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scsi: mac_scsi: Disallow bus errors during PDMA send

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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: 7c1f3e3447 ("scsi: mac_scsi: Treat Last Byte Sent time-out as failure")
Signed-off-by: Finn Thain <fthain@linux-m68k.org>
Link: https://lore.kernel.org/r/cc38df687ace2c4ffc375a683b2502fc476b600d.1723001788.git.fthain@linux-m68k.org
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
This commit is contained in:
Finn Thain 2024-08-07 13:36:28 +10:00 committed by Martin K. Petersen
parent 5545c3165c
commit 5551bc30e4
1 changed files with 19 additions and 25 deletions
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44
drivers/scsi/mac_scsi.c
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@ -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,