linux-kernel - Re: [PATCH] sata_sil: add Large Block Transfer support

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Date:	Mon, 22 Dec 2008 22:35:59 -0600
From:	Robert Hancock <hancockr@...w.ca>
To:	Tejun Heo <tj@...nel.org>
CC:	ide <linux-ide@...r.kernel.org>,
	linux-kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] sata_sil: add Large Block Transfer support

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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