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Re: How to tell DMA controller in qemu to terminate transfer ?

From: Guenter Roeck
Subject: Re: How to tell DMA controller in qemu to terminate transfer ?
Date: Fri, 10 Jan 2020 10:02:51 -0800
User-agent: Mutt/1.9.4 (2018-02-28)

On Fri, Jan 10, 2020 at 10:36:20AM +0000, Peter Maydell wrote:
> On Wed, 8 Jan 2020 at 18:36, Guenter Roeck <address@hidden> wrote:
> >
> > Hi,
> >
> > I am trying to fix DMA support with Exynos4210. The original commit
> > 59520dc65e ("hw/arm/exynos4210: Add DMA support for the Exynos4210") doesn't
> > really work, primarily because it assigns wrong interrupt lines (no idea
> > how I thought I tested that).
> >
> > Problem I have right now is that the pl330 peripheral DMA in Exynos4210
> > depends on a signal from the peripheral device (here: serial ports)
> > to end a DMA transfer. To make this work, I need a signal from
> > exynos4210_uart.c to pl330.c to terminate the DMA after the receive
> > buffer is empty.
> >
> > How can I implement this in qemu ?
> That depends. How does the UART signal the DMA controller
> in real hardware? If there's a signal line of some kind,
> then you can model that with a qemu_irq line which the UART
> exposes and raises/lowers at the right time, that's then
> plumbed through by the SoC to the DMA controller.
Never mind my previous e-mail; the above was enough to get it working.


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