Subject: Re: [PATCH 05/10] dt-bindings: PCI: tegra: Add device tree support for T194

From: Thierry Reding <[email-masked]>
Date: Thu, 28 Mar 2019 14:15:08 +0100

On Tue, Mar 26, 2019 at 08:43:22PM +0530, Vidya Sagar wrote:
> Add support for Tegra194 PCIe controllers. These controllers are based
> on Synopsys DesignWare core IP.
> 
> Signed-off-by: Vidya Sagar <[email-masked]>
> ---
>  .../bindings/pci/nvidia,tegra194-pcie.txt          | 209 +++++++++++++++++++++
>  .../devicetree/bindings/phy/phy-tegra194-p2u.txt   |  34 ++++
>  2 files changed, 243 insertions(+)
>  create mode 100644 Documentation/devicetree/bindings/pci/nvidia,tegra194-pcie.txt
>  create mode 100644 Documentation/devicetree/bindings/phy/phy-tegra194-p2u.txt
> 
> diff --git a/Documentation/devicetree/bindings/pci/nvidia,tegra194-pcie.txt b/Documentation/devicetree/bindings/pci/nvidia,tegra194-pcie.txt
> new file mode 100644
> index 000000000000..31527283a0cd
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/pci/nvidia,tegra194-pcie.txt
> @@ -0,0 +1,209 @@
> +NVIDIA Tegra PCIe controller (Synopsys DesignWare Core based)
> +
> +This PCIe host controller is based on the Synopsis Designware PCIe IP
> +and thus inherits all the common properties defined in designware-pcie.txt.
> +
> +Required properties:
> +- compatible: For Tegra19x, must contain "nvidia,tegra194-pcie".
> +- device_type: Must be "pci"
> +- reg: A list of physical base address and length for each set of controller
> +  registers. Must contain an entry for each entry in the reg-names property.
> +- reg-names: Must include the following entries:
> +  "appl": Controller's application logic registers
> +  "window1": This is the aperture of controller available under 4GB boundary
> +             (i.e. within 32-bit space). This aperture is typically used for
> +             accessing config space of root port itself and also the connected
> +             endpoints (by appropriately programming internal Address
> +             Translation Unit's (iATU) out bound region) and also to map
> +             prefetchable/non-prefetchable BARs.
> +  "config": As per the definition in designware-pcie.txt

I see that you set this to a 256 KiB region for all controllers. Since
each function can have up to 4 KiB of extended configuration space, that
means you have space to address:

    256 KiB = 4 KiB * 8 functions * 8 devices

Each bus can have up to 32 devices (including the root port) and there
can be 256 busses, so I wonder how this is supposed to work. How does
the mapping work for configuration space? Does the controller allow
moving this 256 KiB window around so that more devices' configuration
space can be accessed?

> +  "atu_dma": iATU and DMA register. This is where the iATU (internal Address
> +             Translation Unit) registers of the PCIe core are made available
> +             fow SW access.
> +  "dbi": The aperture where root port's own configuration registers are
> +         available

This is slightly confusing because you already said in the description
of "window1" that it is used to access the configuration space of the
root port itself.

Is the root port configuration space available via the regular
configuration space registers?

