linux-kernel - Re: [PATCH] libata: Add MMIO support to pata

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Date:	Mon, 25 Feb 2008 17:57:07 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	Tim Ellis <tim@...dg.com>
CC:	benh@...nel.crashing.org,
	Guennadi Liakhovetski <g.liakhovetski@....de>,
	Alan Cox <alan@...rguk.ukuu.org.uk>,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH] libata: Add MMIO support to pata_sil680

Tim Ellis wrote:
> 
> On 15 Feb 2008, at 21:45, Benjamin Herrenschmidt wrote:
> 
>>
>> On Fri, 2008-02-15 at 15:53 +0000, Alan Cox wrote:
>>>>> That's strange though. Somebody with knowledge of that HW (or 
>>>>> specs) who
>>>>> can spot something ? Could it be an issue with timing ?
>>>>>
>>>>> I don't have HW access to this machine. If somebody could send one 
>>>>> to me
>>>>> I could do more investigation.
>>>>
>>>> Ben, would an ssh access to such a machine and to a terminal server
>>>> suffice?
>>>
>>> It says clearly in the code where to start. See the FIXME notes in both
>>> libata-sff and libata-core about MMIO. Neither the DMA transfer start or
>>> the probe SRST sequence are correct with MMIO posting and this hasn't
>>> been fixed as I pointed out was needed when I originally NAKked the
>>> change.
>>>
>>> Without those being fixed (especially SRST) on any device with heavy PCI
>>> posting of mmio your controller *wont work*.
>>
>> The dbdma start is mostly harmless (things don't get posted for -that-
>> long), though I suppose it's worth fixing. Would reading back dmactl do
>> in that case or do you foresee any kind of side effect ? (Maybe only
>> doing it for MMIO ?)
>>
>> As for SRST, I'm not totally confident how safe it is to read back
>> there while doing the reset sequence, so I'm tempted to really only
>> do it for MMIO and use altstat rather than ctl/stat (the later tends
>> to have side effects which we don't want here).
>>
>> What do you think ?
>>
>> The main problem from here is that I don't know whether we are using
>> MMIO or PIO from libata-core. Maybe I can add a host flag indicate
>> that such flushing is needed ?
>>
>> In the meantime, Guennadi, can you check if that patch helps for you
>> (to see if that is indeed the problem):
>>
>>
>> diff --git a/drivers/ata/libata-core.c b/drivers/ata/libata-core.c
>> index 004dae4..1451a52 100644
>> --- a/drivers/ata/libata-core.c
>> +++ b/drivers/ata/libata-core.c
>> @@ -3461,10 +3461,13 @@ static int ata_bus_softreset(struct ata_port 
>> *ap, unsigned int devmask,
>>
>>     /* software reset.  causes dev0 to be selected */
>>     iowrite8(ap->ctl, ioaddr->ctl_addr);
>> +    ioread16(ioaddr->nsect_addr);
>>     udelay(20);    /* FIXME: flush */
>>     iowrite8(ap->ctl | ATA_SRST, ioaddr->ctl_addr);
>> +    ioread16(ioaddr->nsect_addr);
>>     udelay(20);    /* FIXME: flush */
>>     iowrite8(ap->ctl, ioaddr->ctl_addr);
>> +    ioread16(ioaddr->nsect_addr);
>>
>>     /* wait a while before checking status */
>>     ata_wait_after_reset(ap, deadline);
>> diff --git a/drivers/ata/libata-sff.c b/drivers/ata/libata-sff.c
>> index 60cd4b1..81d5828 100644
>> --- a/drivers/ata/libata-sff.c
>> +++ b/drivers/ata/libata-sff.c
>> @@ -273,6 +273,7 @@ void ata_bmdma_start(struct ata_queued_cmd *qc)
>>      * FIXME: The posting of this write means I/O starts are
>>      * unneccessarily delayed for MMIO
>>      */
>> +    ioread8(ap->ioaddr.bmdma_addr + ATA_DMA_CMD);
>> }
>>
>> /**
>>
>> Cheers,
>> Ben.
> 
> 
> Unfortunately this patch appears to give same result as in the original 
> post. Guennadi and I are looking into arranging access to a device. Thanks!

Yes.

Alan loves to complain about lack of MMIO flush, but in practice this is 
rarely the source of problems such as the one you describe.

But if its broken its broken, and we need to revert.  Any luck getting 
benh access to the device?

	Jeff



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