From: Alan Stern <stern@rowland.harvard.edu>
To: Stanislaw Gruszka <sgruszka@redhat.com>
Cc: Stefan Wahren <stefan.wahren@i2se.com>,
Lorenzo Bianconi <lorenzo.bianconi@redhat.com>,
Felix Fietkau <nbd@nbd.name>,
Doug Anderson <dianders@chromium.org>,
Minas Harutyunyan <hminas@synopsys.com>,
USB list <linux-usb@vger.kernel.org>,
linux-wireless <linux-wireless@vger.kernel.org>
Subject: Re: [BUG] mt76x0u: Probing issues on Raspberry Pi 3 B+
Date: Wed, 20 Feb 2019 10:25:14 -0500 (EST) [thread overview]
Message-ID: <Pine.LNX.4.44L0.1902201023060.1589-100000@iolanthe.rowland.org> (raw)
In-Reply-To: <20190220102050.GA7195@redhat.com>
On Wed, 20 Feb 2019, Stanislaw Gruszka wrote:
> On Tue, Feb 19, 2019 at 10:40:47AM -0500, Alan Stern wrote:
> > On Tue, 19 Feb 2019, Stanislaw Gruszka wrote:
> >
> > > It would be interesting why urb->num_sgs = 0 & urb->sg cause
> > > the troubles. This is how usb_sg_init() submit urbs for sg_tablesize = 0
> > > controllers. So either are there are some requirement on urb->sg
> > > mapped via dma_map_page() (which mt76usb does not meet) not needed
> > > for urb->transfer_buffer mapped via dma_map_single() or there
> > > is something wrong in dwc2 with sg and this driver will not
> > > work with urb_sg_init() as well. I don't have hardware to investigate
> > > this and don't want to bother you with more patches.
> >
> > urb->sg != NULL and urb->num_sgs == 0 means that the transfer buffer
> > must fit into a single page, which is pointed to by the first element
> > of the scatterlist.
>
> I asked about that in other thread
> https://lore.kernel.org/linux-wireless/2cc5674a-a3a0-d8fe-65f5-4357da9b85d3@arm.com/
>
> the answer was it is weird but valid. However I think do dma_map_page()
> on buffer not fit in the single page is asking for troubles. I just posted
> patch that should fix this for mt76usb.
>
> > But now that I look at the code in usb_sg_init(), it seems odd that the
> > !use_sg case doesn't increment sg during each loop iteration. I don't
> > see how that could possibly work -- it looks like a bug!
>
> Looks for me that this is done via for_each_sg(sg, sg, io->entries, i) loop.
Ah, of course. Thanks for straightening me out; it's surprising what
blind spots one's brain can develop.
Alan Stern
next prev parent reply other threads:[~2019-02-20 15:25 UTC|newest]
Thread overview: 59+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20190211173315.GE6292@redhat.com>
[not found] ` <Pine.LNX.4.44L0.1902111246410.1543-100000@iolanthe.rowland.org>
2019-02-12 0:06 ` [BUG] mt76x0u: Probing issues on Raspberry Pi 3 B+ Lorenzo Bianconi
2019-02-12 9:30 ` Stanislaw Gruszka
2019-02-12 11:58 ` Lorenzo Bianconi
2019-02-12 13:15 ` Stanislaw Gruszka
2019-02-14 6:49 ` Stefan Wahren
2019-02-14 9:25 ` Stanislaw Gruszka
2019-02-14 9:48 ` Stefan Wahren
2019-02-14 9:54 ` Stanislaw Gruszka
2019-02-15 7:12 ` Stanislaw Gruszka
2019-02-16 11:05 ` Stefan Wahren
2019-02-16 14:07 ` Stanislaw Gruszka
2019-02-16 19:17 ` Stefan Wahren
2019-02-18 13:52 ` Stanislaw Gruszka
2019-02-18 14:25 ` Lorenzo Bianconi
2019-02-18 14:47 ` Stanislaw Gruszka
2019-02-18 14:43 ` Felix Fietkau
2019-02-18 15:03 ` Stanislaw Gruszka
2019-02-18 18:52 ` Felix Fietkau
2019-02-19 10:42 ` Stanislaw Gruszka
2019-02-19 12:19 ` Felix Fietkau
2019-02-20 13:00 ` Stanislaw Gruszka
2019-02-20 13:22 ` Lorenzo Bianconi
2019-02-20 16:14 ` Stanislaw Gruszka
2019-02-20 16:22 ` Lorenzo Bianconi
2019-02-20 16:32 ` Stanislaw Gruszka
2019-02-20 16:36 ` Lorenzo Bianconi
2019-03-03 21:16 ` Stefan Wahren
2019-02-18 22:19 ` Stefan Wahren
2019-02-19 10:59 ` Stanislaw Gruszka
2019-02-19 12:11 ` Felix Fietkau
2019-02-19 15:40 ` Alan Stern
2019-02-20 10:20 ` Stanislaw Gruszka
2019-02-20 15:25 ` Alan Stern [this message]
2019-02-19 17:02 ` Stefan Wahren
2019-02-12 15:27 ` Alan Stern
2019-02-09 12:08 Stefan Wahren
2019-02-09 18:46 ` Lorenzo Bianconi
2019-02-09 20:29 ` Stefan Wahren
2019-02-09 20:33 ` Lorenzo Bianconi
2019-02-09 22:47 ` Stefan Wahren
2019-02-10 9:41 ` Stanislaw Gruszka
2019-02-10 10:22 ` Lorenzo Bianconi
2019-02-11 7:44 ` Stanislaw Gruszka
2019-02-11 10:04 ` Lorenzo Bianconi
2019-02-11 10:33 ` Stefan Wahren
2019-02-11 11:06 ` Lorenzo Bianconi
2019-02-11 14:04 ` Stefan Wahren
2019-02-11 15:10 ` Lorenzo Bianconi
2019-02-11 15:27 ` Stefan Wahren
2019-02-11 15:57 ` Lorenzo Bianconi
2019-02-13 7:05 ` Stefan Wahren
2019-02-11 17:22 ` Stanislaw Gruszka
2019-02-10 9:29 ` Stanislaw Gruszka
2019-02-10 16:38 ` Stefan Wahren
2019-02-10 16:52 ` Lorenzo Bianconi
2019-02-10 17:39 ` Lorenzo Bianconi
2019-02-11 7:50 ` Stanislaw Gruszka
2019-02-11 8:08 ` Stefan Wahren
2019-02-11 9:52 ` Lorenzo Bianconi
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