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Date: Mon, 09 Feb 2015 22:26:42 +0100
From: Hans Petter Selasky <hps@selasky.org>
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To: gljennjohn@gmail.com, usb@freebsd.org, John Baldwin <jhb@freebsd.org>
Subject: Re: r276717 causes problems
References: <20150209183648.7825eee5@ernst.home>
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Hi John,

Do all PCI busses support 64-bit DMA busmaster? Do we reflect this in 
the busdma tags passed down to device drivers?

--HPS

On 02/09/15 18:36, Gary Jennejohn wrote:
> r276717 breaks access to my 4-disk external USB3 (XHCI) enclosure.
>
> The symptom is that only the first of the threee disks is found.
>
> r276716 sees all the disks immediately.
>
> This is the output for the bridge chip:
>
> umass0: <JMicron USB to ATAATAPI Bridge, class 0/0, rev 3.00/28.03, addr 2> on usbus0
>
> The problem seems to be mainly due to setting dma_bits to 64.  It's
> true that the chip on the controller board supports 64 bit DMA, but the
> JMicron seems to have a real crisis when that setting is used, although
> I don't know why.
>
> Note that the nice output above was obtained after hard coding dma_bits
> to 32 in xhci_init().  With 64 bits I see this:
>
> umass0: <vendor 0x152d product 0x0539, class 0/0, rev 3.00/28.03, addr 3> on usbus0
>
> probably because reading the strings from the device fails.
>
> Anyway, it would be nice to have a sysctl to force dma_bits to 32.
>
> Unfortunately, I still have a problem with my enclosure with more
> current versions of HEAD.  The rather questionable practice of
> always doing a multi LUN enquiry using the SCSI-3 CDB byte 0xa0
> also causes problems.  Considering that most of these bridge
> chips can barely emulate SCSI-2 it seems rather foolish to try to
> jam SCSI-3 CDB bytes down their throats.
>
> But that's a different story.
>