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Message-ID: <20220224212811.GA291001@bhelgaas>
Date: Thu, 24 Feb 2022 15:28:11 -0600
From: Bjorn Helgaas <helgaas@...nel.org>
To: Pali Rohár <pali@...nel.org>
Cc: Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
Bjorn Helgaas <bhelgaas@...gle.com>,
Rob Herring <robh+dt@...nel.org>, Andrew Lunn <andrew@...n.ch>,
Thomas Petazzoni <thomas.petazzoni@...tlin.com>,
Krzysztof Wilczyński <kw@...ux.com>,
Marek Behún <kabel@...nel.org>,
Russell King <rmk+kernel@...linux.org.uk>,
Gregory Clement <gregory.clement@...tlin.com>,
linux-pci@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
linux-kernel@...r.kernel.org
Subject: Re: [PATCH 5/6] PCI: mvebu: Add support for sending
Set_Slot_Power_Limit message
On Tue, Feb 22, 2022 at 05:31:57PM +0100, Pali Rohár wrote:
> This PCIe message is sent automatically by mvebu HW when link changes
> status from down to up.
I *think* the intent of the above is:
If DT supplies the 'slot-power-limit-milliwatt' property, program
the value in the Slot Power Limit in the Slot Capabilities register
and program the Root Port to send a Set_Slot_Power_Limit Message
when the Link transitions to DL_Up.
PCIe r6.0, sec 2.2.8.5 and 7.5.3.9, also say Set_Slot_Power_Limit must
be sent on a config write to Slot Capabilities. I don't really
understand that, since AFAICS, everything in that register is
read-only. But there must be some use case for forcing a message.
> Slot power limit is read from DT property 'slot-power-limit-milliwatt' and
> set to mvebu HW. When this DT property is not specified then driver treat
> it as "Slot Capabilities register has not yet been initialized".
Does this last sentence mean "the Slot Power Limit is set to 0W
(Value = 00h and Scale = 00b = 1.0x) and Auto Slot Power Limit Disable
is set, so Set_Slot_Power_Limit Messages will never be sent"?
> Signed-off-by: Pali Rohár <pali@...nel.org>
> ---
> drivers/pci/controller/pci-mvebu.c | 85 ++++++++++++++++++++++++++++--
> 1 file changed, 80 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/pci/controller/pci-mvebu.c b/drivers/pci/controller/pci-mvebu.c
> index a75d2b9196f9..c786feec4d17 100644
> --- a/drivers/pci/controller/pci-mvebu.c
> +++ b/drivers/pci/controller/pci-mvebu.c
> @@ -66,6 +66,12 @@
> #define PCIE_STAT_BUS 0xff00
> #define PCIE_STAT_DEV 0x1f0000
> #define PCIE_STAT_LINK_DOWN BIT(0)
> +#define PCIE_SSPL_OFF 0x1a0c
> +#define PCIE_SSPL_VALUE_SHIFT 0
> +#define PCIE_SSPL_VALUE_MASK GENMASK(7, 0)
> +#define PCIE_SSPL_SCALE_SHIFT 8
> +#define PCIE_SSPL_SCALE_MASK GENMASK(9, 8)
> +#define PCIE_SSPL_ENABLE BIT(16)
> #define PCIE_RC_RTSTA 0x1a14
> #define PCIE_DEBUG_CTRL 0x1a60
> #define PCIE_DEBUG_SOFT_RESET BIT(20)
> @@ -111,6 +117,8 @@ struct mvebu_pcie_port {
> struct mvebu_pcie_window iowin;
> u32 saved_pcie_stat;
> struct resource regs;
> + u8 slot_power_limit_value;
> + u8 slot_power_limit_scale;
> struct irq_domain *intx_irq_domain;
> raw_spinlock_t irq_lock;
> int intx_irq;
> @@ -239,7 +247,7 @@ static void mvebu_pcie_setup_wins(struct mvebu_pcie_port *port)
>
> static void mvebu_pcie_setup_hw(struct mvebu_pcie_port *port)
> {
> - u32 ctrl, lnkcap, cmd, dev_rev, unmask;
> + u32 ctrl, lnkcap, cmd, dev_rev, unmask, sspl;
>
> /* Setup PCIe controller to Root Complex mode. */
> ctrl = mvebu_readl(port, PCIE_CTRL_OFF);
> @@ -292,6 +300,20 @@ static void mvebu_pcie_setup_hw(struct mvebu_pcie_port *port)
> /* Point PCIe unit MBUS decode windows to DRAM space. */
> mvebu_pcie_setup_wins(port);
>
> + /*
> + * Program Root Complex to automatically sends Set Slot Power Limit
> + * PCIe Message when changing status from Dl-Down to Dl-Up and valid
> + * slot power limit was specified.
