Subject: Re: [PATCH v3 2/4] PCI: layerscape: Add suspend/resume for ls1021a

From: Manivannan Sadhasivam <[email-masked]>
Date: Thu, 2 Nov 2023 22:58:09 +0530

On Tue, Oct 17, 2023 at 03:31:43PM -0400, Frank Li wrote:
> ls1021a add suspend/resume support.
> 
> Implement callback ls1021a_pcie_send_turnoff_msg(), which write scfg's
> SCFG_PEXPMWRCR to issue PME_Turn_off message.
> 
> Implement ls1021a_pcie_exit_from_l2() to let controller exit L2 state.
> 

I'd like to reword it to better reflect what the patch does:

"In the suspend path, PME_Turn_Off message is sent to the endpoint to transition
the link to L2/L3_Ready state. In this SoC, there is no way to check if the
controller has received the PME_To_Ack from the endpoint or not. So to be on the
safer side, the driver just waits for PCIE_PME_TO_L2_TIMEOUT_US before asserting
the SoC specific PMXMTTURNOFF bit to complete the PME_Turn_Off handshake. This
link would then enter L2/L3 state depending on the VAUX supply.

In the resume path, the link is brought back from L2 to L0 by doing a software
reset."

Although I do have questions on the resume behavior below.

> Signed-off-by: Frank Li <[email-masked]>
> ---
> 
> Notes:
>     Change from v2 to v3
>     - update according to mani's feedback
>     change from v1 to v2
>     - change subject 'a' to 'A'
> 
>  drivers/pci/controller/dwc/pci-layerscape.c | 86 ++++++++++++++++++++-
>  1 file changed, 85 insertions(+), 1 deletion(-)
> 
> diff --git a/drivers/pci/controller/dwc/pci-layerscape.c b/drivers/pci/controller/dwc/pci-layerscape.c
> index aea89926bcc4f..6f47cfe146c44 100644
> --- a/drivers/pci/controller/dwc/pci-layerscape.c
> +++ b/drivers/pci/controller/dwc/pci-layerscape.c
> @@ -35,11 +35,21 @@
>  #define PF_MCR_PTOMR		BIT(0)
>  #define PF_MCR_EXL2S		BIT(1)
>  
> +/* LS1021A PEXn PM Write Control Register */
> +#define SCFG_PEXPMWRCR(idx)	(0x5c + (idx) * 0x64)
> +#define PMXMTTURNOFF		BIT(31)
> +#define SCFG_PEXSFTRSTCR	0x190
> +#define PEXSR(idx)		BIT(idx)
> +
>  #define PCIE_IATU_NUM		6
>  
> +#define LS_PCIE_DRV_SCFG	BIT(0)
> +
>  struct ls_pcie_drvdata {
>  	const u32 pf_off;
> +	const struct dw_pcie_host_ops *ops;
>  	int (*exit_from_l2)(struct dw_pcie_rp *pp);
> +	int flags;

Why not "bool scfg_support"?

