linux-kernel - Re: [PATCH] libata: Cable detection fixes

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Date:	Thu, 01 Mar 2007 20:26:56 -0500
From:	Jeff Garzik <jeff@...zik.org>
To:	Alan <alan@...rguk.ukuu.org.uk>
CC:	linux-ide@...r.kernel.org, linux-kernel@...r.kernel.org,
	Andrew Morton <akpm@...ux-foundation.org>, torvalds@...l.org
Subject: Re: [PATCH] libata: Cable detection fixes

Alan wrote:
> 2.6.21-rc has horrible problems with libata and PATA cable types (and
> thus speeds). This occurs because Tejun fixed a pile of other bugs and
> we now do cable detect enforcement for drive side detection properly.
> 
> Unfortunately we don't do the process around cable detection right. Tejun
> identified the problem and pointed to the right Annex in the spec, this patch
> implements the needed changes.
> 
> The basic requirement is that we have to identify the slave before the
> master.
> 
> The patch switches the identify order so that we can do the drive side
> detection correctly. 
> 
> Secondly we add a ->cable_detect() method called after the identify
> sequence which allows a host to do host side detection at this point
> should it wish, or to modify the results of the drive side identify.
[...]

> @@ -1850,8 +1900,11 @@
>  	for (i = 0; i < ATA_MAX_DEVICES; i++)
>  		ap->device[i].pio_mode = XFER_PIO_0;
>  
> -	/* read IDENTIFY page and configure devices */
> -	for (i = 0; i < ATA_MAX_DEVICES; i++) {
> +	/* read IDENTIFY page and configure devices. We have to do the identify
> +	   specific sequence bass-ackwards so that PDIAG- is released by
> +	   the slave device */
> +
> +	for (i = ATA_MAX_DEVICES - 1; i >=  0; i--) {
>  		dev = &ap->device[i];
>  
>  		if (tries[i])
> @@ -1864,6 +1917,19 @@
>  				     dev->id);
>  		if (rc)
>  			goto fail;
> +	}
> +
> +	/* Now ask for the cable type as PDIAG- should have been released */
> +	if (ap->ops->cable_detect)
> +		ap->cbl = ap->ops->cable_detect(ap);
> +
> +	/* After the identify sequence we can now set up the devices. We do
> +	   this in the normal order so that the user doesn't get confused */
> +
> +	for(i = 0; i < ATA_MAX_DEVICES; i++) {
> +		dev = &ap->device[i];
> +		if (!ata_dev_enabled(dev))
> +			continue;
>  
>  		ap->eh_context.i.flags |= ATA_EHI_PRINTINFO;
>  		rc = ata_dev_configure(dev);


ACK pending positive testing reports

However, given that we are in -rc cycle, and the wide impact of this 
change, this patch wants splitting.  The ->cable_detect stuff should be 
in a separate patch from the IDENTIFY DEVICE ordering stuff.  This 
ensures sanity when git-bisecting changes, and allows fast-tracking of 
the identify-ordering change.

At present, adding the new ->cable_detect hook looks like 2.6.22 
material (#upstream) rather than 2.6.21-rc (#upstream-fixes).

	Jeff


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