVM_POLL_READ);
415 		if (ret_val)
416 			break;
417 
418 		data[i] = (rd32(E1000_EERD) >>
419 			E1000_NVM_RW_REG_DATA);
420 	}
421 
422 out:
423 	return ret_val;
424 }
425 
426 /**
427  *  igb_write_nvm_spi - Write to EEPROM using SPI
428  *  @hw: pointer to the HW structure
429  *  @offset: offset within the EEPROM to be written to
430  *  @words: number of words to write
431  *  @data: 16 bit word(s) to be written to the EEPROM
432  *
433  *  Writes data to EEPROM at offset using SPI interface.
434  *
435  *  If e1000_update_nvm_checksum is not called after this function , the
436  *  EEPROM will most likley contain an invalid checksum.
437  **/
438 s32 igb_write_nvm_spi(struct e1000_hw *hw, u16 offset, u16 words, u16 *data)
439 {
440 	struct e1000_nvm_info *nvm = &hw->nvm;
441 	s32 ret_val;
442 	u16 widx = 0;
443 
444 	/*
445 	 * A check for invalid values:  offset too large, too many words,
446 	 * and not enough words.
447 	 */
448 	if ((offset >= nvm->word_size) || (words > (nvm->word_size - offset)) ||
449 	    (words == 0)) {
450 		hw_dbg("nvm parameter(s) out of bounds\n");
451 		ret_val = -E1000_ERR_NVM;
452 		goto out;
453 	}
454 
455 	ret_val = hw->nvm.ops.acquire(hw);
456 	if (ret_val)
457 		goto out;
458 
459 	msleep(10);
460 
461 	while (widx < words) {
462 		u8 write_opcode = NVM_WRITE_OPCODE_SPI;
463 
464 		ret_val = igb_ready_nvm_eeprom(hw);
465 		if (ret_val)
466 			goto release;
467 
468 		igb_standby_nvm(hw);
469 
470 		/* Send the WRITE ENABLE command (8 bit opcode) */
471 		igb_shift_out_eec_bits(hw, NVM_WREN_OPCODE_SPI,
472 					 nvm->opcode_bits);
473 
474 		igb_standby_nvm(hw);
475 
476 		/*
477 		 * Some SPI eeproms use the 8th address bit embedded in the
478 		 * opcode
479 		 */
480 		if ((nvm->address_bits == 8) && (offset >= 128))
481 			write_opcode |= NVM_A8_OPCODE_SPI;
482 
483 		/* Send the Write command (8-bit opcode + addr) */
484 		igb_shift_out_eec_bits(hw, write_opcode, nvm->opcode_bits);
485 		igb_shift_out_eec_bits(hw, (u16)((offset + widx) * 2),
486 					 nvm->address_bits);
487 
488 		/* Loop to allow for up to whole page write of eeprom */
489 		while (widx < words) {
490 			u16 word_out = data[widx];
491 			word_out = (word_out >> 8) | (word_out << 8);
492 			igb_shift_out_eec_bits(hw, word_out, 16);
493 			widx++;
494 
495 			if ((((offset + widx) * 2) % nvm->page_size) == 0) {
496 				igb_standby_nvm(hw);
497 				break;
498 			}
499 		}
500 	}
501 
502 	msleep(10);
503 release:
504 	hw->nvm.ops.release(hw);
505 
506 out:
507 	return ret_val;
508 }
509 
510 /**
511  *  igb_read_part_string - Read device part number
512  *  @hw: pointer to the HW structure
513  *  @part_num: pointer to device part number
514  *  @part_num_size: size of part number buffer
515  *
516  *  Reads the product board assembly (PBA) number from the EEPROM and stores
517  *  the value in part_num.
518  **/
519 s32 igb_read_part_string(struct e1000_hw *hw, u8 *part_num, u32 part_num_size)
520 {
521 	s32 ret_val;
522 	u16 nvm_data;
523 	u16 pointer;
524 	u16 offset;
525 	u16 length;
526 
527 	if (part_num == NULL) {
528 		hw_dbg("PBA string buffer was null\n");
529 		ret_val = E1000_ERR_INVALID_ARGUMENT;
530 		goto out;
531 	}
532 
533 	ret_val = hw->nvm.ops.read(hw, NVM_PBA_OFFSET_0, 1, &nvm_data);
534 	if (ret_val) {
535 		hw_dbg("NVM Read Error\n");
536 		goto out;
537 	}
538 
539 	ret_val = hw->nvm.ops.read(hw, NVM_PBA_OFFSET_1, 1, &pointer);
540 	if (ret_val) {
541 		hw_dbg("NVM Read Error\n");
542 		goto out;
543 	}
544 
545 	/*
546 	 * if nvm_data is not ptr guard the PBA must be in legacy format which
547 	 * means pointer is actually our second data word for the PBA number
548 	 * and we can decode it into an ascii string
549 	 */
550 	if (nvm_data != NVM_PBA_PTR_GUARD) {
551 		hw_dbg("NVM PBA number is not stored as string\n");
552 
553 		/* we will need 11 characters to store the PBA */
554 		if (part_num_size < 11) {
555 			hw_dbg("PBA string buffer too small\n");
556 			return E1000_ERR_NO_SPACE;
557 		}
558 
559 		/* extract hex string from data and pointer */
560 		part_num[0] = (nvm_data >> 12) & 0xF;
561 		part_num[1] = (nvm_data >> 8) & 0xF;
562 		part_num[2] = (nvm_data >> 4) & 0xF;
