Since v2.6.35 commit 683229845f17 ("[SCSI] zfcp: Report scatter-gather
limits to SCSI and block layer"), zfcp set dma_parms.max_segment_size ==
PAGE_SIZE (but without using the setter dma_set_max_seg_size())
and scsi_host_template.dma_boundary == PAGE_SIZE - 1.
v5.0-rc1 commit 50c2e9107f17 ("scsi: introduce a max_segment_size
host_template parameters") introduced a new field
scsi_host_template.max_segment_size. If an LLDD such as zfcp does not set
it, scsi_host_alloc() uses BLK_MAX_SEGMENT_SIZE = 65536 for
Scsi_Host.max_segment_size. __scsi_init_queue() announced the minimum
of Scsi_Host.max_segment_size and dma_parms.max_segment_size to the block
layer. For zfcp: min(65536, 4096) == 4096 which was still good.
v5.0 commit a8cf59a6692c ("scsi: communicate max segment size to the DMA
mapping code") announces Scsi_Host.max_segment_size to the block layer
and overwrites dma_parms.max_segment_size with Scsi_Host.max_segment_size.
For zfcp dma_parms.max_segment_size == Scsi_Host.max_segment_size == 65536
which is also reflected in block queue limits.
$ cd /sys/bus/ccw/drivers/zfcp
$ cd 0.0.3c40/host5/rport-5:0-4/target5:0:4/5:0:4:10/block/sdi/queue
$ cat max_segment_size
65536
Zfcp I/O still works because dma_boundary implicitly still keeps the
effective max segment size <= PAGE_SIZE.
However, dma_boundary does not seem visible to user space,
but max_segment_size is visible and shows a misleading wrong value.
Fix it and inherit the stable tag of a8cf59a6692c.
Devices on our bus ccw support DMA but no DMA mapping. Of multiple device
types on the ccw bus, only zfcp needs dma_parms for SCSI limits.
So, leave dma_parms setup in zfcp and do not move it to the bus.
Signed-off-by: Steffen Maier <maier@xxxxxxxxxxxxx>
Fixes: 50c2e9107f ("scsi: introduce a max_segment_size host_template parameters")
---
Martin, James, this would be for 5.0/scsi-fixes.
drivers/s390/scsi/zfcp_aux.c | 1 -
drivers/s390/scsi/zfcp_scsi.c | 2 ++
2 files changed, 2 insertions(+), 1 deletion(-)
diff --git a/drivers/s390/scsi/zfcp_aux.c b/drivers/s390/scsi/zfcp_aux.c
index 9cf30d124b9e..e390f8c6d5f3 100644
--- a/drivers/s390/scsi/zfcp_aux.c
+++ b/drivers/s390/scsi/zfcp_aux.c
@@ -403,7 +403,6 @@ struct zfcp_adapter *zfcp_adapter_enqueue(struct ccw_device *ccw_device)
goto failed;
/* report size limit per scatter-gather segment */
- adapter->dma_parms.max_segment_size = ZFCP_QDIO_SBALE_LEN;
adapter->ccw_device->dev.dma_parms = &adapter->dma_parms;
adapter->stat_read_buf_num = FSF_STATUS_READS_RECOM;
diff --git a/drivers/s390/scsi/zfcp_scsi.c b/drivers/s390/scsi/zfcp_scsi.c
index 00acc7144bbc..f4f6a07c5222 100644
--- a/drivers/s390/scsi/zfcp_scsi.c
+++ b/drivers/s390/scsi/zfcp_scsi.c
@@ -428,6 +428,8 @@ static struct scsi_host_template zfcp_scsi_host_template = {
.max_sectors = (((QDIO_MAX_ELEMENTS_PER_BUFFER - 1)
* ZFCP_QDIO_MAX_SBALS_PER_REQ) - 2) * 8,
/* GCD, adjusted later */
+ /* report size limit per scatter-gather segment */
+ .max_segment_size = ZFCP_QDIO_SBALE_LEN,
.dma_boundary = ZFCP_QDIO_SBALE_LEN - 1,
.shost_attrs = zfcp_sysfs_shost_attrs,
.sdev_attrs = zfcp_sysfs_sdev_attrs,
--
2.16.4
