Message-ID: <20230731133637.GC6436@thinkpad>
Date:   Mon, 31 Jul 2023 19:06:37 +0530
From:   Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>
To:     Frank Li <Frank.li@....com>
Cc:     lorenzo.pieralisi@....com, bhelgaas@...gle.com,
        devicetree@...r.kernel.org, gustavo.pimentel@...opsys.com,
        helgaas@...nel.org, imx@...ts.linux.dev, kw@...ux.com,
        leoyang.li@....com, linux-arm-kernel@...ts.infradead.org,
        linux-imx@....com, linux-kernel@...r.kernel.org,
        linux-pci@...r.kernel.org, mani@...nel.org, minghuan.lian@....com,
        mingkai.hu@....com, robh+dt@...nel.org, roy.zang@....com,
        shawnguo@...nel.org, zhiqiang.hou@....com
Subject: Re: [PATCH v5 1/2] PCI: dwc: Implement general suspend/resume
 functionality for L2/L3 transitionse

On Fri, Jul 28, 2023 at 11:49:28AM -0400, Frank Li wrote:
> On Fri, Jul 28, 2023 at 09:02:38PM +0530, Manivannan Sadhasivam wrote:
> > On Mon, Jul 24, 2023 at 05:58:29PM -0400, Frank Li wrote:
> > > Introduced helper function dw_pcie_get_ltssm to retrieve SMLH_LTSS_STATE.
> > > Added API pme_turn_off and exit_from_l2 for managing L2/L3 state transitions.
> > > 
> > > Typical L2 entry workflow:
> > > 
> > > 1. Transmit PME turn off signal to PCI devices and wait for PME_To_Ack.
> > > 2. Await link entering L2_IDLE state.
> > > 3. Transition Root complex to D3 state.
> > > 
> > > Typical L2 exit workflow:
> > > 
> > > 1. Transition Root complex to D0 state.
> > > 2. Issue exit from L2 command.
> > > 3. Reinitialize PCI host.
> > > 4. Wait for link to become active.
> > > 
> > > Signed-off-by: Frank Li <Frank.Li@....com>
> > > ---
> > > Change from v4 to v5:
> > > - Closes: https://lore.kernel.org/oe-kbuild-all/202307211904.zExw4Q8H-lkp@intel.com/
> > > Change from v3 to v4:
> > > - change according to Manivannan's comments.
> > >   I hope I have not missed anything. quite long discuss thread
> > > Change from v2 to v3:
> > > - Basic rewrite whole patch according rob herry suggestion.
> > >   put common function into dwc, so more soc can share the same logic.
> > > 
> > >  .../pci/controller/dwc/pcie-designware-host.c | 95 +++++++++++++++++++
> > >  drivers/pci/controller/dwc/pcie-designware.h  | 28 ++++++
> > >  2 files changed, 123 insertions(+)
> > > 
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware-host.c b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > index 9952057c8819..031e1f9c0d0c 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware-host.c
> > > +++ b/drivers/pci/controller/dwc/pcie-designware-host.c
> > > @@ -8,6 +8,7 @@
> > >   * Author: Jingoo Han <jg1.han@...sung.com>
> > >   */
> > >  
> > > +#include <linux/iopoll.h>
> > >  #include <linux/irqchip/chained_irq.h>
> > >  #include <linux/irqdomain.h>
> > >  #include <linux/msi.h>
> > > @@ -807,3 +808,97 @@ int dw_pcie_setup_rc(struct dw_pcie_rp *pp)
> > >  	return 0;
> > >  }
> > >  EXPORT_SYMBOL_GPL(dw_pcie_setup_rc);
> > > +
> > > +/*
> > > + * This resemble the pci_set_power_state() interfaces, but these are for
> > 
> > s/interfaces/API
> > s/these are/this is
> > 
> > > + * configuring host controllers, which are bridges *to* PCI devices but
> > > + * are not PCI devices themselves.
> > > + */
> > > +static void dw_pcie_set_dstate(struct dw_pcie *pci, pci_power_t dstate)
> > > +{
> > > +	u8 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_PM);
> > > +	u16 val;
> > > +
> > > +	val = dw_pcie_readw_dbi(pci, offset + PCI_PM_CTRL);
> > > +	val &= ~PCI_PM_CTRL_STATE_MASK;
> > > +	val |= ((u16 __force)dstate) & PCI_PM_CTRL_STATE_MASK;
> > 
> > Why can't just,
> > 
> > val |= dstate;
> 
> fixed a build warning.
> 
> Closes: https://lore.kernel.org/oe-kbuild-all/202307211904.zExw4Q8H-lkp@intel.com/
> 

Ah ok. Missed this report. But still you can get rid of the mask part.

