[PATCH v3] PCI: rockchip: Add quirk to disable RC's ASPM L0s

Bjorn Helgaas helgaas at kernel.org
Thu Jan 12 13:57:40 PST 2017

On Thu, Jan 12, 2017 at 09:53:17AM +0800, Shawn Lin wrote:
> Rockchip's RC outputs 100MHz reference clock but there are
> two methods for PHY to generate it.
> (1)One of them is to use system PLL to generate 100MHz clock and
> the PHY will relock it and filter signal noise then outputs the
> reference clock.
> (2)Another way is to share Soc's 24MHZ crystal oscillator with
> PHY and force PHY's DLL to generate 100MHz internally.
> When using case(2), the exit from L0s doesn't work fine occasionally
> due to the broken design of RC receiver's logical circuit. So even if
> we use extended-synch, it still fails for PHY to relock the bits from
> FTS sometimes. This will hang the system.
> Maybe we could argue that why not use case(1) to avoid it? The reason
> is that as we could see the reference clock is derived from system PLL
> and the path from it to PHY isn't so clean which means there are some
> noise introduced by power-domain and other buses can't be filterd out
> by PHY and we could see noise from the frequency spectrum by
> oscilloscope. This makes the TX compatibility test a little difficult
> to pass the spec. So case(1) and case(2) are both used indeed now. If
> using case(2), we should disable RC's L0s support, and that is why we
> need this property to indicate this quirk.
> Also after checking quirk.c, I noticed there is already a quirk for
> disabling L0s unconditionally, quirk_disable_aspm_l0s. But obviously we
> shouldn't do that as mentioned above that case(1) could still works fine
> with L0s.
> Reported-by: Jeffy Chen <jeffy.chen at rock-chips.com>
> Cc: Brian Norris <briannorris at chromium.org>
> Signed-off-by: Shawn Lin <shawn.lin at rock-chips.com>

I applied this to pci/host-rockchip for v4.11.  I added Brian's Reviewed-by
and Rob's Acked-by, since you didn't change anything substantive.

I assume there's no way to automatically discover whether the system is
using the 24MHz oscillator?  If there is a way, we should use that instead
of requiring a DT property.

I reworded the changelog; I hope it still make sense:

    PCI: rockchip: Disable RC's ASPM L0s based on DT "aspm-no-l0s"
    Rockchip's RC produces a 100MHz reference clock but there are two methods
    for the PHY to generate it:
      (1) Use the system PLL to generate a 100MHz clock.  The PHY will relock
          it, filter signal noise, and output the reference clock.  ASPM L0s
          works correctly, but circuit noise issues make it difficult to pass
	  the TX compatibility test.
      (2) Share the SoC's 24MHZ crystal oscillator with the PHY and force the
          PHY's PLL to generate 100MHz internally.  In this case, exit from
          ASPM L0s sometimes fails due to a design error in the RC receiver
          circuit.  Even if we use extended-synch, the PHY sometimes fails to
          relock the bits from FTS, which will hang the system.
    We want the flexibility to use both clocking methods, so add a DT property,
    "aspm-no-l0s".  If that's present, disable L0s to avoid the issues with
    case (2).
    [bhelgaas: changelog]
    Reported-by: Jeffy Chen <jeffy.chen at rock-chips.com>
    Signed-off-by: Shawn Lin <shawn.lin at rock-chips.com>
    Signed-off-by: Bjorn Helgaas <bhelgaas at google.com>
    Reviewed-by: Brian Norris <briannorris at chromium.org>
    Acked-by: Rob Herring <robh at kernel.org>

> ---
> Changes in v3:
> - fix misspelled aspm for the property name
> Changes in v2:
> - drop the quirk prefix
>  Documentation/devicetree/bindings/pci/rockchip-pcie.txt | 2 ++
>  drivers/pci/host/pcie-rockchip.c                        | 9 +++++++++
>  2 files changed, 11 insertions(+)
> diff --git a/Documentation/devicetree/bindings/pci/rockchip-pcie.txt b/Documentation/devicetree/bindings/pci/rockchip-pcie.txt
> index 71aeda1..1453a73 100644
> --- a/Documentation/devicetree/bindings/pci/rockchip-pcie.txt
> +++ b/Documentation/devicetree/bindings/pci/rockchip-pcie.txt
> @@ -43,6 +43,8 @@ Required properties:
>  - interrupt-map-mask and interrupt-map: standard PCI properties
>  Optional Property:
> +- aspm-no-l0s: RC won't support ASPM L0s. This property is needed if
> +	using 24MHz OSC for RC's PHY.
>  - ep-gpios: contain the entry for pre-reset gpio
>  - num-lanes: number of lanes to use
>  - vpcie3v3-supply: The phandle to the 3.3v regulator to use for PCIe.
> diff --git a/drivers/pci/host/pcie-rockchip.c b/drivers/pci/host/pcie-rockchip.c
> index f2dca7b..140cdc7 100644
> --- a/drivers/pci/host/pcie-rockchip.c
> +++ b/drivers/pci/host/pcie-rockchip.c
> @@ -140,6 +140,8 @@
>  #define   PCIE_RC_CONFIG_DCR_CSPL_LIMIT		0xff
> +#define   PCIE_RC_CONFIG_LINK_CAP_L0S		BIT(10)
> @@ -653,6 +655,13 @@ static int rockchip_pcie_init_port(struct rockchip_pcie *rockchip)
>  	rockchip_pcie_write(rockchip, status, PCIE_RC_CONFIG_THP_CAP);
> +	/* Clear L0s from RC's link cap */
> +	if (of_property_read_bool(dev->of_node, "aspm-no-l0s")) {
> +		status = rockchip_pcie_read(rockchip, PCIE_RC_CONFIG_LINK_CAP);
> +		status &= ~PCIE_RC_CONFIG_LINK_CAP_L0S;
> +		rockchip_pcie_write(rockchip, status, PCIE_RC_CONFIG_LINK_CAP);
> +	}
> +
>  	rockchip_pcie_write(rockchip, 0x0, PCIE_RC_BAR_CONF);
>  	rockchip_pcie_write(rockchip,
> -- 
> 1.9.1
> --
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