> +  "window2": This is the larger (compared to window1) aperture available above
> +             4GB boundary (i.e. in 64-bit space). This is typically used for
> +             mapping prefetchable/non-prefetchable BARs of endpoints
> +- interrupts: A list of interrupt outputs of the controller. Must contain an
> +  entry for each entry in the interrupt-names property.
> +- interrupt-names: Must include the following entries:
> +  "intr": The Tegra interrupt that is asserted for controller interrupts
> +  "msi": The Tegra interrupt that is asserted when an MSI is received
> +- bus-range: Range of bus numbers associated with this controller
> +- #address-cells: Address representation for root ports (must be 3)
> +  - cell 0 specifies the bus and device numbers of the root port:
> +    [23:16]: bus number
> +    [15:11]: device number
> +  - cell 1 denotes the upper 32 address bits and should be 0
> +  - cell 2 contains the lower 32 address bits and is used to translate to the
> +    CPU address space
> +- #size-cells: Size representation for root ports (must be 2)
> +- ranges: Describes the translation of addresses for root ports and standard
> +  PCI regions. The entries must be 7 cells each, where the first three cells
> +  correspond to the address as described for the #address-cells property
> +  above, the fourth and fifth cells are for the physical CPU address to
> +  translate to and the sixth and seventh cells are as described for the
> +  #size-cells property above.
> +  - Entries setup the mapping for the standard I/O, memory and
> +    prefetchable PCI regions. The first cell determines the type of region
> +    that is setup:
> +    - 0x81000000: I/O memory region
> +    - 0x82000000: non-prefetchable memory region
> +    - 0xc2000000: prefetchable memory region
> +  Please refer to the standard PCI bus binding document for a more detailed
> +  explanation.
> +- #interrupt-cells: Size representation for interrupts (must be 1)
> +- interrupt-map-mask and interrupt-map: Standard PCI IRQ mapping properties
> +  Please refer to the standard PCI bus binding document for a more detailed
> +  explanation.
> +- clocks: Must contain an entry for each entry in clock-names.
> +  See ../clocks/clock-bindings.txt for details.
> +- clock-names: Must include the following entries:
> +  - core_clk

It's redundant to name a clock _clk. Is this already required by the
standard Designware bindings or is this new?

> +- resets: Must contain an entry for each entry in reset-names.
> +  See ../reset/reset.txt for details.
> +- reset-names: Must include the following entries:
> +  - core_apb_rst
> +  - core_rst

Same comment as for clock-names.

> +- phys: Must contain a phandle to P2U PHY for each entry in phy-names.
> +- phy-names: Must include an entry for each active lane.
> +  "pcie-p2u-N": where N ranges from 0 to one less than the total number of lanes

I'd leave away the "pcie-" prefix since the surrounding context already
makes it clear that this is for PCIe.

> +- Controller dependent register offsets
> +  - nvidia,event-cntr-ctrl: EVENT_COUNTER_CONTROL reg offset
> +      0x168 - FPGA
> +      0x1a8 - C1, C2 and C3
> +      0x1c4 - C4
> +      0x1d8 - C0 and C5
> +  - nvidia,event-cntr-data: EVENT_COUNTER_DATA reg offset
> +      0x16c - FPGA
> +      0x1ac - C1, C2 and C3
> +      0x1c8 - C4
> +      0x1dc - C0 and C5
> +- nvidia,controller-id : Controller specific ID
> +      0x0 - C0
> +      0x1 - C1
> +      0x2 - C2
> +      0x3 - C3
> +      0x4 - C4
> +      0x5 - C5

It's redundant to have both a controller ID and parameterized register
offsets based on that controller ID. I would recommend keeping the
controller ID and then moving the register offsets to the driver and
decide based on the controller ID.

> +- vddio-pex-ctl-supply: Regulator supply for PCIe side band signals
> +
> +Optional properties:
> +- nvidia,max-speed: limits controllers max speed to this value.
> +    1 - Gen-1 (2.5 GT/s)
> +    2 - Gen-2 (5 GT/s)
> +    3 - Gen-3 (8 GT/s)
> +    4 - Gen-4 (16 GT/s)
> +- nvidia,init-speed: limits controllers init speed to this value.
> +    1 - Gen-1 (2. 5 GT/s)
> +    2 - Gen-2 (5 GT/s)
> +    3 - Gen-3 (8 GT/s)
> +    4 - Gen-4 (16 GT/s)
> +- nvidia,disable-aspm-states : controls advertisement of ASPM states
> +    bit-0 to '1' : disables advertisement of ASPM-L0s
> +    bit-1 to '1' : disables advertisement of ASPM-L1. This also disables
> +                 advertisement of ASPM-L1.1 and ASPM-L1.2
> +    bit-2 to '1' : disables advertisement of ASPM-L1.1
> +    bit-3 to '1' : disables advertisement of ASPM-L1.2

These seem more like configuration options rather than hardware
description.

