[+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. > > 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? > [1] http://git.kernel.org/cgit/linux/kernel/git/torvalds/linux.git/tree/Documentation/devicetree/bindings/pci/spear13xx-pcie.txt#n14 -- 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
