Re: [PATCH 1/2] OF/PCI: Export inbound memory interface to PCI RC drivers.

[Bjorn Helgaas <helgaas@kernel.org>]

[-cc Oza, bounced]

On Mon, Sep 30, 2019 at 11:46:18PM +0200, Marek Vasut wrote:
> On 9/30/19 11:40 PM, Bjorn Helgaas wrote:
> > This would follow the convention for subject lines:
> > 
> >   PCI: OF: Add of_pci_get_dma_ranges() for inbound DMA restrictions
> > 
> > On Fri, Aug 09, 2019 at 07:34:48PM +0200 wrote:
> >> From: Oza Pawandeep
> >>
> >> The patch exports interface to PCIe RC drivers so that,
> >> Drivers can get their inbound memory configuration.
> > 
> > IIUC this interface (of_pci_get_dma_ranges()) is not used directly by
> > *drivers*; it is used by of_bus_pci_get_dma_ranges() in the next
> > patch, and it's called by the driver core via this path:
> > 
> >   really_probe
> >     pci_dma_configure                     # pci_bus_type.dma_configure
> >       of_dma_configure
> > 	of_dma_get_range
> > 	  bus->get_dma_ranges
> > 	    of_bus_pci_get_dma_ranges     # of_busses[0].get_dma_ranges
> > 	      of_pci_get_dma_ranges
> > 
> >> It provides basis for IOVA reservations for inbound memory
> >> holes, if RC is not capable of addressing all the host memory,
> >> Specifically when IOMMU is enabled and on ARMv8 where 64bit IOVA
> >> could be allocated.
> >>
> >> It handles multiple inbound windows, and returns resources,
> >> and is left to the caller, how it wants to use them.
> > 
> > This should say exactly what the problem is, maybe even with a link to
> > a problem report.  I assume it is something like "RC <X> cannot
> > address all of host memory, and if we happen to allocate a buffer
> > that's not addressable, DMA to the buffer fails".  It'd be nice to
> > know what the failure looks like (SERR# asserted, panic, reboot, etc).
> 
> [...]
> 
> While it's good that someone finally looked at these patches, these were
> since superseded by the following series:
> https://patchwork.ozlabs.org/cover/1168166/

Good to know, thanks :)