Re: [PATCH] PCI: dwc: Warn only for non-prefetchable memory resource size >4GB
From: Vidya Sagar
Date: Tue May 19 2020 - 13:08:50 EST
On 19-May-20 8:28 PM, Lorenzo Pieralisi wrote:
External email: Use caution opening links or attachments
On Tue, May 19, 2020 at 07:25:02PM +0530, Vidya Sagar wrote:
On 18-May-20 9:24 PM, Lorenzo Pieralisi wrote:
External email: Use caution opening links or attachments
On Wed, May 13, 2020 at 05:35:08PM -0500, Bjorn Helgaas wrote:
[+cc Alan; please cc authors of relevant commits,
updated Andrew's email address]
On Thu, May 14, 2020 at 12:38:55AM +0530, Vidya Sagar wrote:
commit 9e73fa02aa009 ("PCI: dwc: Warn if MEM resource size exceeds max for
32-bits") enables warning for MEM resources of size >4GB but prefetchable
memory resources also come under this category where sizes can go beyond
4GB. Avoid logging a warning for prefetchable memory resources.
Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx>
---
drivers/pci/controller/dwc/pcie-designware-host.c | 3 ++-
1 file changed, 2 insertions(+), 1 deletion(-)
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
?I think so. As I see from the code, ATU's
Region-0 is used for config space translation
Region-1 is used for non-prefetchable memory translation
Region-2 is used for I/O translation
So, there is no region reserved for translating prefetchable memory regions.
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 ?
Not Tegra driver but Tegra HW. Tegra HW doesn't need any ATU outbound
translation for prefetchable (for that matter any 1-to-1 mapping to
generate memory transactions on the PCIe bus).
The Warning is still valid for both Tegra and other DWC based
controllers for non-prefetchable memory translation.
Can DWC maintainers chime in and clarify please ?
prefetchable window and they can be greater than 4GB in size for all
right reasons. So, logging a warning for prefetchable region doesn't
seem correct to me. Please let me know if my understanding is wrong.
I think your patch is wrong and it is applied on top of a patch that
is wrong too, so I won't apply yours and it is likely I will revert
Alan's because it seems to solve nothing (and warn spuriously).
It is time for people who maintain DWC please to speak up because I
don't have the HW details required to make a judgment.
Lorenzo
- Vidya Sagar
Alan ? I want to understand what's the best course of action before
merging these patches.
Lorenzo