LS2085ARDB data cache corruption

yanyan · ‎02-14-2016

we encountered data corruption issues after D-cache disable/enable cycle on LS2085ARDB board, the code sequence is:

1. disable the global Data/Unify cache by clearing SCTLR.C bit;

2. do cache clean by way/set as recommended by ARM user manual;

3. modify data when cache disabled;

4. re-enable Data/Unify cache by setting SCTRL.C bit;

5. the modified data in step 3 is not visible any more.

This issue is observed in both AARCH64 and AARCH32 modes. We created a small testcase as shown below; this testcase is loaded by u-boot. a brief explanation of the test code:

1. the testcase is loaded to address 0x80100000, and from the u-boot shell, 'go 0x80100000' to enter the testcase.

2. the testcase just replicates the above described sequence, first, it writes constant #1 to address 0x80000000, then disable and clean the cache, and write constant #2 to 0x80000000, after that, enable the cache again, and try reading from 0x80000000; if the read value is #2, then the modification is visible and test passed ('A' is printed on console), otherwise 'B' is printed. Please note the testcase inherits the MMU & page attributes settings from the LS2085ARDB u-boot, which is cacheable writeback for address at 0x80000000.

=======================================

Test code:

retry:

LDR x0, =0x80000000

MOV x1, #1

STR x1, [x0]

/********************************************clean all ****************/

DMB SY

MRS X0, CLIDR_EL1

AND W3, W0, #CLIDR_LOC

LSR W3, W3, #(CLIDR_LOC_SHIFT - 1) /* get 2x LoC */

CBZ W3, 5f /* done */

MOV W10, #0 /* W10 = 2x LoC */

MOV W8, #1 /* W8 = constant 0b1 */

1:

ADD W2, W10, W10, LSR #1 /* W2 = 3x LoC */

LSR W1, W0, W2

AND W1, W1, #CLIDR_CTYPE_MASK /* get cache type */

CMP W1, #CLIDR_CTYPE_D

B.LT 4f /* skip if no or i-cache */

MRS X14, DAIF

MSR DAIFSet, #3

MSR CSSELR_EL1, X10 /* select this cache */

ISB /* Synchronize change of CSSELR */

MRS X1, CCSIDR_EL1 /* read CCSIDR */

MSR DAIF, X14

AND W2, W1, #CCSIDR_LINESIZE_MASK /* W2 = log2(linelen)-4 */

ADD W2, W2, #4 /* W2 = log2(linelen) */

UBFX W4, W1, #3, #10 /* W4 = max way number/associativity */

CLZ W5, W4 /* W5 = 32-log2(ways), bit position of way in DC operand */

LSL W9, W4, W5 /* W9 = max way number, aligned to position in DC operand */

LSL W12, W8, W5 /* W12 = amount to decrement way number per iteration */

2:

UBFX W7, W1, #13, #15 /* W7 = max set number, right aligned */

LSL W7, W7, W2 /* W7 = max set number, aligned to position in DC operand */

LSL W13, W8, W2 /* W13 = amount to decrement set number per iteration */

3:

ORR W11, W10, W9 /* W11 = combine way number and cache number */

ORR W11, W11, W7 /* and set number for DC operand */

DC CISW, X11 /* Do data cache operation by set and way */

SUBS W7, W7, W13 /* Decrement set number */

B.GE 3b

SUBS X9, X9, X12 /* Decrement way number */

B.GE 2b

4:

ADD W10, W10, #2 /* Increment 2 x cache level */

CMP W3, W10

DSB SY

B.GT 1b

5:

MOV X10, #0 // swith back to cache level 0

MSR CSSELR_EL1, X10 // select current cache level in csselr

DSB SY

ISB

/********************************************clean done **************/

MRS X0, SCTLR_EL3

BIC X0, X0, SCTLR_C /* disable D-Cache */

MSR SCTLR_EL3, X0

ISB SY /* Guarantees visibility to instruction fetch */

LDR x0, =0x80000000

MOV x1, #2

STR x1, [x0]

MRS X0, SCTLR_EL3

ORR X0, X0, #SCTLR_C /* enable d-cache*/

MSR SCTLR_EL3, X0

ISB SY /* Guarantees visibility to instruction fetch */

LDR x0, =0x80000000

LDR x1, [x0]

CMP x1, #2

BNE error

ok:

LDR x2, =0x21c0600

MOV x3, #65

STRB w3, [x2]

B retry

error:

CMP x1, #1

BNE 2f

LDR x2, =0x21c0600

MOV x3, #66

STRB w3, [x2]

B .

2:

LDR x2, =0x21c0600

MOV x3, #67

STRB w3, [x2]

B .

/* end */

Yuri · ‎03-01-2016

Hello,

Perhaps it makes sense to try the code under bare metal environment, without U-boot, which has own system initialization.

The L1 data memory system uses memory attributes from the MMU to determine the behaviors of memory transactions to regions of memory. Therefore the MMU should be properly configured and enabled to check data cache operations.

Have a great day,
Yuri

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