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ahci: unify sglist preparation 

The intent of this patch is to further unify the creation and
deletion of the sglist used for all AHCI transfers, including
emulated PIO, ATAPI R/W, and native DMA R/W.

By replacing ahci_start_transfer's call to ahci_populate_sglist
with ahci_dma_prepare_buf, we reduce the number of direct calls
where we manipulate the scatter-gather list in the AHCI code.

To make this switch, the constant "0" passed as an offset
in ahci_dma_prepare_buf is adjusted to use io_buffer_offset.

For DMA pathways, this has no effect: io_buffer_offset is always
updated to 0 at the beginning of a DMA transfer loop regardless.
DMA pathways through ide_dma_cb() update the io_buffer_offset
accordingly, and for circumstances where we might make several
trips through this loop, this may actually correct a design flaw.

For PIO pathways, the newly updated ahci_dma_prepare_buf will
now prepare the sglist at the correct offset. It will also set
io_buffer_size, but this is not used in the cmd_read_pio or
cmd_write_pio pathways.

Signed-off-by: John Snow <jsnow@redhat.com>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Message-id: 1414785819-26209-3-git-send-email-jsnow@redhat.com
Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
This commit is contained in:
John Snow 2014-10-31 16:03:38 -04:00 committed by Stefan Hajnoczi
parent 36334faf35
commit bef1301acb
1 changed files with 2 additions and 2 deletions
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4
hw/ide/ahci.c
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@ -1093,7 +1093,7 @@ static void ahci_start_transfer(IDEDMA *dma)
goto out;
}
if (!ahci_populate_sglist(ad, &s->sg, s->io_buffer_offset)) {
if (ahci_dma_prepare_buf(dma, is_write)) {
has_sglist = 1;
}
@ -1145,7 +1145,7 @@ static int ahci_dma_prepare_buf(IDEDMA *dma, int is_write)
AHCIDevice *ad = DO_UPCAST(AHCIDevice, dma, dma);
IDEState *s = &ad->port.ifs[0];
ahci_populate_sglist(ad, &s->sg, 0);
ahci_populate_sglist(ad, &s->sg, s->io_buffer_offset);
s->io_buffer_size = s->sg.size;
DPRINTF(ad->port_no, "len=%#x\n", s->io_buffer_size);