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Subject[PATCH] ata_sg_setup_one vs ata_sg_setup?
Date
Hi Jeff,

Was looking through libata, and it seems to me that ata_sg_setup is a
superset of ata_sg_setup_one. Am I missing something? Seems like it could
be simplified.

My machine never seems to do an ata_sg_setup_one, so this patch isn't really
tested...

Thanks,
Rusty.
---
Subject: libata: fold ata_queued_cmd single and sg logic
libata separates the single buffer case from the scatterlist case
internally. It's not clear that this is necessary.

Remove the ATA_QCFLAG_SINGLE flag, and buf_virt pointer, and always
initialize qc->nbytes in ata_sg_init().

It's possible that the ATA_QCFLAG_SG and ATA_QCFLAG_DMAMAP flags could
be entirely removed, and we could use whether qc->__sg is NULL or not.

Signed-off-by: Rusty Russell <rusty@rustcorp.com.au>

diff -r 8b1075c7ad47 drivers/ata/libata-core.c
--- a/drivers/ata/libata-core.c Tue Nov 13 21:00:47 2007 +1100
+++ b/drivers/ata/libata-core.c Wed Nov 14 15:31:07 2007 +1100
@@ -1648,16 +1648,8 @@ unsigned ata_exec_internal_sg(struct ata
memcpy(qc->cdb, cdb, ATAPI_CDB_LEN);
qc->flags |= ATA_QCFLAG_RESULT_TF;
qc->dma_dir = dma_dir;
- if (dma_dir != DMA_NONE) {
- unsigned int i, buflen = 0;
- struct scatterlist *sg;
-
- for_each_sg(sgl, sg, n_elem, i)
- buflen += sg->length;
-
+ if (dma_dir != DMA_NONE)
ata_sg_init(qc, sgl, n_elem);
- qc->nbytes = buflen;
- }

qc->private_data = &wait;
qc->complete_fn = ata_qc_complete_internal;
@@ -4543,9 +4535,6 @@ void ata_sg_clean(struct ata_queued_cmd
WARN_ON(!(qc->flags & ATA_QCFLAG_DMAMAP));
WARN_ON(sg == NULL);

- if (qc->flags & ATA_QCFLAG_SINGLE)
- WARN_ON(qc->n_elem > 1);
-
VPRINTK("unmapping %u sg elements\n", qc->n_elem);

/* if we padded the buffer out to 32-bit bound, and data
@@ -4566,16 +4555,6 @@ void ata_sg_clean(struct ata_queued_cmd
memcpy(addr + psg->offset, pad_buf, qc->pad_len);
kunmap_atomic(addr, KM_IRQ0);
}
- } else {
- if (qc->n_elem)
- dma_unmap_single(ap->dev,
- sg_dma_address(&sg[0]), sg_dma_len(&sg[0]),
- dir);
- /* restore sg */
- sg->length += qc->pad_len;
- if (pad_buf)
- memcpy(qc->buf_virt + sg->length - qc->pad_len,
- pad_buf, qc->pad_len);
}

qc->flags &= ~ATA_QCFLAG_DMAMAP;
@@ -4807,16 +4786,8 @@ void ata_noop_qc_prep(struct ata_queued_

void ata_sg_init_one(struct ata_queued_cmd *qc, void *buf, unsigned int buflen)
{
- qc->flags |= ATA_QCFLAG_SINGLE;
-
- qc->__sg = &qc->sgent;
- qc->n_elem = 1;
- qc->orig_n_elem = 1;
- qc->buf_virt = buf;
- qc->nbytes = buflen;
- qc->cursg = qc->__sg;
-
sg_init_one(&qc->sgent, buf, buflen);
+ ata_sg_init(qc, &qc->sgent, 1);
}