> > 
> > > +	dw_pcie_writew_dbi(pci, offset + PCI_PM_CTRL, val);
> > > +}
> > > +
> > > +int dw_pcie_suspend_noirq(struct dw_pcie *pci)
> > > +{
> > > +	u8 offset;
> > > +	u32 val;
> > > +	int ret;
> > > +
> > > +	offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);
> > 
> > Just assign this during variable definition itself..
> 
> Do you means?
> 	u8 offset = dw_pcie_find_capability(pci, PCI_CAP_ID_EXP);

Yes!

> > 
> > > +	/*
> > > +	 * If L1.1\L1.2 enable, devices (such as NVME) want short
> > > +	 * resume latency, controller will not enter L2
> > 
> > "If L1SS is supported, then do not put the link into L2 as some devices such as
> > NVMe expect low resume latency."
> > 
> > > +	 */
> > > +	if (dw_pcie_readw_dbi(pci, offset + PCI_EXP_LNKCTL) & PCI_EXP_LNKCTL_ASPM_L1)
> > > +		return 0;
> > > +
> > > +	if (dw_pcie_get_ltssm(pci) <= DW_PCIE_LTSSM_DETECT_ACT)
> > > +		return 0;
> > > +
> > > +	if (!pci->pp.ops->pme_turn_off)
> > > +		return -EINVAL;
> > 
> > Can you just return 0 instead of failing? As per my comment below, if you move
> > the D-state change before this callback, then this won't be a hard requirement.
> > 
> > > +
> > > +	pci->pp.ops->pme_turn_off(&pci->pp);
> > > +
> > > +	/*
> > > +	 * PCI Express Base Specification Rev 4.0
> > > +	 * 5.3.3.2.1 PME Synchronization
> > > +	 * Recommand 1ms to 10ms timeout to check L2 ready
> > 
> > "Recommends"
> > 
> > Please use full 80 columns for comments.
> > 
> > > +	 */
> > > +	ret = read_poll_timeout(dw_pcie_get_ltssm, val, val == DW_PCIE_LTSSM_L2_IDLE,
> > > +				100, 10000, false, pci);
> > > +	if (ret) {
> > > +		dev_err(pci->dev, "PCIe link enter L2 timeout! ltssm = 0x%x\n", val);
> > 
> > "Timeout waiting for L2 entry! LTSSM: 0x%x\n"
> > 
> > > +		return ret;
> > > +	}
> > > +
> > > +	dw_pcie_set_dstate(pci, PCI_D3hot);
> > 
> > This should be done before initiating L2 entry as per
> > PCI_Express_Base_Specification 3.0, section 5.2.
> 
> This is for root complex bridge, after PCI device and link to L2,
> PCI Host can be enter lower power state, I think it is just
> borrow 'D3 state' from PCI.
> 

This is confusing now. What is the behavior if the root complex changes D-state
but the device driver expects a different one? For instance, during suspend, the
NVMe driver expects the D-state to be D0 only [1] not to be changed by the PCI
core. This might apply to other drivers as well.

Better to leave the D-state change to PCI core itself.

- Mani

[1] https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/drivers/nvme/host/pci.c#n3218

