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Message-ID: <20250908193428.GA1437972@bhelgaas>
Date: Mon, 8 Sep 2025 14:34:28 -0500
From: Bjorn Helgaas <helgaas@...nel.org>
To: manivannan.sadhasivam@....qualcomm.com
Cc: Manivannan Sadhasivam <mani@...nel.org>,
Lorenzo Pieralisi <lpieralisi@...nel.org>,
Krzysztof Wilczyński <kwilczynski@...nel.org>,
Rob Herring <robh@...nel.org>, Bjorn Helgaas <bhelgaas@...gle.com>,
Bartosz Golaszewski <brgl@...ev.pl>,
Saravana Kannan <saravanak@...gle.com>, linux-pci@...r.kernel.org,
linux-arm-msm@...r.kernel.org, linux-kernel@...r.kernel.org,
devicetree@...r.kernel.org,
Krishna Chaitanya Chundru <krishna.chundru@....qualcomm.com>,
Brian Norris <briannorris@...omium.org>
Subject: Re: [PATCH v2 5/5] PCI: qcom: Allow pwrctrl core to toggle PERST#
for new DT binding
On Wed, Sep 03, 2025 at 12:43:27PM +0530, Manivannan Sadhasivam via B4 Relay wrote:
> If the platform is using the new DT binding, let the pwrctrl core toggle
> PERST# for the device. This is achieved by populating the
> 'pci_host_bridge::toggle_perst' callback with qcom_pcie_toggle_perst().
Can we say something here about how to identify a "new DT binding"?
I assume there is a DT property or something that makes it "new"?
> qcom_pcie_toggle_perst() will find the PERST# GPIO descriptor associated
> with the supplied 'device_node' and toggles PERST#. If PERST# is not found
> in the supplied node, the function will look for PERST# in the parent node
> as a fallback. This is needed since PERST# won't be available in the
> endpoint node as per the DT binding.
>
> Note that the driver still asserts PERST# during the controller
> initialization as it is needed as per the hardware documentation. Apart
> from that, the driver wouldn't touch PERST# for the new binding.
>
> Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@....qualcomm.com>
> ---
> drivers/pci/controller/dwc/pcie-qcom.c | 89 +++++++++++++++++++++++++++++-----
> 1 file changed, 78 insertions(+), 11 deletions(-)
>
> diff --git a/drivers/pci/controller/dwc/pcie-qcom.c b/drivers/pci/controller/dwc/pcie-qcom.c
> index 78355d12f10d263a0bb052e24c1e2d5e8f68603d..3c5c65d7d97cac186e1b671f80ba7296ad226d68 100644
> --- a/drivers/pci/controller/dwc/pcie-qcom.c
> +++ b/drivers/pci/controller/dwc/pcie-qcom.c
> @@ -276,6 +276,7 @@ struct qcom_pcie_port {
> struct qcom_pcie_perst {
> struct list_head list;
> struct gpio_desc *desc;
> + struct device_node *np;
> };
>
> struct qcom_pcie {
> @@ -298,11 +299,50 @@ struct qcom_pcie {
>
> #define to_qcom_pcie(x) dev_get_drvdata((x)->dev)
>
> -static void qcom_perst_assert(struct qcom_pcie *pcie, bool assert)
> +static struct gpio_desc *qcom_find_perst(struct qcom_pcie *pcie, struct device_node *np)
> +{
> + struct qcom_pcie_perst *perst;
> +
> + list_for_each_entry(perst, &pcie->perst, list) {
> + if (np == perst->np)
> + return perst->desc;
> + }
> +
> + return NULL;
> +}
> +
> +static void qcom_toggle_perst_per_device(struct qcom_pcie *pcie,
> + struct device_node *np, bool assert)
> +{
> + int val = assert ? 1 : 0;
> + struct gpio_desc *perst;
> +
> + perst = qcom_find_perst(pcie, np);
> + if (perst)
> + goto toggle_perst;
> +
> + /*
> + * If PERST# is not available in the current node, try the parent. This
> + * fallback is needed if the current node belongs to an endpoint or
> + * switch upstream port.
> + */
> + if (np->parent)
> + perst = qcom_find_perst(pcie, np->parent);
Ugh. I think we need to fix the data structures here before we go
much farther. We should be able to search for PERST# once at probe of
the Qcom controller. Hopefully we don't need lists of things.
See https://lore.kernel.org/r/20250908183325.GA1450728@bhelgaas.
