Re: [PATCH] pci_dma_rw: return correct value instead of 0

[Peter Maydell]

On Thu, 30 Jul 2020 at 08:42, Stefano Garzarella <sgarzare@redhat.com> wrote:
> I agree that it is better to return the dma_memory_rw() return value, but
> at first look, no one seems to check the return value of pci_dma_rw(),
> pci_dma_read(), andpci_dma_write().
>
> Should we make them void?

In general code (eg device models) that issues memory transactions
need to have a mechanism for finding out whether the transaction
succeeds. Traditionally QEMU didn't have the concept of a
transaction failing, but we have added it, starting with the
APIs at the bottom level (the address_space_* ones). We haven't
always plumbed the error-handling (or the memory-transaction
input, for that matter) through to some of these other APIs.
I think for consistency we should do that, and ideally we
should make all these APIs look the same as the base-level
address_space* ones, which would mean returning a MemTxError
rather than a bool.

We should also figure out why the dma_* functions exist at all:
they include some calls to dma_barrier(), but not all devices
do DMA with the dma_* functions, so we have an inconsistency
that should be sorted out...

thanks
-- PMM