Re: [PATCH] sata_sil: add Large Block Transfer support

[Robert Hancock]

Tejun Heo wrote:
> Hello,
>
> Robert Hancock wrote:
> > Obviously not 2.6.28 material, but could potentially head into .29.
> > I've done some testing with a DVD drive connected to this controller
> > and verified that reading off an entire DVD returns correct data
> > (and that the controller is actually getting requests that cross
> > 64K boundaries). More testing would certainly be useful..
>
> Ah... nice.  It would be great to have this in -next for some time.
>
> > +static void sil_bmdma_stop(struct ata_queued_cmd *qc)
> > +{
> > +    struct ata_port *ap = qc->ap;
> > +    void __iomem *mmio_base = ap->host->iomap[SIL_MMIO_BAR];
> > +    void __iomem *bmdma2 = mmio_base + sil_port[ap->port_no].bmdma2;
> > +
> > +    /* clear start/stop bit - can safely always write 0 */
> > +    writeb(0, bmdma2);
>
> ioread/iowrite?

We know the register's always MMIO on this controller, so it's slightly 
more optimal to avoid the conditional in there.

> > +    /* one-PIO-cycle guaranteed wait, per spec, for HDMA1:0 transition */
> > +    ata_sff_dma_pause(ap);
> > +}
> > +
> > +static void sil_bmdma_setup(struct ata_queued_cmd *qc)
> > +{
> > +    struct ata_port *ap = qc->ap;
> > +    void __iomem *bmdma = ap->ioaddr.bmdma_addr;
> > +
> > +    /* load PRD table addr. */
> > +    mb();    /* make sure PRD table writes are visible to controller */
>
> I know it's not specific to this change but does mb() really make
> sense here?  I don't think we need any barrier here.

Not sure. Documentation/memory-barriers.txt seems rather unfortunately 
vague on whether MMIO writes are strongly ordered with respect to memory 
writes. I seem to recall some debate on this a while ago, did it ever 
get resolved?

> > +    writel(ap->prd_dma, bmdma + ATA_DMA_TABLE_OFS);
> > +
> > +    /* issue r/w command */
> > +    ap->ops->sff_exec_command(ap, &qc->tf);
> > +}
>
> Thanks.
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