linux-kernel - Re: SATA_SIL on IXP425 workaround

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Message-ID: <4B57F8D6.6080902@garzik.org>
Date:	Thu, 21 Jan 2010 01:48:54 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	Bartlomiej Zolnierkiewicz <bzolnier@...il.com>,
	Krzysztof Halasa <khc@...waw.pl>
CC:	linux-ide@...r.kernel.org, lkml <linux-kernel@...r.kernel.org>
Subject: Re: 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.

	Jeff



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