s/Root Complex/Root Port/, right? AFAIK the message would be sent by
a Downstream Port, i.e., a Root Port in this case.
s/sends/send/
s/Set Slot Power Limit/Set_Slot_Power_Limit/ to match spec usage (also
below)
s/Dl-Down/DL_Down/ to match spec usage
s/Dl-Up/DL_Up/ ditto
> + */
> + sspl = mvebu_readl(port, PCIE_SSPL_OFF);
> + sspl &= ~(PCIE_SSPL_VALUE_MASK | PCIE_SSPL_SCALE_MASK | PCIE_SSPL_ENABLE);
> + if (port->slot_power_limit_value && port->slot_power_limit_scale) {
> + sspl |= port->slot_power_limit_value << PCIE_SSPL_VALUE_SHIFT;
> + sspl |= port->slot_power_limit_scale << PCIE_SSPL_SCALE_SHIFT;
> + sspl |= PCIE_SSPL_ENABLE;
> + }
> + mvebu_writel(port, sspl, PCIE_SSPL_OFF);
> +
> /* Mask all interrupt sources. */
> mvebu_writel(port, ~PCIE_INT_ALL_MASK, PCIE_INT_UNMASK_OFF);
>
> @@ -628,9 +650,16 @@ mvebu_pci_bridge_emul_pcie_conf_read(struct pci_bridge_emul *bridge,
> (PCI_EXP_LNKSTA_DLLLA << 16) : 0);
> break;
>
> - case PCI_EXP_SLTCTL:
> - *value = PCI_EXP_SLTSTA_PDS << 16;
> + case PCI_EXP_SLTCTL: {
> + u16 slotsta = le16_to_cpu(bridge->pcie_conf.slotsta);
> + u32 val = 0;
> + if (!(mvebu_readl(port, PCIE_SSPL_OFF) & PCIE_SSPL_ENABLE))
> + val |= PCI_EXP_SLTCTL_ASPL_DISABLE;
> + /* PCI_EXP_SLTCTL is 32-bit and contains also slot status bits */
This comment is a little bit confusing because PCI_EXP_SLTCTL is not
actually 32 bits; it's 16 bits. It's just that we "read" 32 bits,
which includes both PCI_EXP_SLTCTL and PCI_EXP_SLTSTA. If you use
"PCI_EXP_SLTCTL", I think it would be helpful to also say
"PCI_EXP_SLTSTA" instead of "slot status bits".
> + val |= slotsta << 16;
> + *value = val;
> break;
> + }
>
> case PCI_EXP_RTSTA:
> *value = mvebu_readl(port, PCIE_RC_RTSTA);
> @@ -774,6 +803,19 @@ mvebu_pci_bridge_emul_pcie_conf_write(struct pci_bridge_emul *bridge,
> mvebu_writel(port, new, PCIE_CAP_PCIEXP + PCI_EXP_LNKCTL);
> break;
>
> + case PCI_EXP_SLTCTL:
> + if ((mask & PCI_EXP_SLTCTL_ASPL_DISABLE) &&
> + port->slot_power_limit_value &&
> + port->slot_power_limit_scale) {
> + u32 sspl = mvebu_readl(port, PCIE_SSPL_OFF);
> + if (new & PCI_EXP_SLTCTL_ASPL_DISABLE)
> + sspl &= ~PCIE_SSPL_ENABLE;
> + else
> + sspl |= PCIE_SSPL_ENABLE;
> + mvebu_writel(port, sspl, PCIE_SSPL_OFF);
IIUC, the behavior of PCI_EXP_SLTCTL_ASPL_DISABLE as observed by
software that sets it and reads it back will depend on whether the DT
contains "slot-power-limit-milliwatt".
