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    SubjectRe: Serial 8250 DMA Broken on OMAP3630
    On Wed, Oct 9, 2019 at 8:42 AM Vignesh Raghavendra <vigneshr@ti.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.

    adam
    >
    > > adam
    > >
    >
    > --
    > Regards
    > Vignesh

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