libata: eliminate the home grown dma padding in favour of

that provided by the block layer

ATA requires that all DMA transfers begin and end on word boundaries.
Because of this, a large amount of machinery grew up in ide to adjust
scatterlists on this basis.  However, as of 2.5, the block layer has a
dma_alignment variable which ensures both the beginning and length of a
DMA transfer are aligned on the dma_alignment boundary.  Although the
block layer does adjust the beginning of the transfer to ensure this
happens, it doesn't actually adjust the length, it merely makes sure
that space is allocated for transfers beyond the declared length.  The
upshot of this is that scatterlists may be padded to any size between
the actual length and the length adjusted to the dma_alignment safely
knowing that memory is allocated in this region.

Right at the moment, SCSI takes the default dma_aligment which is on a
512 byte boundary.  Note that this aligment only applies to transfers
coming in from user space.  However, since all kernel allocations are
automatically aligned on a minimum of 32 byte boundaries, it is safe to
adjust them in this manner as well.

tj: * Adjusting sg after padding is done in block layer.  Make libata
      set queue alignment correctly for ATAPI devices and drop broken
      sg mangling from ata_sg_setup().
    * Use request->raw_data_len for ATAPI transfer chunk size.
    * Killed qc->raw_nbytes.
    * Separated out killing qc->n_iter.

Signed-off-by: James Bottomley <James.Bottomley@HansenPartnership.com>
Signed-off-by: Tejun Heo <htejun@gmail.com>
Signed-off-by: Jens Axboe <jens.axboe@oracle.com>

1 files changed, 1 insertions, 27 deletions

diff --git a/include/linux/libata.h b/include/linux/libata.h
index bc5a8d0c7090..2e098f940cec 100644
--- a/include/linux/libata.h
+++ b/include/linux/libata.h
@@ -278,7 +278,6 @@ enum {
 
         /* size of buffer to pad xfers ending on unaligned boundaries */
         ATA_DMA_PAD_SZ          = 4,
-        ATA_DMA_PAD_BUF_SZ      = ATA_DMA_PAD_SZ * ATA_MAX_QUEUE,
 
         /* ering size */
         ATA_ERING_SIZE          = 32,
@@ -457,24 +456,18 @@ struct ata_queued_cmd {
         unsigned long           flags;          /* ATA_QCFLAG_xxx */
         unsigned int            tag;
         unsigned int            n_elem;
-        unsigned int            mapped_n_elem;
 
         int                     dma_dir;
 
-        unsigned int            pad_len;
         unsigned int            sect_size;
 
         unsigned int            nbytes;
-        unsigned int            raw_nbytes;
         unsigned int            curbytes;
 
         struct scatterlist      *cursg;
         unsigned int            cursg_ofs;
 
-        struct scatterlist      *last_sg;
-        struct scatterlist      saved_last_sg;
         struct scatterlist      sgent;
-        struct scatterlist      extra_sg[2];
 
         struct scatterlist      *sg;
 
@@ -619,9 +612,6 @@ struct ata_port {
         struct ata_prd          *prd;    /* our SG list */
         dma_addr_t              prd_dma; /* and its DMA mapping */
 
-        void                    *pad;   /* array of DMA pad buffers */
-        dma_addr_t              pad_dma;
-
         struct ata_ioports      ioaddr; /* ATA cmd/ctl/dma register blocks */
 
         u8                      ctl;    /* cache of ATA control register */
@@ -1363,12 +1353,9 @@ static inline void ata_qc_reinit(struct ata_queued_cmd *qc)
         qc->flags = 0;
         qc->cursg = NULL;
         qc->cursg_ofs = 0;
-        qc->nbytes = qc->raw_nbytes = qc->curbytes = 0;
+        qc->nbytes = qc->curbytes = 0;
         qc->n_elem = 0;
-        qc->mapped_n_elem = 0;
         qc->err_mask = 0;
-        qc->pad_len = 0;
-        qc->last_sg = NULL;
         qc->sect_size = ATA_SECT_SIZE;
 
         ata_tf_init(qc->dev, &qc->tf);
@@ -1423,19 +1410,6 @@ static inline unsigned int __ac_err_mask(u8 status)
         return mask;
 }
 
-static inline int ata_pad_alloc(struct ata_port *ap, struct device *dev)
-{
-        ap->pad_dma = 0;
-        ap->pad = dmam_alloc_coherent(dev, ATA_DMA_PAD_BUF_SZ,
-                                      &ap->pad_dma, GFP_KERNEL);
-        return (ap->pad == NULL) ? -ENOMEM : 0;
-}
-
-static inline void ata_pad_free(struct ata_port *ap, struct device *dev)
-{
-        dmam_free_coherent(dev, ATA_DMA_PAD_BUF_SZ, ap->pad, ap->pad_dma);
-}
-
 static inline struct ata_port *ata_shost_to_port(struct Scsi_Host *host)
 {
         return *(struct ata_port **)&host->hostdata[0];