Re: [PATCH v3] PCI: rockchip: Increase the Max Credit update interval.

[Bjorn Helgaas <helgaas@kernel.org>]

On Thu, Sep 22, 2016 at 05:50:42PM -0700, Rajat Jain wrote:
> This increases the likelihood of link state to automatically go to L1
> and save some power.
> 
> The default credit update interval of 7.5 us results in the rootport
> sending UpdateFC-P and UpdateFC-NP packets too often, thus resulting
> in the link never going to L1, and always staying in L0/L0s. The
> value 24 us was chosen after some experiments and peeking over the
> PCIe bus to see that we do enter L1 substate when there is not enough
> traffic on the PCIe bus.
> 
> Signed-off-by: Rajat Jain <rajatja@google.com>

Applied with Shawn's ack to pci/host-rockchip for v4.9, thanks!

> ---
> v3: Fix the commit message.
> v2: Use the link bandwidth change irq to program the register.
> 
>  drivers/pci/host/pcie-rockchip.c | 17 +++++++++++++++++
>  1 file changed, 17 insertions(+)
> 
> diff --git a/drivers/pci/host/pcie-rockchip.c b/drivers/pci/host/pcie-rockchip.c
> index c3593e6..99e700f 100644
> --- a/drivers/pci/host/pcie-rockchip.c
> +++ b/drivers/pci/host/pcie-rockchip.c
> @@ -95,6 +95,11 @@
>  #define   PCIE_CORE_PL_CONF_SPEED_MASK		0x00000018
>  #define   PCIE_CORE_PL_CONF_LANE_MASK		0x00000006
>  #define   PCIE_CORE_PL_CONF_LANE_SHIFT		1
> +#define PCIE_CORE_TXCREDIT_CFG1		(PCIE_CORE_CTRL_MGMT_BASE + 0x020)
> +#define   PCIE_CORE_TXCREDIT_CFG1_MUI_MASK	0xFFFF0000
> +#define   PCIE_CORE_TXCREDIT_CFG1_MUI_SHIFT	16
> +#define   PCIE_CORE_TXCREDIT_CFG1_MUI_ENCODE(x) \
> +		(((x) >> 3) << PCIE_CORE_TXCREDIT_CFG1_MUI_SHIFT)
>  #define PCIE_CORE_INT_STATUS		(PCIE_CORE_CTRL_MGMT_BASE + 0x20c)
>  #define   PCIE_CORE_INT_PRFPE			BIT(0)
>  #define   PCIE_CORE_INT_CRFPE			BIT(1)
> @@ -224,6 +229,17 @@ static void rockchip_pcie_clr_bw_int(struct rockchip_pcie *rockchip)
>  	rockchip_pcie_write(rockchip, status, PCIE_RC_CONFIG_LCS);
>  }
>  
> +static void rockchip_pcie_update_txcredit_mui(struct rockchip_pcie *rockchip)
> +{
> +	u32 val;
> +
> +	/* Update Tx credit maximum update interval */
> +	val = rockchip_pcie_read(rockchip, PCIE_CORE_TXCREDIT_CFG1);
> +	val &= ~PCIE_CORE_TXCREDIT_CFG1_MUI_MASK;
> +	val |= PCIE_CORE_TXCREDIT_CFG1_MUI_ENCODE(24000);	/* ns */
> +	rockchip_pcie_write(rockchip, val, PCIE_CORE_TXCREDIT_CFG1);
> +}
> +
>  static int rockchip_pcie_valid_device(struct rockchip_pcie *rockchip,
>  				      struct pci_bus *bus, int dev)
>  {
> @@ -597,6 +613,7 @@ static irqreturn_t rockchip_pcie_subsys_irq_handler(int irq, void *arg)
>  		rockchip_pcie_write(rockchip, sub_reg, PCIE_CORE_INT_STATUS);
>  	} else if (reg & PCIE_CLIENT_INT_PHY) {
>  		dev_dbg(dev, "phy link changes\n");
> +		rockchip_pcie_update_txcredit_mui(rockchip);
>  		rockchip_pcie_clr_bw_int(rockchip);
>  	}
>  
> -- 
> 2.8.0.rc3.226.g39d4020
> 
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