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@xxxxxxxxxxxxxxx # 5.15+
Reported-and-tested-by: Stan Johnson <userm57@xxxxxxxxx>
Fixes: 7c1f3e3447a1 ("scsi: mac_scsi: Treat Last Byte Sent time-out as failure")
Signed-off-by: Finn Thain <fthain@xxxxxxxxxxxxxx>
---
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,
--
2.39.5