563 		part_num[3] = nvm_data & 0xF;
564 		part_num[4] = (pointer >> 12) & 0xF;
565 		part_num[5] = (pointer >> 8) & 0xF;
566 		part_num[6] = '-';
567 		part_num[7] = 0;
568 		part_num[8] = (pointer >> 4) & 0xF;
569 		part_num[9] = pointer & 0xF;
570 
571 		/* put a null character on the end of our string */
572 		part_num[10] = '\0';
573 
574 		/* switch all the data but the '-' to hex char */
575 		for (offset = 0; offset < 10; offset++) {
576 			if (part_num[offset] < 0xA)
577 				part_num[offset] += '0';
578 			else if (part_num[offset] < 0x10)
579 				part_num[offset] += 'A' - 0xA;
580 		}
581 
582 		goto out;
583 	}
584 
585 	ret_val = hw->nvm.ops.read(hw, pointer, 1, &length);
586 	if (ret_val) {
587 		hw_dbg("NVM Read Error\n");
588 		goto out;
589 	}
590 
591 	if (length == 0xFFFF || length == 0) {
592 		hw_dbg("NVM PBA number section invalid length\n");
593 		ret_val = E1000_ERR_NVM_PBA_SECTION;
594 		goto out;
595 	}
596 	/* check if part_num buffer is big enough */
597 	if (part_num_size < (((u32)length * 2) - 1)) {
598 		hw_dbg("PBA string buffer too small\n");
599 		ret_val = E1000_ERR_NO_SPACE;
600 		goto out;
601 	}
602 
603 	/* trim pba length from start of string */
604 	pointer++;
605 	length--;
606 
607 	for (offset = 0; offset < length; offset++) {
608 		ret_val = hw->nvm.ops.read(hw, pointer + offset, 1, &nvm_data);
609 		if (ret_val) {
610 			hw_dbg("NVM Read Error\n");
611 			goto out;
612 		}
613 		part_num[offset * 2] = (u8)(nvm_data >> 8);
614 		part_num[(offset * 2) + 1] = (u8)(nvm_data & 0xFF);
615 	}
616 	part_num[offset * 2] = '\0';
617 
618 out:
619 	return ret_val;
620 }
621 
622 /**
623  *  igb_read_mac_addr - Read device MAC address
624  *  @hw: pointer to the HW structure
625  *
626  *  Reads the device MAC address from the EEPROM and stores the value.
627  *  Since devices with two ports use the same EEPROM, we increment the
628  *  last bit in the MAC address for the second port.
629  **/
630 s32 igb_read_mac_addr(struct e1000_hw *hw)
631 {
632 	u32 rar_high;
633 	u32 rar_low;
634 	u16 i;
635 
636 	rar_high = rd32(E1000_RAH(0));
637 	rar_low = rd32(E1000_RAL(0));
638 
639 	for (i = 0; i < E1000_RAL_MAC_ADDR_LEN; i++)
640 		hw->mac.perm_addr[i] = (u8)(rar_low >> (i*8));
641 
642 	for (i = 0; i < E1000_RAH_MAC_ADDR_LEN; i++)
643 		hw->mac.perm_addr[i+4] = (u8)(rar_high >> (i*8));
644 
645 	for (i = 0; i < ETH_ALEN; i++)
646 		hw->mac.addr[i] = hw->mac.perm_addr[i];
647 
648 	return 0;
649 }
650 
651 /**
652  *  igb_validate_nvm_checksum - Validate EEPROM checksum
653  *  @hw: pointer to the HW structure
654  *
655  *  Calculates the EEPROM checksum by reading/adding each word of the EEPROM
656  *  and then verifies that the sum of the EEPROM is equal to 0xBABA.
657  **/
658 s32 igb_validate_nvm_checksum(struct e1000_hw *hw)
659 {
660 	s32 ret_val = 0;
661 	u16 checksum = 0;
662 	u16 i, nvm_data;
663 
664 	for (i = 0; i < (NVM_CHECKSUM_REG + 1); i++) {
665 		ret_val = hw->nvm.ops.read(hw, i, 1, &nvm_data);
666 		if (ret_val) {
667 			hw_dbg("NVM Read Error\n");
668 			goto out;
669 		}
670 		checksum += nvm_data;
671 	}
672 
673 	if (checksum != (u16) NVM_SUM) {
674 		hw_dbg("NVM Checksum Invalid\n");
675 		ret_val = -E1000_ERR_NVM;
676 		goto out;
677 	}
678 
679 out:
680 	return ret_val;
681 }
682 
683 /**
684  *  igb_update_nvm_checksum - Update EEPROM checksum
685  *  @hw: pointer to the HW structure
686  *
687  *  Updates the EEPROM checksum by reading/adding each word of the EEPROM
688  *  up to the checksum.  Then calculates the EEPROM checksum and writes the
689  *  value to the EEPROM.
690  **/
691 s32 igb_update_nvm_checksum(struct e1000_hw *hw)
692 {
693 	s32  ret_val;
694 	u16 checksum = 0;
695 	u16 i, nvm_data;
696 
697 	for (i = 0; i < NVM_CHECKSUM_REG; i++) {
698 		ret_val = hw->nvm.ops.read(hw, i, 1, &nvm_data);
699 		if (ret_val) {
700 			hw_dbg("NVM Read Error while updating checksum.\n");
701 			goto out;
702 		}
703 		checksum += nvm_data;
704 	}
705 	checksum = (u16) NVM_SUM - checksum;
706 	ret_val = hw->nvm.ops.write(hw, NVM_CHECKSUM_REG, 1, &checksum);
707 	if (ret_val)
708 		hw_dbg("NVM Write Error while updating checksum.\n");
709 
710 out:
711 	return ret_val;
712 }
713