Re: SATA_SIL on IXP425 workaround

[Jeff Garzik <jeff@garzik.org>]

On 01/21/2010 01:48 AM, Jeff Garzik wrote:
> 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.

It is definitely possible to do all 32-bit accesses...  but that 
requires activating and exclusively using the command buffering feature, 
because direct 32-bit access to the taskfile registers will result in a 
32-bit access to Data rather than the desired effect.

The chip docs are at http://gkernel.sourceforge.net/specs/sii/ for those 
unfamiliar with my doc archive.

	Jeff