linux-kernel - Re: [PATCH v2 3/9] tty: serial: fsl_lpuart: handle EPROBE

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Date:   Fri, 28 Feb 2020 15:53:47 -0600
From:   Li Yang <leoyang.li@....com>
To:     Michael Walle <michael@...le.cc>
Cc:     Rob Herring <robh+dt@...nel.org>,
        "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>,
        "open list:OPEN FIRMWARE AND FLATTENED DEVICE TREE BINDINGS" 
        <devicetree@...r.kernel.org>, lkml <linux-kernel@...r.kernel.org>,
        "moderated list:ARM/FREESCALE IMX / MXC ARM ARCHITECTURE" 
        <linux-arm-kernel@...ts.infradead.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Mark Rutland <mark.rutland@....com>,
        Shawn Guo <shawnguo@...nel.org>, Jiri Slaby <jslaby@...e.com>,
        Peng Fan <peng.fan@....com>,
        Vabhav Sharma <vabhav.sharma@....com>
Subject: Re: [PATCH v2 3/9] tty: serial: fsl_lpuart: handle EPROBE_DEFER for DMA

On Fri, Feb 28, 2020 at 3:51 PM Michael Walle <michael@...le.cc> wrote:
>
> Am 2020-02-28 12:46, schrieb Michael Walle:
> > Hi Rob, Hi Leo,
> >
> > Am 2020-02-28 00:03, schrieb Rob Herring:
> >> On Thu, Feb 27, 2020 at 4:49 PM Li Yang <leoyang.li@....com> wrote:
> >>>
> >>> On Thu, Feb 27, 2020 at 4:35 PM Rob Herring <robh+dt@...nel.org>
> >>> wrote:
> >>> >
> >>> > On Fri, Feb 21, 2020 at 11:48 AM Michael Walle <michael@...le.cc> wrote:
> >>> > >
> >>> > > The DMA channel might not be available at the first probe time. This is
> >>> > > esp. the case if the DMA controller has an IOMMU mapping.
> >>> > >
> >>> > > Use the new dma_request_chan() API and handle EPROBE_DEFER errors. Also
> >>> > > reorder the code a bit, so that we don't prepare the whole UART just to
> >>> > > determine that the DMA channel is not ready yet and we have to undo all
> >>> > > the stuff. Try to map the DMA channels earlier.
> >>> >
> >>> > Changing this means you never probe successfully if you boot a kernel
> >>> > with the DMA driver disabled (or it's IOMMU disabled). Some other
> >>> > drivers request DMA in open() and can work either way.
> >
> > Oh, I see.
> >
> >>> We got this exact issue previously with another driver.  When the
> >
> > What driver is it? I've been working on the i2c-mxs.c driver which has
>
> whoops, i2c-imx.c, not i2c-mxs.c

Ya.  Same one.  I have added CONFIG_FSL_EDMA into the arm64/defconfig
as a workaround.

Regards,
Leo