[libata] kill ata_sg_is_last()

Short term, this works around a bug introduced by early sg-chaining
work.

Long term, removing this function eliminates a branch from a hot
path loop in each scatter/gather table build.  Also, as this code
demonstrates, we don't need to _track_ the end of the s/g list, as
long as we mark it in some way.  And doing so programatically is nice.
So its a useful cleanup, regardless of its short term effects.

Based conceptually on a quick patch by Jens Axboe.

Signed-off-by: Jeff Garzik <jgarzik@redhat.com>

1 files changed, 7 insertions, 19 deletions

diff --git a/drivers/ata/sata_mv.c b/drivers/ata/sata_mv.c
index 4df8311968e9..7f1b13e89cf7 100644
--- a/drivers/ata/sata_mv.c
+++ b/drivers/ata/sata_mv.c
@@ -421,7 +421,6 @@ static void mv_error_handler(struct ata_port *ap);
 static void mv_post_int_cmd(struct ata_queued_cmd *qc);
 static void mv_eh_freeze(struct ata_port *ap);
 static void mv_eh_thaw(struct ata_port *ap);
-static int mv_slave_config(struct scsi_device *sdev);
 static int mv_init_one(struct pci_dev *pdev, const struct pci_device_id *ent);
 
 static void mv5_phy_errata(struct mv_host_priv *hpriv, void __iomem *mmio,
@@ -459,7 +458,7 @@ static struct scsi_host_template mv5_sht = {
         .use_clustering         = 1,
         .proc_name              = DRV_NAME,
         .dma_boundary           = MV_DMA_BOUNDARY,
-        .slave_configure        = mv_slave_config,
+        .slave_configure        = ata_scsi_slave_config,
         .slave_destroy          = ata_scsi_slave_destroy,
         .bios_param             = ata_std_bios_param,
 };
@@ -477,7 +476,7 @@ static struct scsi_host_template mv6_sht = {
         .use_clustering         = 1,
         .proc_name              = DRV_NAME,
         .dma_boundary           = MV_DMA_BOUNDARY,
-        .slave_configure        = mv_slave_config,
+        .slave_configure        = ata_scsi_slave_config,
         .slave_destroy          = ata_scsi_slave_destroy,
         .bios_param             = ata_std_bios_param,
 };
@@ -756,17 +755,6 @@ static void mv_irq_clear(struct ata_port *ap)
 {
 }
 
-static int mv_slave_config(struct scsi_device *sdev)
-{
-        int rc = ata_scsi_slave_config(sdev);
-        if (rc)
-                return rc;
-
-        blk_queue_max_phys_segments(sdev->request_queue, MV_MAX_SG_CT / 2);
-
-        return 0;       /* scsi layer doesn't check return value, sigh */
-}
-
 static void mv_set_edma_ptrs(void __iomem *port_mmio,
                              struct mv_host_priv *hpriv,
                              struct mv_port_priv *pp)
@@ -1138,7 +1126,7 @@ static void mv_fill_sg(struct ata_queued_cmd *qc)
 {
         struct mv_port_priv *pp = qc->ap->private_data;
         struct scatterlist *sg;
-        struct mv_sg *mv_sg;
+        struct mv_sg *mv_sg, *last_sg = NULL;
 
         mv_sg = pp->sg_tbl;
         ata_for_each_sg(sg, qc) {
@@ -1159,13 +1147,13 @@ static void mv_fill_sg(struct ata_queued_cmd *qc)
                         sg_len -= len;
                         addr += len;
 
-                        if (!sg_len && ata_sg_is_last(sg, qc))
-                                mv_sg->flags_size |= cpu_to_le32(EPRD_FLAG_END_OF_TBL);
-
+                        last_sg = mv_sg;
                         mv_sg++;
                 }
-
         }
+
+        if (likely(last_sg))
+                last_sg->flags_size |= cpu_to_le32(EPRD_FLAG_END_OF_TBL);
 }
 
 static inline void mv_crqb_pack_cmd(__le16 *cmdw, u8 data, u8 addr, unsigned last)