[PATCH v2] scsi: libsas: Reset num_scatter if libata mark qc as NODATA

[Jolly Shah <jollys@google.com>]

When the cache_type for the scsi device is changed, the scsi layer
issues a MODE_SELECT command. The caching mode details are communicated
via a request buffer associated with the scsi command with data
direction set as DMA_TO_DEVICE (scsi_mode_select). When this command
reaches the libata layer, as a part of generic initial setup, libata
layer sets up the scatterlist for the command using the scsi command
(ata_scsi_qc_new). This command is then translated by the libata layer
into ATA_CMD_SET_FEATURES (ata_scsi_mode_select_xlat). The libata layer
treats this as a non data command (ata_mselect_caching), since it only
needs an ata taskfile to pass the caching on/off information to the
device. It does not need the scatterlist that has been setup, so it does
not perform dma_map_sg on the scatterlist (ata_qc_issue). Unfortunately,
when this command reaches the libsas layer(sas_ata_qc_issue), libsas
layer sees it as a non data command with a scatterlist. It cannot
extract the correct dma length, since the scatterlist has not been
mapped with dma_map_sg for a DMA operation. When this partially
constructed SAS task reaches pm80xx LLDD, it results in below warning.

"pm80xx_chip_sata_req 6058: The sg list address
start_addr=0x0000000000000000 data_len=0x0end_addr_high=0xffffffff
end_addr_low=0xffffffff has crossed 4G boundary"

This patch updates code to handle ata non data commands separately so
num_scatter and total_xfer_len remain 0.

Fixes: 53de092f47ff ("scsi: libsas: Set data_dir as DMA_NONE if libata marks qc as NODATA")
Signed-off-by: Jolly Shah <jollys@google.com>
---
v2:
- reorganized code to avoid setting num_scatter twice

 drivers/scsi/libsas/sas_ata.c | 9 ++++-----
 1 file changed, 4 insertions(+), 5 deletions(-)

diff --git a/drivers/scsi/libsas/sas_ata.c b/drivers/scsi/libsas/sas_ata.c
index 024e5a550759..8b9a39077dba 100644
--- a/drivers/scsi/libsas/sas_ata.c
+++ b/drivers/scsi/libsas/sas_ata.c
@@ -201,18 +201,17 @@ static unsigned int sas_ata_qc_issue(struct ata_queued_cmd *qc)
 		memcpy(task->ata_task.atapi_packet, qc->cdb, qc->dev->cdb_len);
 		task->total_xfer_len = qc->nbytes;
 		task->num_scatter = qc->n_elem;
+		task->data_dir = qc->dma_dir;
+	} else if (qc->tf.protocol == ATA_PROT_NODATA) {
+		task->data_dir = DMA_NONE;
 	} else {
 		for_each_sg(qc->sg, sg, qc->n_elem, si)
 			xfer += sg_dma_len(sg);
 
 		task->total_xfer_len = xfer;
 		task->num_scatter = si;
-	}
-
-	if (qc->tf.protocol == ATA_PROT_NODATA)
-		task->data_dir = DMA_NONE;
-	else
 		task->data_dir = qc->dma_dir;
+	}
 	task->scatter = qc->sg;
 	task->ata_task.retry_count = 1;
 	task->task_state_flags = SAS_TASK_STATE_PENDING;
-- 
2.31.0.rc2.261.g7f71774620-goog