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From: Alan Stern <stern@rowland.harvard.edu>
To: Christoph Hellwig <hch@lst.de>
Cc: Oliver Neukum <oneukum@suse.com>,
	"iommu@lists.linux-foundation.org"
	<iommu@lists.linux-foundation.org>,
	Yoshihiro Shimoda <yoshihiro.shimoda.uh@renesas.com>,
	"linux-block@vger.kernel.org" <linux-block@vger.kernel.org>,
	Linux-Renesas <linux-renesas-soc@vger.kernel.org>,
	"linux-usb@vger.kernel.org" <linux-usb@vger.kernel.org>
Subject: Re: How to resolve an issue in swiotlb environment?
Date: Wed, 12 Jun 2019 10:43:11 -0400 (EDT)	[thread overview]
Message-ID: <Pine.LNX.4.44L0.1906121038210.1557-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <20190612120653.GA25285@lst.de>

On Wed, 12 Jun 2019, Christoph Hellwig wrote:

> On Wed, Jun 12, 2019 at 01:46:06PM +0200, Oliver Neukum wrote:
> > > Thay is someething the virt_boundary prevents.  But could still give
> > > you something like:
> > > 
> > > 	1536 4096 4096 1024
> > > 
> > > or
> > > 	1536 16384 8192 4096 16384 512
> > 
> > That would kill the driver, if maxpacket were 1024.
> > 
> > USB has really two kinds of requirements
> > 
> > 1. What comes from the protocol
> > 2. What comes from the HCD
> > 
> > The protocol wants just multiples of maxpacket. XHCI can satisfy
> > that in arbitrary scatter/gather. Other HCs cannot.
> 
> We have no real way to enforce that for the other HCs unfortunately.
> I can't really think of any better way to handle their limitations
> except for setting max_segments to 1 or bounce buffering.

Would it be okay to rely on the assumption that USB block devices never 
have block size < 512?  (We could even add code to the driver to 
enforce this, although refusing to handle such devices at all might be 
worse than getting an occasional error.)

As I mentioned before, the only HCD that sometimes ends up with
maxpacket = 1024 but is unable to do full SG is vhci-hcd, and that one
shouldn't be too hard to fix.

Alan Stern


  reply	other threads:[~2019-06-12 14:44 UTC|newest]

Thread overview: 26+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-06-03  6:42 How to resolve an issue in swiotlb environment? Yoshihiro Shimoda
2019-06-07 12:00 ` Yoshihiro Shimoda
2019-06-10  7:31   ` Biju Das
2019-06-10 11:13   ` Yoshihiro Shimoda
2019-06-10 12:32     ` Christoph Hellwig
2019-06-10 18:46       ` Alan Stern
2019-06-11  6:41         ` Christoph Hellwig
2019-06-11 14:51           ` Alan Stern
2019-06-12  7:30             ` Christoph Hellwig
2019-06-12  8:52               ` Yoshihiro Shimoda
2019-06-12 11:31                 ` Christoph Hellwig
2019-06-13  4:52                   ` Yoshihiro Shimoda
2019-06-12 11:46               ` Oliver Neukum
2019-06-12 12:06                 ` Christoph Hellwig
2019-06-12 14:43                   ` Alan Stern [this message]
2019-06-13  7:39                     ` Christoph Hellwig
2019-06-13 16:57                       ` Martin K. Petersen
2019-06-13 17:16                       ` Alan Stern
2019-06-13 18:18                         ` Greg KH
2019-06-13 23:01                         ` shuah
2019-06-14 14:44                           ` Alan Stern
2019-06-18 15:28                             ` shuah
2019-06-19 20:23                               ` shuah
2019-06-19 21:05                                 ` Alan Stern
2019-06-21 17:43                                   ` Suwan Kim
2019-06-11  6:49         ` Yoshihiro Shimoda

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