> +toggle_perst:
> + /* gpiod* APIs handle NULL gpio_desc gracefully. So no need to check. */
> + gpiod_set_value_cansleep(perst, val);
> +}
> +
> +static void qcom_perst_reset(struct qcom_pcie *pcie, struct device_node *np,
> + bool assert)
> {
> struct qcom_pcie_perst *perst;
> int val = assert ? 1 : 0;
>
> + if (np)
> + return qcom_toggle_perst_per_device(pcie, np, assert);
> +
> if (list_empty(&pcie->perst))
> gpiod_set_value_cansleep(pcie->reset, val);
>
> @@ -310,22 +350,34 @@ static void qcom_perst_assert(struct qcom_pcie *pcie, bool assert)
> gpiod_set_value_cansleep(perst->desc, val);
> }
>
> -static void qcom_ep_reset_assert(struct qcom_pcie *pcie)
> +static void qcom_ep_reset_assert(struct qcom_pcie *pcie, struct device_node *np)
> {
> - qcom_perst_assert(pcie, true);
> + qcom_perst_reset(pcie, np, true);
> usleep_range(PERST_DELAY_US, PERST_DELAY_US + 500);
> }
>
> -static void qcom_ep_reset_deassert(struct qcom_pcie *pcie)
> +static void qcom_ep_reset_deassert(struct qcom_pcie *pcie,
> + struct device_node *np)
> {
> struct dw_pcie_rp *pp = &pcie->pci->pp;
>
> msleep(PCIE_T_PVPERL_MS);
> - qcom_perst_assert(pcie, false);
> + qcom_perst_reset(pcie, np, false);
> if (!pp->use_linkup_irq)
> msleep(PCIE_RESET_CONFIG_WAIT_MS);
> }
>
> +static void qcom_pcie_toggle_perst(struct pci_host_bridge *bridge,
> + struct device_node *np, bool assert)
> +{
> + struct qcom_pcie *pcie = dev_get_drvdata(bridge->dev.parent);
> +
> + if (assert)
> + qcom_ep_reset_assert(pcie, np);
> + else
> + qcom_ep_reset_deassert(pcie, np);
> +}
> +
> static int qcom_pcie_start_link(struct dw_pcie *pci)
> {
> struct qcom_pcie *pcie = to_qcom_pcie(pci);
> @@ -1320,7 +1372,7 @@ static int qcom_pcie_host_init(struct dw_pcie_rp *pp)
> struct qcom_pcie *pcie = to_qcom_pcie(pci);
> int ret;
>
> - qcom_ep_reset_assert(pcie);
> + qcom_ep_reset_assert(pcie, NULL);
>
> ret = pcie->cfg->ops->init(pcie);
> if (ret)
> @@ -1336,7 +1388,13 @@ static int qcom_pcie_host_init(struct dw_pcie_rp *pp)
> goto err_disable_phy;
> }
>
> - qcom_ep_reset_deassert(pcie);
> + /*
> + * Only deassert PERST# for all devices here if legacy binding is used.
> + * For the new binding, pwrctrl driver is expected to toggle PERST# for
> + * individual devices.
Can we replace "new binding" with something explicit? In a few
months, "new binding" won't mean anything.
> + */
> + if (list_empty(&pcie->perst))
> + qcom_ep_reset_deassert(pcie, NULL);
>
> if (pcie->cfg->ops->config_sid) {
> ret = pcie->cfg->ops->config_sid(pcie);
> @@ -1344,10 +1402,12 @@ static int qcom_pcie_host_init(struct dw_pcie_rp *pp)
> goto err_assert_reset;
> }
>
> + pci->pp.bridge->toggle_perst = qcom_pcie_toggle_perst;
> +
> return 0;
>
> err_assert_reset:
> - qcom_ep_reset_assert(pcie);
> + qcom_ep_reset_assert(pcie, NULL);
> err_disable_phy:
> qcom_pcie_phy_power_off(pcie);
> err_deinit:
> @@ -1361,7 +1421,7 @@ static void qcom_pcie_host_deinit(struct dw_pcie_rp *pp)
> struct dw_pcie *pci = to_dw_pcie_from_pp(pp);
> struct qcom_pcie *pcie = to_qcom_pcie(pci);
>
> - qcom_ep_reset_assert(pcie);
> + qcom_ep_reset_assert(pcie, NULL);
> qcom_pcie_phy_power_off(pcie);
> pcie->cfg->ops->deinit(pcie);
> }
> @@ -1740,6 +1800,9 @@ static int qcom_pcie_parse_perst(struct qcom_pcie *pcie,
> return -ENOMEM;
>
> perst->desc = reset;
> + /* Increase the refcount to make sure 'np' is valid till it is stored */
> + of_node_get(np);
> + perst->np = np;
> list_add_tail(&perst->list, &pcie->perst);
>
> parse_child_node:
> @@ -1803,8 +1866,10 @@ static int qcom_pcie_parse_ports(struct qcom_pcie *pcie)
> list_del(&port->list);
> }
>
> - list_for_each_entry_safe(perst, tmp_perst, &pcie->perst, list)
> + list_for_each_entry_safe(perst, tmp_perst, &pcie->perst, list) {
> + of_node_put(perst->np);
> list_del(&perst->list);
> + }
>
> return ret;
> }
> @@ -2044,8 +2109,10 @@ static int qcom_pcie_probe(struct platform_device *pdev)
> qcom_pcie_phy_exit(pcie);
> list_for_each_entry_safe(port, tmp_port, &pcie->ports, list)
> list_del(&port->list);
> - list_for_each_entry_safe(perst, tmp_perst, &pcie->perst, list)
> + list_for_each_entry_safe(perst, tmp_perst, &pcie->perst, list) {
> + of_node_put(perst->np);
> list_del(&perst->list);
> + }
> err_pm_runtime_put:
> pm_runtime_put(dev);
> pm_runtime_disable(dev);
>
> --
> 2.45.2
>
>
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