On Fri, Nov 10, 2017 at 12:11:05AM +0530, Vidya Sagar wrote: > > > On Thursday 09 November 2017 11:44 PM, Bjorn Helgaas wrote: > > [+cc Lorenzo] > > > > On Thu, Nov 09, 2017 at 12:48:14PM +0530, Vidya Sagar wrote: > > > On Thursday 09 November 2017 02:55 AM, Bjorn Helgaas wrote: > > > > On Mon, Nov 06, 2017 at 11:33:07PM +0530, Vidya Sagar wrote: > > > > > limits MSI target address to only 32-bit region to enable > > > > > some of the PCIe end points where only 32-bit MSIs > > > > > are supported work properly. > > > > > One example being Marvel SATA controller > > > > > > > > > > Signed-off-by: Vidya Sagar <vidyas@xxxxxxxxxx> > > > > > --- > > > > > drivers/pci/host/pci-tegra.c | 2 +- > > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > > > diff --git a/drivers/pci/host/pci-tegra.c b/drivers/pci/host/pci-tegra.c > > > > > index 1987fec1f126..03d3dcdd06c2 100644 > > > > > --- a/drivers/pci/host/pci-tegra.c > > > > > +++ b/drivers/pci/host/pci-tegra.c > > > > > @@ -1531,7 +1531,7 @@ static int tegra_pcie_enable_msi(struct tegra_pcie *pcie) > > > > > } > > > > > /* setup AFI/FPCI range */ > > > > > - msi->pages = __get_free_pages(GFP_KERNEL, 0); > > > > > + msi->pages = __get_free_pages(GFP_DMA, 0); > > > > > msi->phys = virt_to_phys((void *)msi->pages); > > > > Should this be GFP_DMA32? See the comment above the GFP_DMA > > > > definition. > > > looking at the comments for both GFP_DMA32 and GFP_DMA, I thought GFP_DMA32 > > > is the correct one to use, but, even with that I got >32-bit addresses. > > > GFP_DMA always gives addresses in <4GB boundary (i.e. 32-bit). > > > I didn't dig into it to find out why is this the case. > > This sounds worth looking into (but maybe we don't need the > > __get_free_pages() at all; see below). Maybe there's some underlying > > bug. My laptop shows this, which looks like it might be related: > > > > Zone ranges: > > DMA [mem 0x0000000000001000-0x0000000000ffffff] > > DMA32 [mem 0x0000000001000000-0x00000000ffffffff] > > Normal [mem 0x0000000100000000-0x00000004217fffff] > > Device empty > > > > What does your machine show? > I see following in my linux box > Zone ranges: > DMA [mem 0x0000000000001000-0x0000000000ffffff] > DMA32 [mem 0x0000000001000000-0x00000000ffffffff] > Normal [mem 0x0000000100000000-0x000000106effffff] > Device empty > > and following in my T210 Tegra platform > Zone ranges: > DMA [mem 0x0000000080000000-0x00000000ffffffff] > Normal [mem 0x0000000100000000-0x000000017fffffff] This seems to be happening because 64-bit ARM doesn't have the ZONE_DMA32 Kconfig option, which seems to cause the DMA32 zone to default to the normal zone (see include/linux/gfp.h). That's very confusing in conjunction with the kerneldoc comment for GFP_DMA32 because it isn't actually guaranteed to give you 32-bit addresses for !ZONE_DMA32. Cc'ing Arnd who knows about these things. Thierry
Attachment:
signature.asc
Description: PGP signature
