Re: [PATCH v3 5/6] PCI: qcom: Add support for host_stop_link() & host_start_link()

[Krishna Chaitanya Chundru]

On 11/15/2024 5:27 PM, Manivannan Sadhasivam wrote:
> On Tue, Nov 12, 2024 at 08:31:37PM +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 up, the boatloader might powered and configured the
> > endpoint/switch already. In that case don't touch PCIe link else
> > 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.
> >
> > Signed-off-by: Krishna chaitanya chundru <quic_krichai@xxxxxxxxxxx>
> > ---
> >   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 ef44a82be058..048aea94e319 100644
> > --- a/drivers/pci/controller/dwc/pcie-qcom.c
> > +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> > @@ -246,6 +246,7 @@ 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);
> >   };
> >   
> > @@ -617,6 +618,41 @@ 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))  {
>
> I don't think the controller driver should worry about the bootloader
> initialization. You should export dw_pcie_link_up() as a callback and call
> start/stop link if only required (link not up) from the pwrctl driver.
Instead of exporting this API, I will try to read config space and see 
if the link is up or not. if it is not up then will call these.

- Krishna Chaitanya.

> - Mani
>
> > +		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;
> > @@ -1361,6 +1397,7 @@ 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,
> >   };
> >   
> > @@ -1418,6 +1455,8 @@ 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