> > 
> > > +
> > > +	pci->suspended = true;
> > > +
> > > +	return ret;
> > > +}
> > > +EXPORT_SYMBOL_GPL(dw_pcie_suspend_noirq);
> > > +
> > > +int dw_pcie_resume_noirq(struct dw_pcie *pci)
> > > +{
> > > +	int ret;
> > > +
> > > +	if (!pci->suspended)
> > > +		return 0;
> > > +
> > > +	pci->suspended = false;
> > > +
> > > +	dw_pcie_set_dstate(pci, PCI_D0);
> > > +
> > > +	if (!pci->pp.ops->exit_from_l2)
> > > +		return -EINVAL;
> > 
> > Same comment as above.
> > 
> > > +
> > > +	pci->pp.ops->exit_from_l2(&pci->pp);
> > > +
> > > +	ret = pci->pp.ops->host_init(&pci->pp);
> > 
> > I don't see matching host_deinit() in suspend.
> > 
> > - Mani
> > 
> > > +	if (ret) {
> > > +		dev_err(pci->dev, "Host init failed! ret = 0x%x\n", ret);
> > > +		return ret;
> > > +	}
> > > +
> > > +	dw_pcie_setup_rc(&pci->pp);
> > > +
> > > +	ret = dw_pcie_start_link(pci);
> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	ret = dw_pcie_wait_for_link(pci);
> > > +	if (ret)
> > > +		return ret;
> > > +
> > > +	return ret;
> > > +}
> > > +EXPORT_SYMBOL_GPL(dw_pcie_resume_noirq);
> > > diff --git a/drivers/pci/controller/dwc/pcie-designware.h b/drivers/pci/controller/dwc/pcie-designware.h
> > > index 79713ce075cc..effb07a506e4 100644
> > > --- a/drivers/pci/controller/dwc/pcie-designware.h
> > > +++ b/drivers/pci/controller/dwc/pcie-designware.h
> > > @@ -288,10 +288,21 @@ enum dw_pcie_core_rst {
> > >  	DW_PCIE_NUM_CORE_RSTS
> > >  };
> > >  
> > > +enum dw_pcie_ltssm {
> > > +	DW_PCIE_LTSSM_UNKNOWN = 0xFFFFFFFF,
> > > +	/* Need align PCIE_PORT_DEBUG0 bit0:5 */
> > 
> > "Need to align with PCIE_PORT_DEBUG0 bits 0:5".
> > 
> > - Mani
> > 
> > > +	DW_PCIE_LTSSM_DETECT_QUIET = 0x0,
> > > +	DW_PCIE_LTSSM_DETECT_ACT = 0x1,
> > > +	DW_PCIE_LTSSM_L0 = 0x11,
> > > +	DW_PCIE_LTSSM_L2_IDLE = 0x15,
> > > +};
> > > +
> > >  struct dw_pcie_host_ops {
> > >  	int (*host_init)(struct dw_pcie_rp *pp);
> > >  	void (*host_deinit)(struct dw_pcie_rp *pp);
> > >  	int (*msi_host_init)(struct dw_pcie_rp *pp);
> > > +	void (*pme_turn_off)(struct dw_pcie_rp *pp);
> > > +	void (*exit_from_l2)(struct dw_pcie_rp *pp);
> > >  };
> > >  
> > >  struct dw_pcie_rp {
> > > @@ -364,6 +375,7 @@ struct dw_pcie_ops {
> > >  	void    (*write_dbi2)(struct dw_pcie *pcie, void __iomem *base, u32 reg,
> > >  			      size_t size, u32 val);
> > >  	int	(*link_up)(struct dw_pcie *pcie);
> > > +	enum dw_pcie_ltssm (*get_ltssm)(struct dw_pcie *pcie);
> > >  	int	(*start_link)(struct dw_pcie *pcie);
> > >  	void	(*stop_link)(struct dw_pcie *pcie);
> > >  };
> > > @@ -393,6 +405,7 @@ struct dw_pcie {
> > >  	struct reset_control_bulk_data	app_rsts[DW_PCIE_NUM_APP_RSTS];
> > >  	struct reset_control_bulk_data	core_rsts[DW_PCIE_NUM_CORE_RSTS];
> > >  	struct gpio_desc		*pe_rst;
> > > +	bool			suspended;
> > >  };
> > >  
> > >  #define to_dw_pcie_from_pp(port) container_of((port), struct dw_pcie, pp)
> > > @@ -430,6 +443,9 @@ void dw_pcie_iatu_detect(struct dw_pcie *pci);
> > >  int dw_pcie_edma_detect(struct dw_pcie *pci);
> > >  void dw_pcie_edma_remove(struct dw_pcie *pci);
> > >  
> > > +int dw_pcie_suspend_noirq(struct dw_pcie *pci);
> > > +int dw_pcie_resume_noirq(struct dw_pcie *pci);
> > > +
> > >  static inline void dw_pcie_writel_dbi(struct dw_pcie *pci, u32 reg, u32 val)
> > >  {
> > >  	dw_pcie_write_dbi(pci, reg, 0x4, val);
> > > @@ -501,6 +517,18 @@ static inline void dw_pcie_stop_link(struct dw_pcie *pci)
> > >  		pci->ops->stop_link(pci);
> > >  }
> > >  
> > > +static inline enum dw_pcie_ltssm dw_pcie_get_ltssm(struct dw_pcie *pci)
> > > +{
> > > +	u32 val;
> > > +
> > > +	if (pci->ops && pci->ops->get_ltssm)
> > > +		return pci->ops->get_ltssm(pci);
> > > +
> > > +	val = dw_pcie_readl_dbi(pci, PCIE_PORT_DEBUG0);
> > > +
> > > +	return (enum dw_pcie_ltssm)FIELD_GET(PORT_LOGIC_LTSSM_STATE_MASK, val);
> > > +}
> > > +
> > >  #ifdef CONFIG_PCIE_DW_HOST
> > >  irqreturn_t dw_handle_msi_irq(struct dw_pcie_rp *pp);
> > >  int dw_pcie_setup_rc(struct dw_pcie_rp *pp);
> > > -- 
> > > 2.34.1
> > > 
> > 
> > -- 
> > மணிவண்ணன் சதாசிவம்

-- 
மணிவண்ணன் சதாசிவம்

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