If there is no DT property, port->slot_power_limit_value will be zero
and PCIE_SSPL_ENABLE will never be set. So if I clear
PCI_EXP_SLTCTL_ASPL_DISABLE, then read it back, it looks like it will
read as being set. That's not what I would expect from the spec
(PCIe r6.0, sec 7.5.3.10).
> + }
> + break;
> +
> case PCI_EXP_RTSTA:
> /*
> * PME Status bit in Root Status Register (PCIE_RC_RTSTA)
> @@ -868,8 +910,26 @@ static int mvebu_pci_bridge_emul_init(struct mvebu_pcie_port *port)
> /*
> * Older mvebu hardware provides PCIe Capability structure only in
> * version 1. New hardware provides it in version 2.
> + * Enable slot support which is emulated.
> */
> - bridge->pcie_conf.cap = cpu_to_le16(pcie_cap_ver);
> + bridge->pcie_conf.cap = cpu_to_le16(pcie_cap_ver | PCI_EXP_FLAGS_SLOT);
> +
> + /*
> + * Set Presence Detect State bit permanently as there is no support for
> + * unplugging PCIe card from the slot. Assume that PCIe card is always
> + * connected in slot.
> + *
> + * Set physical slot number to port+1 as mvebu ports are indexed from
> + * zero and zero value is reserved for ports within the same silicon
> + * as Root Port which is not mvebu case.
> + *
> + * Also set correct slot power limit.
> + */
> + bridge->pcie_conf.slotcap = cpu_to_le32(
> + (port->slot_power_limit_value << PCI_EXP_SLTCAP_SPLV_SHIFT) |
> + (port->slot_power_limit_scale << PCI_EXP_SLTCAP_SPLS_SHIFT) |
> + ((port->port+1) << PCI_EXP_SLTCAP_PSN_SHIFT));
> + bridge->pcie_conf.slotsta = cpu_to_le16(PCI_EXP_SLTSTA_PDS);
>
> bridge->subsystem_vendor_id = ssdev_id & 0xffff;
> bridge->subsystem_id = ssdev_id >> 16;
> @@ -1191,6 +1251,7 @@ static int mvebu_pcie_parse_port(struct mvebu_pcie *pcie,
> {
> struct device *dev = &pcie->pdev->dev;
> enum of_gpio_flags flags;
> + u32 slot_power_limit;
> int reset_gpio, ret;
> u32 num_lanes;
>
> @@ -1291,6 +1352,15 @@ static int mvebu_pcie_parse_port(struct mvebu_pcie *pcie,
> port->reset_gpio = gpio_to_desc(reset_gpio);
> }
>
> + slot_power_limit = of_pci_get_slot_power_limit(child,
> + &port->slot_power_limit_value,
> + &port->slot_power_limit_scale);
> + if (slot_power_limit)
> + dev_info(dev, "%s: Slot power limit %u.%uW\n",
> + port->name,
> + slot_power_limit / 1000,
> + (slot_power_limit / 100) % 10);
> +
> port->clk = of_clk_get_by_name(child, NULL);
> if (IS_ERR(port->clk)) {
> dev_err(dev, "%s: cannot get clock\n", port->name);
> @@ -1587,7 +1657,7 @@ static int mvebu_pcie_remove(struct platform_device *pdev)
> {
> struct mvebu_pcie *pcie = platform_get_drvdata(pdev);
> struct pci_host_bridge *bridge = pci_host_bridge_from_priv(pcie);
> - u32 cmd;
> + u32 cmd, sspl;
> int i;
>
> /* Remove PCI bus with all devices. */
> @@ -1624,6 +1694,11 @@ static int mvebu_pcie_remove(struct platform_device *pdev)
> /* Free config space for emulated root bridge. */
> pci_bridge_emul_cleanup(&port->bridge);
>
> + /* Disable sending Set Slot Power Limit PCIe Message. */
> + sspl = mvebu_readl(port, PCIE_SSPL_OFF);
> + sspl &= ~(PCIE_SSPL_VALUE_MASK | PCIE_SSPL_SCALE_MASK | PCIE_SSPL_ENABLE);
> + mvebu_writel(port, sspl, PCIE_SSPL_OFF);
> +
> /* Disable and clear BARs and windows. */
> mvebu_pcie_disable_wins(port);
>
> --
> 2.20.1
>
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