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

From: Peter Maydell
Subject: Re: How to tell DMA controller in qemu to terminate transfer ?
Date: Fri, 10 Jan 2020 10:36:20 +0000

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.

-- PMM

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