Re: [PATCH] hw/misc/edu: Rename macros indicating the direction of DMA operations

[Jason Chien <jason.chien@sifive.com>]

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This is a virtual device designed for educational purposes. The only spec I
found is in QEMU documentation:
https://github.com/qemu/qemu/blob/master/docs/specs/edu.rst
According to the documentation:
direction (0: from RAM to EDU, 1: from EDU to RAM)
The macros confused me and my goal is to make the direction easier to
differentiate. Something like EDU_DMA_TO_PCI_BUS and EDU_DMA_FROM_PCI_BUS
would also work. Do you have any suggestions?

thanks

Peter Maydell <peter.maydell@linaro.org> 於 2025年3月12日 週三 上午2:41寫道：

> On Thu, 27 Feb 2025 at 07:32, Jason Chien <jason.chien@sifive.com> wrote:
> >
> > This commit renames the macros to accurately reflect the direction of
> > DMA operations.
> >
> > EDU_DMA_TO_PCI now represents reading memory content into the EDU buffer,
> > while EDU_DMA_FROM_PCI represents writing EDU buffer content to memory.
>
> The EDU device is a PCI device, so if it is reading
> then it is reading data from the PCI bus, and if it is
> writing then it is writing data to the PCI bus. So I
> think there's an argument that the current names make
> sense.
>
> Plus, presumably this device model is implementing the hardware
> half of a defined specification. The authoritative source for
> what names the 0 and 1 values of the DIR bit should be named
> would be that specification.
>
> Where is that spec, and what does it say? If it says 0 for
> FROM and 1 for TO, that's what we should use. If it's the
> other way around, that's an error in our device implementation
> that we should correct.
>
> thanks
> -- PMM
>

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