>  	bool pm_support;
>  };
>  
> @@ -47,6 +57,8 @@ struct ls_pcie {
>  	struct dw_pcie *pci;
>  	const struct ls_pcie_drvdata *drvdata;
>  	void __iomem *pf_base;
> +	struct regmap *scfg;
> +	int index;
>  	bool big_endian;
>  };
>  
> @@ -171,13 +183,65 @@ static int ls_pcie_host_init(struct dw_pcie_rp *pp)
>  	return 0;
>  }
>  
> +static void ls1021a_pcie_send_turnoff_msg(struct dw_pcie_rp *pp)
> +{
> +	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> +	struct ls_pcie *pcie = to_ls_pcie(pci);
> +	u32 val;
> +
> +	/* Send PME_Turn_Off message */
> +	regmap_read(pcie->scfg, SCFG_PEXPMWRCR(pcie->index), &val);
> +	val |= PMXMTTURNOFF;
> +	regmap_write(pcie->scfg, SCFG_PEXPMWRCR(pcie->index), val);
> +
> +	/*
> +	 * There is no specific register to check for PME_To_Ack from endpoint.
> +	 * So on the safe side, wait for PCIE_PME_TO_L2_TIMEOUT_US.
> +	 */
> +	mdelay(PCIE_PME_TO_L2_TIMEOUT_US/1000);
> +
> +	/*
> +	 * Layerscape hardware reference manual recommends clearing the PMXMTTURNOFF bit
> +	 * to complete the PME_Turn_Off handshake.
> +	 */
> +	regmap_read(pcie->scfg, SCFG_PEXPMWRCR(pcie->index), &val);
> +	val &= ~PMXMTTURNOFF;
> +	regmap_write(pcie->scfg, SCFG_PEXPMWRCR(pcie->index), val);
> +}
> +
> +static int ls1021a_pcie_exit_from_l2(struct dw_pcie_rp *pp)
> +{
> +	struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> +	struct ls_pcie *pcie = to_ls_pcie(pci);
> +	u32 val;
> +
> +	/* Only way exit from l2 is that do software reset */

So, what does exactly "software reset" mean? Are you resetting the endpoint or
some specific registers/blocks in the controller?

Also, what if the link goes to L3 in the case of no VAUX?

> +	regmap_read(pcie->scfg, SCFG_PEXSFTRSTCR, &val);
> +	val |= PEXSR(pcie->index);
> +	regmap_write(pcie->scfg, SCFG_PEXSFTRSTCR, val);
> +
> +	regmap_read(pcie->scfg, SCFG_PEXSFTRSTCR, &val);
> +	val &= ~PEXSR(pcie->index);
> +	regmap_write(pcie->scfg, SCFG_PEXSFTRSTCR, val);
> +
> +	return 0;
> +}
> +
>  static const struct dw_pcie_host_ops ls_pcie_host_ops = {
>  	.host_init = ls_pcie_host_init,
>  	.pme_turn_off = ls_pcie_send_turnoff_msg,
>  };
>  
> +static const struct dw_pcie_host_ops ls1021a_pcie_host_ops = {
> +	.host_init = ls_pcie_host_init,
> +	.pme_turn_off = ls1021a_pcie_send_turnoff_msg,
> +};
> +
>  static const struct ls_pcie_drvdata ls1021a_drvdata = {
> -	.pm_support = false,
> +	.pm_support = true,
> +	.ops = &ls1021a_pcie_host_ops,
> +	.exit_from_l2 = ls1021a_pcie_exit_from_l2,
> +	.flags = LS_PCIE_DRV_SCFG,
>  };
>  
>  static const struct ls_pcie_drvdata layerscape_drvdata = {
> @@ -205,6 +269,8 @@ static int ls_pcie_probe(struct platform_device *pdev)
>  	struct dw_pcie *pci;
>  	struct ls_pcie *pcie;
>  	struct resource *dbi_base;
> +	u32 index[2];
> +	int ret;
>  
>  	pcie = devm_kzalloc(dev, sizeof(*pcie), GFP_KERNEL);
>  	if (!pcie)
> @@ -220,6 +286,7 @@ static int ls_pcie_probe(struct platform_device *pdev)
>  	pci->pp.ops = &ls_pcie_host_ops;
>  
>  	pcie->pci = pci;
> +	pci->pp.ops = pcie->drvdata->ops ? pcie->drvdata->ops : &ls_pcie_host_ops;
>  
>  	dbi_base = platform_get_resource_byname(pdev, IORESOURCE_MEM, "regs");
>  	pci->dbi_base = devm_pci_remap_cfg_resource(dev, dbi_base);
> @@ -230,6 +297,23 @@ static int ls_pcie_probe(struct platform_device *pdev)
>  
>  	pcie->pf_base = pci->dbi_base + pcie->drvdata->pf_off;
>  
> +	if (pcie->drvdata->flags & LS_PCIE_DRV_SCFG) {
> +

Remove extra newline.

- Mani

-- 
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