From: "Antti Seppälä" <a.seppala@gmail.com>
To: Guenter Roeck <linux@roeck-us.net>
Cc: Doug Anderson <dianders@chromium.org>,
Minas Harutyunyan <hminas@synopsys.com>,
Greg Kroah-Hartman <gregkh@linuxfoundation.org>,
Boris ARZUR <boris@konbu.org>,
linux-usb@vger.kernel.org, LKML <linux-kernel@vger.kernel.org>,
Felipe Balbi <balbi@kernel.org>,
Stefan Wahren <stefan.wahren@i2se.com>,
Martin Schiller <ms@dev.tdt.de>
Subject: Re: [RFT PATCH 1/4] usb: dwc2: Simplify and fix DMA alignment code
Date: Sun, 1 Mar 2020 18:51:55 +0200 [thread overview]
Message-ID: <CAKv9HNZjWKS1thKZ84FwYabHr-o2Q-T9xc4V2Oz6NtiuogQfRQ@mail.gmail.com> (raw)
In-Reply-To: <28e29bb7-b536-dd0f-d410-f4add6b2a9ab@roeck-us.net>
On Sun, 1 Mar 2020 at 18:24, Guenter Roeck <linux@roeck-us.net> wrote:
>
> Hi Antti,
>
> On 3/1/20 7:51 AM, Antti Seppälä wrote:
> > On Sat, 29 Feb 2020 at 18:33, Antti Seppälä <a.seppala@gmail.com> wrote:
> >>
> >> On Sat, 29 Feb 2020 at 17:25, Guenter Roeck <linux@roeck-us.net> wrote:
> >>>
> >>> Sigh. It would have been too simple. Too bad I can't test myself.
> >>> I'd like to know if this is because URB_NO_TRANSFER_DMA_MAP is set on a
> >>> transfer, or because the beginning of the buffer indeed needs to be aligned
> >>> to the DMA cache line size on that system. In the latter case, the question
> >>> is why the alignment to DWC2_USB_DMA_ALIGN (=4) works. In the former case,
> >>> question would be why the realignment does any good in the first place.
> >>>
> >>> Any chance you can add some test code to help figuring out what exactly
> >>> goes wrong ?
> >>>
> >>
> >> Sure, I can try to help. Just let me know what code you would like to
> >> insert and where and I'll see what I can do.
> >>
> >
> > So I did some further research on this and it turns out that:
> > - URB_NO_TRANSFER_DMA_MAP is not set on the offending transfers so
> > the issue really is buffer alignment
> > - DWC2_USB_DMA_ALIGN=4 "works" because in my limited testcase (usb
> > 4g-dongle utilized via qmi-wwan) all transfers are unaligned. That is,
> > every urb->transfer_buffer is misaligned by 2 bytes == unaligned
> > - I can fix both issues and thus make the patch work on MIPS by
> > modifying it like this:
> >
> > -#define DWC2_USB_DMA_ALIGN 4
> > +#define DWC2_USB_DMA_ALIGN dma_get_cache_alignment()
> >
> > struct dma_aligned_buffer {
> > void *old_xfer_buffer;
> > - u8 data[0];
> > + u8 data[0] ____cacheline_aligned;
> > };
> >
>
> Thanks for the additional testing. That means that the existing code
> is already broken, or am I missing something ?
>
Yes, I believe the existing code is broken if 4 byte aligned transfers
occur. I seem to have no easy way to prove that though as none of my
devices generate those.
> Updating DWC2_USB_DMA_ALIGN to dma_get_cache_alignment() was part
> of my initial fix, but then I abandoned it because I thought, well,
> the existing alignment works, so that can't be the problem.
>
> Anyway, using ____cacheline_aligned is an excellent idea. I'll make
> the changes suggested above for the next version of my series.
>
Great. In the meanwhile I'll continue testing and will report back if
I find anything new.
--
Antti
next prev parent reply other threads:[~2020-03-01 16:52 UTC|newest]
Thread overview: 28+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-02-26 21:04 [RFT PATCH 0/4] usb: dwc2: Fixes and improvements Guenter Roeck
2020-02-26 21:04 ` [RFT PATCH 1/4] usb: dwc2: Simplify and fix DMA alignment code Guenter Roeck
2020-02-27 22:06 ` Doug Anderson
2020-02-27 22:27 ` Guenter Roeck
2020-02-28 4:28 ` Guenter Roeck
2020-02-28 16:14 ` Doug Anderson
2020-02-28 17:59 ` Guenter Roeck
2020-02-29 7:46 ` Antti Seppälä
2020-02-29 15:25 ` Guenter Roeck
2020-02-29 16:33 ` Antti Seppälä
2020-03-01 15:51 ` Antti Seppälä
2020-03-01 16:24 ` Guenter Roeck
2020-03-01 16:51 ` Antti Seppälä [this message]
2020-03-01 17:13 ` Guenter Roeck
2020-02-28 16:26 ` Stefan Wahren
2020-02-26 21:04 ` [RFT PATCH 2/4] usb: dwc2: Do not update data length if it is 0 on inbound transfers Guenter Roeck
2020-02-27 22:06 ` Doug Anderson
2020-02-28 0:32 ` Guenter Roeck
2020-02-26 21:04 ` [RFT PATCH 3/4] usb: dwc2: Abort transaction after errors with unknown reason Guenter Roeck
2020-02-27 22:06 ` Doug Anderson
2020-02-28 0:36 ` Guenter Roeck
2020-02-26 21:04 ` [RFT PATCH 4/4] usb: dwc2: Make "trimming xfer length" a debug message Guenter Roeck
2020-02-27 22:07 ` Doug Anderson
2020-02-28 0:38 ` Guenter Roeck
2020-02-29 1:50 ` [RFT PATCH 0/4] usb: dwc2: Fixes and improvements Boris ARZUR
2021-01-12 19:40 ` Nicolas Saenz Julienne
2021-01-12 19:44 ` Nicolas Saenz Julienne
2021-01-13 4:48 ` Guenter Roeck
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