> +- nvidia,disable-clock-request : gives a hint to driver that there is no
> +    CLKREQ signal routing on board
> +- nvidia,update-fc-fixup : needs it to improve perf when a platform is designed
> +    in such a way that it satisfies at least one of the following conditions
> +    1. If C0/C4/C5 run at x1/x2 link widths (irrespective of speed and MPS)
> +    2. If C0/C1/C2/C3/C4/C5 operate at their respective max link widths and
> +       a) speed is Gen-2 and MPS is 256B
> +       b) speed is >= Gen-3 with any MPS

If we know these conditions, can we not determine that the fixup is
needed at runtime?

> +- nvidia,cdm-check : Enables CDM checking. For more information, refer Synopsis
> +    DesignWare Cores  PCI Express Controller Databook r4.90a Chapter S.4

Why should this be configurable through device tree?

> +- nvidia,enable-power-down : Enables power down of respective controller and
> +    corresponding PLLs if they are not shared by any other entity

Wouldn't we want this to be the default? Why keep things powered up if
they are not needed?

> +- "nvidia,pex-wake" : Add PEX_WAKE gpio number to provide wake support.
> +- "nvidia,plat-gpios" : Add gpio number that needs to be configured before
> +   system goes for enumeration. There could be platforms where enabling 3.3V and
> +   12V power supplies are done through GPIOs, in which case, list of all such
> +   GPIOs can be specified through this property.

For power supplies we usually use the regulator bindings. Are there any
other cases where we'd need this?

> +- "nvidia,aspm-cmrt" : Common Mode Restore time for proper operation of ASPM to
> +   be specified in microseconds
> +- "nvidia,aspm-pwr-on-t" : Power On time for proper operation of ASPM to be
> +   specified in microseconds
> +- "nvidia,aspm-l0s-entrance-latency" : ASPM L0s entrance latency to be specified
> +   in microseconds
> +
> +Examples:
> +=========
> +
> +Tegra194:
> +--------
> +
> +SoC DTSI:
> +
> +	pcie@14180000 {
> +		compatible = "nvidia,tegra194-pcie", "snps,dw-pcie";

It doesn't seem to me like claiming compatibility with "snps,dw-pcie" is
correct. There's a bunch of NVIDIA- or Tegra-specific properties below
and code in the driver. Would this device be able to function if no
driver was binding against the "nvidia,tegra194-pcie" compatible string?
Would it work if you left that out? I don't think so, so we should also
not list it here.

> +		power-domains = <&bpmp TEGRA194_POWER_DOMAIN_PCIEX8B>;
> +		reg = <0x00 0x14180000 0x0 0x00020000   /* appl registers (128K)      */
> +		       0x00 0x38000000 0x0 0x00040000   /* configuration space (256K) */
> +		       0x00 0x38040000 0x0 0x00040000>; /* iATU_DMA reg space (256K)  */
> +		reg-names = "appl", "config", "atu_dma";
> +
> +		status = "disabled";
> +
> +		#address-cells = <3>;
> +		#size-cells = <2>;
> +		device_type = "pci";
> +		num-lanes = <8>;
> +		linux,pci-domain = <0>;
> +
> +		clocks = <&bpmp TEGRA194_CLK_PEX0_CORE_0>;
> +		clock-names = "core_clk";
> +
> +		resets = <&bpmp TEGRA194_RESET_PEX0_CORE_0_APB>,
> +			 <&bpmp TEGRA194_RESET_PEX0_CORE_0>;
> +		reset-names = "core_apb_rst", "core_rst";
> +
> +		interrupts = <GIC_SPI 72 IRQ_TYPE_LEVEL_HIGH>,	/* controller interrupt */
> +			     <GIC_SPI 73 IRQ_TYPE_LEVEL_HIGH>;	/* MSI interrupt */
> +		interrupt-names = "intr", "msi";
> +
> +		#interrupt-cells = <1>;
> +		interrupt-map-mask = <0 0 0 0>;
> +		interrupt-map = <0 0 0 0 &gic 0 72 0x04>;
> +
> +		nvidia,bpmp = <&bpmp>;
> +
> +		nvidia,max-speed = <4>;
> +		nvidia,disable-aspm-states = <0xf>;
> +		nvidia,controller-id = <&bpmp 0x0>;

Why is there a reference to the BPMP in this propert?

