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Date: Thu, 27 Feb 2020 16:34:33 -0600 From: Rob Herring <robh+dt@...nel.org> To: Michael Walle <michael@...le.cc> Cc: "open list:SERIAL DRIVERS" <linux-serial@...r.kernel.org>, devicetree@...r.kernel.org, "linux-kernel@...r.kernel.org" <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>, Li Yang <leoyang.li@....com>, 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 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. Rob
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