On 2020-04-18 16:19, Gustavo Pimentel wrote:
Hi Marc and Alan,
I'm not convinced by this. If you know that, by construction, these
interrupts are not associated with an underlying MSI, why calling
get_cached_msi_msg() the first place?
There seem to be some assumptions in the DW EDMA driver that the
signaling would be MSI based, so maybe someone from Synopsys
(Gustavo?)
could clarify that. From my own perspective, running on an endpoint
device means that it is *generating* interrupts, and I'm not sure what
the MSIs represent here.
Giving a little context to this topic.
The eDMA IP present on the Synopsys DesignWare PCIe Endpoints can be
configured and triggered *remotely* as well *locally*.
For the sake of simplicity let's assume for now the eDMA was
implemented
on the EP and that is the IP that we want to configure and use.
When I say *remotely* I mean that this IP can be configurable through
the
RC/CPU side, however, for that, it requires the eDMA registers to be
exposed through a PCIe BAR on the EP. This will allow setting the SAR,
DAR and other settings, also need(s) the interrupt(s) address(es) to be
set as well (MSI or MSI-X only) so that it can signal through PCIe (to
the RC and consecutively the associated EP driver) if the data transfer
has been completed, aborted or if the Linked List consumer algorithm
has
passed in some linked element marked with a watermark.
It was based on this case that the eDMA driver was exclusively
developed.
However, Alan, wants to expand a little more this, by being able to use
this driver on the EP side (through
pcitest/pci_endpoint_test/pci_epf_test) so that he can configure this
IP
*locally*.
In fact, when doing this, he doesn't need to configure the interrupt
address (MSI or MSI-X), because this IP provides a local interrupt line
so that be connected to other blocks on the EP side.
Right, so this confirms my hunch that the driver is being used in
a way that doesn't reflect the expected use case. Rather than
papering over the problem by hacking the core code, I'd rather see
the eDMA driver be updated to support both host and endpoint cases.
This probably boils down to a PCI vs non-PCI set of helpers.
Alan, could you confirm whether we got it right?
Thanks,
M.
--
Jazz is not dead. It just smells funny...
