linux-kernel - Re: Serial 8250 DMA Broken on OMAP3630

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Message-ID: <CAHCN7xJYJ7f3b9D+tMw=f4zda8H=NyNV4UdeT+65MJxrcu3bkg@mail.gmail.com>
Date:   Wed, 9 Oct 2019 14:27:18 -0500
From:   Adam Ford <aford173@...il.com>
To:     Tony Lindgren <tony@...mide.com>
Cc:     Vignesh Raghavendra <vigneshr@...com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Jiri Slaby <jslaby@...e.com>,
        Andy Shevchenko <andriy.shevchenko@...ux.intel.com>,
        Douglas Anderson <dianders@...omium.org>,
        Yegor Yefremov <yegorslists@...glemail.com>,
        linux-serial@...r.kernel.org,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: Serial 8250 DMA Broken on OMAP3630

On Wed, Oct 9, 2019 at 12:34 PM Tony Lindgren <tony@...mide.com> wrote:
>
> * Adam Ford <aford173@...il.com> [191009 14:09]:
> > On Wed, Oct 9, 2019 at 8:42 AM Vignesh Raghavendra <vigneshr@...com> wrote:
> > >
> > > Hi Adam,
> > >
> > > On 06/10/19 10:34 PM, Adam Ford wrote:
> > > > Has anyone else had any issues using the CONFIG_SERIAL_8250_DMA on the OMAP?
> > > >
> > > > I can use the DMA on the legacy, omap-serial driver, but when I enable
> > > > the DMA on the 8250-omap driver, I get missing frames in Bluetooth.
> > > >
> > > > The older driver seems to have an ISR that seems to address a variety
> > > > of items compared to the very tiny ISR for 8250-omap.c.
> > > >
> > > > I am not exactly sure where to start, but if someone has any
> > > > suggestions on how I can troubleshoot, please let me know.  As of now,
> > > > I have to disable CONFIG_SERIAL_8250_DMA to get the Bluetooth
> > > > connected to UART2 operational on a DM3730 at 3,000,000 baud, but it
> > > > appears to work just fine after some patches I just submitted for
> > > > handling RTS/CTS.  The legacy omap-serial driver works fine with DMA.
> > > >
> > >
> > > Mainline omap-serial does not support DMA (evident from lack of
> > > dmaengine API calls) and therefore is not a regression. So OMAP3 UART
> > > DMA was never tested at least with 8250 driver.
> > > I am not sure enabling UART DMA on OMAP3 would be a trivial job. We need
> > > analyse of whether all erratas workarounds are implemented and see if
> > > there any difference wrt DMA integration itself. Do we know if UART DMA
> > > ever worked on OMAP3 previously?
> >
> > Can we disable CONFIG_SERIAL_8250_DMA from omap2plus_defconfig?   As
> > of right now, it's the only way I can use the Bluetooth.  There are
> > #ifdef's in the 8250-omap driver, so it looks like some of the hooks
> > are there, but if it's incomplete, it seems like we shouldn't enable
> > this config option by default yet.
>
> From what I recall I tested that DMA on omap3 worked fine with runtime
> PM for console. Certainly there are issues still remaining though.
>
> If you want to disable dma for a specific port, just delete the
> add /delete-property/dma-names for the port in question in your
> board specific dts file.
>
> See 8250_omap.c for of_property_count_strings(np, "dma-names").

Thank you.  That seems to have worked.  I'll check the AM3517 when I
have some time to see if it needs the same patch.  For now, I pushed
the patch to the omap mailing list for the Logic PD Torpedo board.

Should we consider removing the OMAP_SERIAL from omap2plus_defconfig
in the 8250 is the preferred driver?  It seems odd to me that both
drivers are enabled.

adam
>
> Regards,
>
> Tony
>
>