> +		nvidia,aux-clk-freq = <0x13>;
> +		nvidia,preset-init = <0x5>;

aux-clk-freq and preset-init are not defined in the binding above.

> +		nvidia,aspm-cmrt = <0x3C>;
> +		nvidia,aspm-pwr-on-t = <0x14>;
> +		nvidia,aspm-l0s-entrance-latency = <0x3>;

These should be in decimal notation to make them easier to deal with. I
don't usually read time in hexadecimal.

> +
> +		bus-range = <0x0 0xff>;
> +		ranges = <0x81000000 0x0 0x38100000 0x0 0x38100000 0x0 0x00100000      /* downstream I/O (1MB) */
> +			  0x82000000 0x0 0x38200000 0x0 0x38200000 0x0 0x01E00000      /* non-prefetchable memory (30MB) */
> +			  0xc2000000 0x18 0x00000000 0x18 0x00000000 0x4 0x00000000>;  /* prefetchable memory (16GB) */
> +
> +		nvidia,cfg-link-cap-l1sub = <0x1c4>;
> +		nvidia,cap-pl16g-status = <0x174>;
> +		nvidia,cap-pl16g-cap-off = <0x188>;
> +		nvidia,event-cntr-ctrl = <0x1d8>;
> +		nvidia,event-cntr-data = <0x1dc>;
> +		nvidia,dl-feature-cap = <0x30c>;

These are not defined in the binding above.

> +	};
> +
> +Board DTS:
> +
> +	pcie@14180000 {
> +		status = "okay";
> +
> +		vddio-pex-ctl-supply = <&vdd_1v8ao>;
> +
> +		phys = <&p2u_2>,
> +		       <&p2u_3>,
> +		       <&p2u_4>,
> +		       <&p2u_5>;
> +		phy-names = "pcie-p2u-0", "pcie-p2u-1", "pcie-p2u-2",
> +			    "pcie-p2u-3";
> +	};
> diff --git a/Documentation/devicetree/bindings/phy/phy-tegra194-p2u.txt b/Documentation/devicetree/bindings/phy/phy-tegra194-p2u.txt

Might be better to split this into a separate patch.

> new file mode 100644
> index 000000000000..cc0de8e8e8db
> --- /dev/null
> +++ b/Documentation/devicetree/bindings/phy/phy-tegra194-p2u.txt
> @@ -0,0 +1,34 @@
> +NVIDIA Tegra194 P2U binding
> +
> +Tegra194 has two PHY bricks namely HSIO (High Speed IO) and NVHS (NVIDIA High
> +Speed) each interfacing with 12 and 8 P2U instances respectively.
> +A P2U instance is a glue logic between Synopsys DesignWare Core PCIe IP's PIPE
> +interface and PHY of HSIO/NVHS bricks. Each P2U instance represents one PCIe
> +lane.
> +
> +Required properties:
> +- compatible: For Tegra19x, must contain "nvidia,tegra194-phy-p2u".

Isn't the "phy-" implied by "p2u"? The name of the hardware block is
"Tegra194 P2U", so that "phy-" seems gratuitous to me.

> +- reg: Should be the physical address space and length of respective each P2U
> +       instance.
> +- reg-names: Must include the entry "base".

"base" is a bad name. Each of these entries will be a "base" of the
given region. The name should specify what region it is the base of.

Thierry

> +
> +Required properties for PHY port node:
> +- #phy-cells: Defined by generic PHY bindings.  Must be 0.
> +
> +Refer to phy/phy-bindings.txt for the generic PHY binding properties.
> +
> +Example:
> +
> +hsio-p2u {
> +	compatible = "simple-bus";
> +	#address-cells = <2>;
> +	#size-cells = <2>;
> +	ranges;
> +	p2u_0: p2u@03e10000 {
> +		compatible = "nvidia,tegra194-phy-p2u";
> +		reg = <0x0 0x03e10000 0x0 0x00010000>;
> +		reg-names = "base";
> +
> +		#phy-cells = <0>;
> +	};
> +}
> -- 
> 2.7.4
> 
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