linux-kernel - Re: [PATCH v2 7/8] PCI: qcom: Add support for host_stop_link() & host_start

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Message-ID: <20240806191203.GA73014@bhelgaas>
Date: Tue, 6 Aug 2024 14:12:03 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: Krishna chaitanya chundru <quic_krichai@...cinc.com>
Cc: Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
	Krzysztof Kozlowski <krzk+dt@...nel.org>,
	Conor Dooley <conor+dt@...nel.org>,
	Konrad Dybcio <konrad.dybcio@...aro.org>,
	cros-qcom-dts-watchers@...omium.org,
	Bartosz Golaszewski <brgl@...ev.pl>,
	Jingoo Han <jingoohan1@...il.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	andersson@...nel.org, quic_vbadigan@...cinc.com,
	linux-arm-msm@...r.kernel.org, linux-pci@...r.kernel.org,
	devicetree@...r.kernel.org, linux-kernel@...r.kernel.org,
	Bartosz Golaszewski <bartosz.golaszewski@...aro.org>
Subject: Re: [PATCH v2 7/8] PCI: qcom: Add support for host_stop_link() &
 host_start_link()

On Sat, Aug 03, 2024 at 08:52:53AM +0530, Krishna chaitanya chundru wrote:
> For the switches like QPS615 which needs to configure it before
> the PCIe link is established.
> 
> if the link is not up assert the PERST# and disable LTSSM bit so
> that PCIe controller will not participate in the link training
> as part of host_stop_link().
> 
> De-assert the PERST# and enable LTSSM bit back in host_start_link().
> 
> Introduce ltssm_disable function op to stop the link training.

pcie-qcom.c is a driver for a PCIe host controller.  Apparently QPS615
is a switch in a hierarchy that could be below any PCIe host
controller, so I'm missing the connection with pcie-qcom.c.

Does this fix a problem that only occurs with pcie-qcom.c?  What
happens if you put a QPS615 below some other controller?

> Signed-off-by: Krishna chaitanya chundru <quic_krichai@...cinc.com>
> ---
>  drivers/pci/controller/dwc/pcie-qcom.c | 39 ++++++++++++++++++++++++++++++++++
>  1 file changed, 39 insertions(+)
> 
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 0180edf3310e..f4a6df53139c 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -233,6 +233,7 @@ struct qcom_pcie_ops {
>  	void (*host_post_init)(struct qcom_pcie *pcie);
>  	void (*deinit)(struct qcom_pcie *pcie);
>  	void (*ltssm_enable)(struct qcom_pcie *pcie);
> +	void (*ltssm_disable)(struct qcom_pcie *pcie);
>  	int (*config_sid)(struct qcom_pcie *pcie);
>  };
>  
> @@ -555,6 +556,41 @@ static int qcom_pcie_post_init_1_0_0(struct qcom_pcie *pcie)
>  	return 0;
>  }
>  
> +static int qcom_pcie_host_start_link(struct dw_pcie *pci)
> +{
> +	struct qcom_pcie *pcie = to_qcom_pcie(pci);
> +
> +	if (!dw_pcie_link_up(pcie->pci))  {
> +		qcom_ep_reset_deassert(pcie);
> +
> +		if (pcie->cfg->ops->ltssm_enable)
> +			pcie->cfg->ops->ltssm_enable(pcie);
> +	}
> +
> +	return 0;
> +}
> +
> +static void qcom_pcie_host_stop_link(struct dw_pcie *pci)
> +{
> +	struct qcom_pcie *pcie = to_qcom_pcie(pci);
> +
> +	if (!dw_pcie_link_up(pcie->pci))  {
> +		qcom_ep_reset_assert(pcie);
> +
> +		if (pcie->cfg->ops->ltssm_disable)
> +			pcie->cfg->ops->ltssm_disable(pcie);
> +	}
> +}
> +
> +static void qcom_pcie_2_3_2_ltssm_disable(struct qcom_pcie *pcie)
> +{
> +	u32 val;
> +
> +	val = readl(pcie->parf + PARF_LTSSM);
> +	val &= ~LTSSM_EN;
> +	writel(val, pcie->parf + PARF_LTSSM);
> +}
> +
>  static void qcom_pcie_2_3_2_ltssm_enable(struct qcom_pcie *pcie)
>  {
>  	u32 val;
> @@ -1306,6 +1342,7 @@ static const struct qcom_pcie_ops ops_1_9_0 = {
>  	.host_post_init = qcom_pcie_host_post_init_2_7_0,
>  	.deinit = qcom_pcie_deinit_2_7_0,
>  	.ltssm_enable = qcom_pcie_2_3_2_ltssm_enable,
> +	.ltssm_disable = qcom_pcie_2_3_2_ltssm_disable,
>  	.config_sid = qcom_pcie_config_sid_1_9_0,
>  };
>  
> @@ -1363,6 +1400,8 @@ static const struct qcom_pcie_cfg cfg_sc8280xp = {
>  static const struct dw_pcie_ops dw_pcie_ops = {
>  	.link_up = qcom_pcie_link_up,
>  	.start_link = qcom_pcie_start_link,
> +	.host_start_link = qcom_pcie_host_start_link,
> +	.host_stop_link = qcom_pcie_host_stop_link,
>  };
>  
>  static int qcom_pcie_icc_init(struct qcom_pcie *pcie)
> 
> -- 
> 2.34.1
>