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    SubjectRe: SATA_SIL on IXP425 workaround
    On 01/20/2010 11:58 PM, Jeff Garzik wrote:
    > On 01/14/2010 10:59 AM, Bartlomiej Zolnierkiewicz wrote:
    >> On Monday 09 November 2009 06:31:21 pm Krzysztof Halasa wrote:
    >>> I'm trying to add a workaround for IXP4xx CPUs to SATA SIL driver. The
    >>> problem is that IXP4xx CPUs (Intel's XScale (ARM) network-oriented
    >>> processors) are unable to perform 8 and 16-bit read from PCI MMIO, they
    >>> can only do a full 32-bit readl(); SIL chips respond to that with PCI
    >>> abort. The workaround is to use 8 and 16-bit regular IO reads (inb/inw)
    >>> instead (MMIO write is not a problem).
    >>> For SIL3x12 the workaround is simple (attached) and it works on my 3512.
    >>> I'm not sure about 3114 (the 4-port chip) - the PIO BARs have TF, CTL
    >>> and BWDMA registers which are common to channels 0 and 2, and (the other
    >>> set) to channels 1 and 3. Channel selection is done with bit 4 of
    >>> device/head TF register, this is similar (same?) as PATA master/slave.
    >>> Does that mean that I can simply treat channel 0 as PRI master, ch#2 as
    >>> PRI slave, ch#1 as SEC master and ch#3 as SEC slave, and the SFF code
    >>> will select the right device correctly? Does it need additional code?
    >>> I don't have anything based on 3114.
    >>> Note: the large PRD is not a problem here, the transfer can be started
    >>> by MMIO write. Only reads are an issue.
    >> FWIW your patch is now in my atang tree (I'm aware that Jeff is working
    >> on generic solution but in the meantime this non-intrusive patch allows
    >> sata_sil to work on IXP425).
    > I was asking an open question, is a generic solution possible?
    > Something like the attached patch might work, due it is completely
    > untested, and I did not verify that the BMDMA Status register is not
    > stomped. Also, the additional ioread32() calls in bmdma start/stop are
    > LIKELY to be unnecessary.

    As I suspected, there is a W1C register in there. But it does look
    possible to do all-32-bit accesses.


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