On Wed, Feb 24, 2016 at 2:03 PM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: > [+cc Rob, devicetree list] > > On Wed, Dec 02, 2015 at 08:35:06AM -0800, Tim Harvey wrote: >> On Wed, Nov 25, 2015 at 3:14 PM, Bjorn Helgaas <helgaas@xxxxxxxxxx> wrote: >> > On Thu, Nov 19, 2015 at 06:12:45AM -0800, Tim Harvey wrote: >> >> Freescale has stated [1] that the LVDS clock source of the IMX6 does not pass >> >> the PCI Gen2 clock jitter test, therefore unless an external Gen2 compliant >> >> external clock source is present and supplied back to the IMX6 PCIe core >> >> via LVDS CLK1/CLK2 you can not claim Gen2 compliance. >> >> >> >> Add a dt property to specify gen1 vs gen2 and check this before allowing >> >> a Gen2 link. >> >> >> >> We default to Gen1 if the property is not present because at this time there >> >> are no IMX6 boards in mainline that 'input' a clock on LVDS CLK1/CLK2. >> >> >> >> In order to be Gen2 compliant on IMX6 you need to: >> >> - have a Gen2 compliant external clock generator and route that clock back >> >> to either LVDS CLK1 or LVDS CLK2 as an input. >> >> (see IMX6SX-SabreSD reference design) >> >> - specify this clock in the pcie node in the dt >> >> (ie IMX6QDL_CLK_LVDS1_IN or IMX6QDL_CLK_LVDS2_IN instead of >> >> IMX6QDL_CLK_LVDS1_GATE which configures it as a CLK output) >> >> >> >> [1] https://community.freescale.com/message/453209 >> >> >> >> Signed-off-by: Tim Harvey <tharvey@xxxxxxxxxxxxx> >> >> --- >> >> v2: >> >> - moved dt property to designware core >> >> >> >> .../devicetree/bindings/pci/designware-pcie.txt | 1 + >> >> drivers/pci/host/pci-imx6.c | 16 ++++++++++------ >> >> drivers/pci/host/pcie-designware.c | 4 ++++ >> >> drivers/pci/host/pcie-designware.h | 1 + >> >> 4 files changed, 16 insertions(+), 6 deletions(-) >> >> >> >> diff --git a/Documentation/devicetree/bindings/pci/designware-pcie.txt b/Documentation/devicetree/bindings/pci/designware-pcie.txt >> >> index 9f4faa8..a9a94b9 100644 >> >> --- a/Documentation/devicetree/bindings/pci/designware-pcie.txt >> >> +++ b/Documentation/devicetree/bindings/pci/designware-pcie.txt >> >> @@ -26,3 +26,4 @@ Optional properties: >> >> - bus-range: PCI bus numbers covered (it is recommended for new devicetrees to >> >> specify this property, to keep backwards compatibility a range of 0x00-0xff >> >> is assumed if not present) >> >> +- max-link-speed: Specify PCI gen for link capability (ie 2 for gen2) >> > >> > Is there some sort of DT or OF spec that lists "max-link-speed" as a >> > generic property? I see Lucas' desire to have this be common across >> > DesignWare PCIe cores. Should it be moved up a level even from there, >> > i.e., to bindings/pci/pci.txt? >> >> I don't know what the general consensus is here. As your the PCI >> maintainer I would leave that up to you. Are there other platforms >> that need to link at a lesser capability than the host controller is >> capable of? I am only aware of the IMX6 and SPEAr13XX [1] > > This is really a devicetree question, not a PCI one, so I added Rob > and the devicetree list in case they have any comments on this. Seems generally useful to me. You could want to limit the speed for a variety of reasons. There's no standard property that I'm aware of. Shouldn't this be a property of the phy though? >> > It might be worth mentioning in pci/fsl,imx6q-pcie.txt that we limit >> > the link to gen1 unless max-link-speed is present and has the value >> > "2". > > This default seems backwards. It seems like we'd want to configure > the link to go as fast as possible unless we have a quirk, e.g., > "max-link-speed", that imposes a device-specific link. In other > words, why don't we penalize the broken board instead of penalizing > all the working ones? I agree. It could be argued that this way doesn't require a DT update to fix broken boards. However, this problem should really be found before production and DT updates are normal for enabling new features (such as compliant PCIe). Rob -- To unsubscribe from this list: send the line "unsubscribe linux-pci" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
