SD cards can produce write latency spikes on the order of a hundred milliseconds. If the target firmware does not hide that latency during DATA IN and OUT phases it can cause the PDMA circuitry to raise a processor bus fault which in turn leads to an unreliable byte count and a DMA overrun.
The Last Byte Sent flag is used to detect the overrun but this mechanism is unreliable on some systems. Instead, set a DID_ERROR result whenever there is a bus fault during a PDMA send, unless the cause was a phase mismatch.
Cc: stable@vger.kernel.org # 5.15+ Reported-and-tested-by: Stan Johnson userm57@yahoo.com Fixes: 7c1f3e3447a1 ("scsi: mac_scsi: Treat Last Byte Sent time-out as failure") Signed-off-by: Finn Thain fthain@linux-m68k.org --- drivers/scsi/mac_scsi.c | 44 ++++++++++++++++++----------------------- 1 file changed, 19 insertions(+), 25 deletions(-)
diff --git a/drivers/scsi/mac_scsi.c b/drivers/scsi/mac_scsi.c index 39814c841113..2e9fad1e3069 100644 --- a/drivers/scsi/mac_scsi.c +++ b/drivers/scsi/mac_scsi.c @@ -102,11 +102,15 @@ __setup("mac5380=", mac_scsi_setup); * Linux SCSI drivers lack knowledge of the timing behaviour of SCSI targets * so bus errors are unavoidable. * - * If a MOVE.B instruction faults, we assume that zero bytes were transferred - * and simply retry. That assumption probably depends on target behaviour but - * seems to hold up okay. The NOP provides synchronization: without it the - * fault can sometimes occur after the program counter has moved past the - * offending instruction. Post-increment addressing can't be used. + * If a MOVE.B instruction faults during a receive operation, we assume the + * target sent nothing and try again. That assumption probably depends on + * target firmware but it seems to hold up okay. If a fault happens during a + * send operation, the target may or may not have seen /ACK and got the byte. + * It's uncertain so the whole SCSI command gets retried. + * + * The NOP is needed for synchronization because the fault address in the + * exception stack frame may or may not be the instruction that actually + * caused the bus error. Post-increment addressing can't be used. */
#define MOVE_BYTE(operands) \ @@ -243,22 +247,21 @@ static inline int mac_pdma_send(unsigned char *start, void __iomem *io, int n) if (n >= 1) { MOVE_BYTE("%0@,%3@"); if (result) - goto out; + return -1; } if (n >= 1 && ((unsigned long)addr & 1)) { MOVE_BYTE("%0@,%3@"); if (result) - goto out; + return -2; } while (n >= 32) MOVE_16_WORDS("%0@+,%3@"); while (n >= 2) MOVE_WORD("%0@+,%3@"); if (result) - return start - addr; /* Negated to indicate uncertain length */ + return start - addr - 1; /* Negated to indicate uncertain length */ if (n == 1) MOVE_BYTE("%0@,%3@"); -out: return addr - start; }
@@ -307,7 +310,6 @@ static inline int macscsi_pread(struct NCR5380_hostdata *hostdata, { u8 __iomem *s = hostdata->pdma_io + (INPUT_DATA_REG << 4); unsigned char *d = dst; - int result = 0;
hostdata->pdma_residual = len;
@@ -343,11 +345,12 @@ static inline int macscsi_pread(struct NCR5380_hostdata *hostdata, if (bytes == 0) continue;
- result = -1; + if (macscsi_wait_for_drq(hostdata) <= 0) + set_host_byte(hostdata->connected, DID_ERROR); break; }
- return result; + return 0; }
static inline int macscsi_pwrite(struct NCR5380_hostdata *hostdata, @@ -355,7 +358,6 @@ static inline int macscsi_pwrite(struct NCR5380_hostdata *hostdata, { unsigned char *s = src; u8 __iomem *d = hostdata->pdma_io + (OUTPUT_DATA_REG << 4); - int result = 0;
hostdata->pdma_residual = len;
@@ -377,17 +379,8 @@ static inline int macscsi_pwrite(struct NCR5380_hostdata *hostdata, hostdata->pdma_residual -= bytes; }
- if (hostdata->pdma_residual == 0) { - if (NCR5380_poll_politely(hostdata, TARGET_COMMAND_REG, - TCR_LAST_BYTE_SENT, - TCR_LAST_BYTE_SENT, - 0) < 0) { - scmd_printk(KERN_ERR, hostdata->connected, - "%s: Last Byte Sent timeout\n", __func__); - result = -1; - } + if (hostdata->pdma_residual == 0) break; - }
if (bytes > 0) continue; @@ -400,11 +393,12 @@ static inline int macscsi_pwrite(struct NCR5380_hostdata *hostdata, if (bytes == 0) continue;
- result = -1; + if (macscsi_wait_for_drq(hostdata) <= 0) + set_host_byte(hostdata->connected, DID_ERROR); break; }
- return result; + return 0; }
static int macscsi_dma_xfer_len(struct NCR5380_hostdata *hostdata,