/**
@@ -4841,75 +4813,13 @@ void ata_sg_init(struct ata_queued_cmd *
qc->n_elem = n_elem;
qc->orig_n_elem = n_elem;
qc->cursg = qc->__sg;
-}
-
-/**
- * ata_sg_setup_one - DMA-map the memory buffer associated with a command.
- * @qc: Command with memory buffer to be mapped.
- *
- * DMA-map the memory buffer associated with queued_cmd @qc.
- *
- * LOCKING:
- * spin_lock_irqsave(host lock)
- *
- * RETURNS:
- * Zero on success, negative on error.
- */
-
-static int ata_sg_setup_one(struct ata_queued_cmd *qc)
-{
- struct ata_port *ap = qc->ap;
- int dir = qc->dma_dir;
- struct scatterlist *sg = qc->__sg;
- dma_addr_t dma_address;
- int trim_sg = 0;
-
- /* we must lengthen transfers to end on a 32-bit boundary */
- qc->pad_len = sg->length & 3;
- if (qc->pad_len) {
- void *pad_buf = ap->pad + (qc->tag * ATA_DMA_PAD_SZ);
- struct scatterlist *psg = &qc->pad_sgent;
-
- WARN_ON(qc->dev->class != ATA_DEV_ATAPI);
-
- memset(pad_buf, 0, ATA_DMA_PAD_SZ);
-
- if (qc->tf.flags & ATA_TFLAG_WRITE)
- memcpy(pad_buf, qc->buf_virt + sg->length - qc->pad_len,
- qc->pad_len);
-
- sg_dma_address(psg) = ap->pad_dma + (qc->tag * ATA_DMA_PAD_SZ);
- sg_dma_len(psg) = ATA_DMA_PAD_SZ;
- /* trim sg */
- sg->length -= qc->pad_len;
- if (sg->length == 0)
- trim_sg = 1;
-
- DPRINTK("padding done, sg->length=%u pad_len=%u\n",
- sg->length, qc->pad_len);
- }
-
- if (trim_sg) {
- qc->n_elem--;
- goto skip_map;
- }
-
- dma_address = dma_map_single(ap->dev, qc->buf_virt,
- sg->length, dir);
- if (dma_mapping_error(dma_address)) {
- /* restore sg */
- sg->length += qc->pad_len;
- return -1;
- }
-
- sg_dma_address(sg) = dma_address;
- sg_dma_len(sg) = sg->length;
-
-skip_map:
- DPRINTK("mapped buffer of %d bytes for %s\n", sg_dma_len(sg),
- qc->tf.flags & ATA_TFLAG_WRITE ? "write" : "read");
-
- return 0;
+
+ qc->nbytes = 0;
+ while (n_elem) {
+ qc->nbytes += sg->length;
+ n_elem--;
+ sg = sg_next(sg);
+ }
}

/**
@@ -6028,9 +5938,6 @@ void ata_qc_issue(struct ata_queued_cmd
if (ata_should_dma_map(qc)) {
if (qc->flags & ATA_QCFLAG_SG) {
if (ata_sg_setup(qc))
- goto sg_err;
- } else if (qc->flags & ATA_QCFLAG_SINGLE) {
- if (ata_sg_setup_one(qc))
goto sg_err;
}
} else {
diff -r 8b1075c7ad47 include/linux/libata.h
--- a/include/linux/libata.h Tue Nov 13 21:00:47 2007 +1100
+++ b/include/linux/libata.h Wed Nov 14 15:31:07 2007 +1100
@@ -216,8 +216,7 @@ enum {
/* struct ata_queued_cmd flags */
ATA_QCFLAG_ACTIVE = (1 << 0), /* cmd not yet ack'd to scsi lyer */
ATA_QCFLAG_SG = (1 << 1), /* have s/g table? */
- ATA_QCFLAG_SINGLE = (1 << 2), /* no s/g, just a single buffer */
- ATA_QCFLAG_DMAMAP = ATA_QCFLAG_SG | ATA_QCFLAG_SINGLE,
+ ATA_QCFLAG_DMAMAP = ATA_QCFLAG_SG,
ATA_QCFLAG_IO = (1 << 3), /* standard IO command */
ATA_QCFLAG_RESULT_TF = (1 << 4), /* result TF requested */
ATA_QCFLAG_CLEAR_EXCL = (1 << 5), /* clear excl_link on completion */
@@ -459,7 +458,6 @@ struct ata_queued_cmd {

struct scatterlist sgent;
struct scatterlist pad_sgent;
- void *buf_virt;

/* DO NOT iterate over __sg manually, use ata_for_each_sg() */
struct scatterlist *__sg;
-
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