linux-kernel - Re: [PATCH v6] mfd: Add support for RTS5250S power saving

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Date:   Thu, 14 Dec 2017 16:25:23 -0600
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     rui_feng@...lsil.com.cn
Cc:     lee.jones@...aro.org, linux-kernel@...r.kernel.org,
        Hans de Goede <hdegoede@...hat.com>,
        Dave Jiang <dave.jiang@...el.com>, linux-pci@...r.kernel.org
Subject: Re: [PATCH v6] mfd: Add support for RTS5250S power saving

[+cc Hans, Dave, linux-pci]

On Thu, Sep 07, 2017 at 04:26:39PM +0800, rui_feng@...lsil.com.cn wrote:
> From: Rui Feng <rui_feng@...lsil.com.cn>

I wish this had been posted to linux-pci before being merged.

I'm concerned because some of this appears to overlap and
conflict with PCI core management of ASPM.

I assume these devices advertise ASPM support in their Link
Capabilites registers, right?  If so, why isn't the existing
PCI core ASPM support sufficient?

> Enable power saving for RTS5250S as following steps:
> 1.Set 0xFE58 to enable clock power management.

Is this clock power management something specific to RTS5250S, or is
it standard PCIe architected stuff?

> 2.Check cfg space whether support L1SS or not.

This sounds like standard PCIe ASPM L1 Substates, right?

> 3.If support L1SS, set 0xFF03 to free clkreq.
> 4.When entering idle status, enable aspm
>   and set parameters for L1SS and LTR.
> 5.Wnen entering run status, disable aspm
>   and set parameters for L1SS and LTR.

In general, drivers should not configure ASPM, L1SS, and LTR
themselves; the PCI core should do that.

If a driver needs to tweak ASPM at run-time, it should use interfaces
exported by the PCI core to do so.

> If entering L1SS mode successfully,
> electric current will be below 2mA.

> Signed-off-by: Rui Feng <rui_feng@...lsil.com.cn>
> ...

> +static void rts5249_init_from_cfg(struct rtsx_pcr *pcr)
> +{
> +	struct rtsx_cr_option *option = &(pcr->option);
> +	u32 lval;
> +
> +	if (CHK_PCI_PID(pcr, PID_524A))
> +		rtsx_pci_read_config_dword(pcr,
> +			PCR_ASPM_SETTING_REG1, &lval);
> +	else
> +		rtsx_pci_read_config_dword(pcr,
> +			PCR_ASPM_SETTING_REG2, &lval);

This looks like you're reading the ASPM L1 Substates capability, i.e.,
PCI_L1SS_CAP, using hard-coded offsets based on the Device ID.  You
should be using pci_find_ext_capability() to locate it.

> +	if (lval & ASPM_L1_1_EN_MASK)
> +		rtsx_set_dev_flag(pcr, ASPM_L1_1_EN);
> +
> +	if (lval & ASPM_L1_2_EN_MASK)
> +		rtsx_set_dev_flag(pcr, ASPM_L1_2_EN);
> +
> +	if (lval & PM_L1_1_EN_MASK)
> +		rtsx_set_dev_flag(pcr, PM_L1_1_EN);
> +
> +	if (lval & PM_L1_2_EN_MASK)
> +		rtsx_set_dev_flag(pcr, PM_L1_2_EN);

You're adding these:

  #define ASPM_L1_1_EN_MASK              BIT(3)
  #define ASPM_L1_2_EN_MASK              BIT(2)
  #define PM_L1_1_EN_MASK                BIT(1)
  #define PM_L1_2_EN_MASK                BIT(0)

The PCI core already defines these and you should use them instead:

  #define  PCI_L1SS_CAP_PCIPM_L1_2        0x00000001  /* PCI-PM L1.2 Supported */
  #define  PCI_L1SS_CAP_PCIPM_L1_1        0x00000002  /* PCI-PM L1.1 Supported */
  #define  PCI_L1SS_CAP_ASPM_L1_2         0x00000004  /* ASPM L1.2 Supported */
  #define  PCI_L1SS_CAP_ASPM_L1_1         0x00000008  /* ASPM L1.1 Supported */

> +	if (option->ltr_en) {
> +		u16 val;
> +
> +		pcie_capability_read_word(pcr->pci, PCI_EXP_DEVCTL2, &val);
> +		if (val & PCI_EXP_DEVCTL2_LTR_EN) {
> +			option->ltr_enabled = true;
> +			option->ltr_active = true;

ltr_active is never actually used.

> +			rtsx_set_ltr_latency(pcr, option->ltr_active_latency);
> +		} else {
> +			option->ltr_enabled = false;
> +		}
> +	}
> +}
> ...

> +static void rts5249_set_aspm(struct rtsx_pcr *pcr, bool enable)
> +{
> +	struct rtsx_cr_option *option = &pcr->option;
> +	u8 val = 0;
> +
> +	if (pcr->aspm_enabled == enable)
> +		return;
> +
> +	if (option->dev_aspm_mode == DEV_ASPM_DYNAMIC) {
> +		if (enable)
> +			val = pcr->aspm_en;
> +		rtsx_pci_update_cfg_byte(pcr,
> +			pcr->pcie_cap + PCI_EXP_LNKCTL,
> +			ASPM_MASK_NEG, val);

This stomps on whatever ASPM configuration the PCI core did.

> +	} else if (option->dev_aspm_mode == DEV_ASPM_BACKDOOR) {

DEV_ASPM_BACKDOOR is never set, so this looks like dead code.

> +		u8 mask = FORCE_ASPM_VAL_MASK | FORCE_ASPM_CTL0;
> +		if (!enable)
> +			val = FORCE_ASPM_CTL0;
> +		rtsx_pci_write_register(pcr, ASPM_FORCE_CTL, mask, val);
> +	}
> +
> +	pcr->aspm_enabled = enable;
> +}