On Tue, May 19, 2020 at 10:08:54PM +0000, Gustavo Pimentel wrote: [...] > > > > > > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c > > > > > > index 42fbfe2a1b8f..a29396529ea4 100644 > > > > > > --- a/drivers/pci/controller/dwc/pcie-designware-host.c > > > > > > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c > > > > > > @@ -366,7 +366,8 @@ int dw_pcie_host_init(struct pcie_port *pp) > > > > > > pp->mem = win->res; > > > > > > pp->mem->name = "MEM"; > > > > > > mem_size = resource_size(pp->mem); > > > > > > - if (upper_32_bits(mem_size)) > > > > > > + if (upper_32_bits(mem_size) && > > > > > > + !(win->res->flags & IORESOURCE_PREFETCH)) > > > > > > dev_warn(dev, "MEM resource size exceeds max for 32 bits\n"); > > > > > > pp->mem_size = mem_size; > > > > > > pp->mem_bus_addr = pp->mem->start - win->offset; > > > > > > > > That warning was added for a reason - why should not we log legitimate > > > > warnings ? AFAIU having resources larger than 4GB can lead to undefined > > > > behaviour given the current ATU programming API. > > > Yeah. I'm all for a warning if the size is larger than 4GB in case of > > > non-prefetchable window as one of the ATU outbound translation > > > channels is being used, > > > > Is it true for all DWC host controllers ? Or there may be another > > exception whereby we would be forced to disable this warning altogether > > ? > > > > > but, we are not employing any ATU outbound translation channel for > > > > What does this mean ? "we are not employing any ATU outbound...", is > > this the tegra driver ? And what guarantees that this warning is not > > legitimate on DWC host controllers that do use the ATU outbound > > translation for prefetchable windows ? > > > > Can DWC maintainers chime in and clarify please ? > > Before this code section, there is the following function call > pci_parse_request_of_pci_ranges(), which performs a simple validation for > the IORESOURCE_MEM resource type. > This validation checks if the resource is marked as prefetchable, if so, > an error message "non-prefetchable memory resource required" is given and > a return code with the -EINVAL value. That code checks if there is *at least* a non-prefetchable resource, that's all it does. > In other words, to reach the code that Vidya is changing, it can be only > if the resource is a non-prefetchable, any prefetchable resource will be > blocked by the previous call, if I'm not mistaken. I think you are mistaken sorry. > Having this in mind, Vidya's change will not make the expected result > aimed by him. I think Vidya's patch does what he expects, the question is whether it is widely applicable to ALL DWC hosts, that's what I want to know. > I don't see any problem by having resources larger than 4GB, from what > I'm seeing in the databook there isn't any restricting related to that as > long they don't consume the maximum space that is addressable by the > system (depending on if they are 32-bit or 64-bit system address). > > To be honest, I'm not seeing a system that could have this resource > larger than 4GB, but it might exist some exception that I don't know of, > that's why I accepted Alan's patch to warn the user that the resource > exceeds the maximum for the 32 bits so that he can be aware that he > *might* be consuming the maximum space addressable. I think it is most certainly a possibility to have > 4GB prefetchable address spaces so we ought to fix this for good. I still have to understand how the DWC host detects the memory region to be programmed into the ATU given that there is more than one but only 1 ATU memory region AFAICS. Lorenzo
