On Mon, Feb 29, 2016 at 06:41:29AM -0800, Tim Harvey wrote: > On Wed, Feb 24, 2016 at 12:35 PM, Rob Herring <robh+dt@xxxxxxxxxx> wrote: > > 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 > > Rob, > > In this case I feel that every IMX6 based board with PCIe likely has > this issue because the original reference schematics from Freescale > did not mention that the LVDS clock source from the IMX6 did not meet > PCIe gen2 requirements so everyone blindly followed the reference > design. Only later did they seem to come out with this information and > if you did use an external clock you would have to setup the IMX6 pcie > clocks differently in the device-tree (configuring the IMX6 to use a > clock input instead of output), which I see no current boards doing. > > There are several SoC's that use the designware core that likely are > not in this same boat, so it would be unfair to penalize them by > defaulting a gen1 speed tied to the mac. So yes, perhaps a property of > the imx6 pcie phy and defaulting it to gen1 because no current > device-tree's set the phy's clock as an external input makes the most > sense? I'm not an IMX6 expert, but this sounds good to me, so I'll look for a new rev that does this. Bjorn -- 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
