From: James Bottomley <James.Bottomley@HansenPartnership.com>
To: Tom Yan <tom.ty89@gmail.com>
Cc: Greg KH <gregkh@linuxfoundation.org>,
Gerd Hoffmann <kraxel@redhat.com>,
Alan Stern <stern@rowland.harvard.edu>,
linux-usb@vger.kernel.org, linux-scsi@vger.kernel.org,
stable@vger.kernel.org, hdegoede@redhat.com
Subject: Re: [PATCH 1/1] uas: leave can_queue as MAX_CMNDS if device reports larger qdepth
Date: Mon, 23 May 2016 12:07:47 -0700 [thread overview]
Message-ID: <1464030467.2331.41.camel@HansenPartnership.com> (raw)
In-Reply-To: <CAGnHSEn=5CvtKGXyxpyDRtV1Wu9d8Z0fo26p=8-YYvBDmMf8fw@mail.gmail.com>
On Tue, 2016-05-24 at 02:33 +0800, Tom Yan wrote:
> I don't quite get what you mean. Are you saying that it is impossible
> that UAS devices would report inappropriately high qdepth, because of
> this?
> https://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/
> drivers/usb/storage/uas.c?h=v4.6#n908
OK, you found the statement, now translate what it means to resource
allocation and it will show you why the if you proposed to add would
always be true.
James
> In that case should I send another patch that simply has `.can_queue
> =
> MAX_CMNDS` in the host template removed?
>
> On 24 May 2016 at 01:27, James Bottomley
> <James.Bottomley@hansenpartnership.com> wrote:
> > On Tue, 2016-05-24 at 01:23 +0800, Tom Yan wrote:
> > > Nothing wrong. It's just .can_queue = MAX_CMNDS in the host
> > > template
> > > is no longer neceesary, since with his patch, uas will set
> > > can_queue
> > > again later (to devinfo->qdepth - 2).
> > >
> > > Originally I thought .can_queue = MAX_CMNDS can hence be removed;
> > > but
> > > after a second thought, I think it might probably be better if we
> > > leave it there and make use of it, in case certain device somehow
> > > inapproriately reports an enormous qdepth (i.e. larger than
> > > MAX_CMNDS). (According to the commit message of 55ff8cfbc4e1
> > > ("USB:
> > > uas: Reduce can_queue to MAX_CMNDS"), "The uas driver can never
> > > queue
> > > more then MAX_CMNDS...")
> >
> > OK, so try this as an exercise: Why would this not be the right
> > thing
> > to do after the host is prepared: It has to do with the streams
> > resources the driver has already created.
> >
> > James
> >
> >
> --
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>
prev parent reply other threads:[~2016-05-23 19:07 UTC|newest]
Thread overview: 6+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-23 16:02 [PATCH 1/1] uas: leave can_queue as MAX_CMNDS if device reports larger qdepth tom.ty89
2016-05-23 17:00 ` Greg KH
2016-05-23 17:23 ` Tom Yan
2016-05-23 17:27 ` James Bottomley
2016-05-23 18:33 ` Tom Yan
2016-05-23 19:07 ` James Bottomley [this message]
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