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Message-ID: <r7cpjk2jun3h4xnfncqldeyfov4ad3bpq5kcfcxcx3eyg6g2hj@rcajqn7snemy>
Date: Fri, 12 Sep 2025 13:57:34 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: manivannan.sadhasivam@....qualcomm.com,
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 Mon, Sep 08, 2025 at 02:34:28PM GMT, Bjorn Helgaas wrote:
> 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"?
This is taken care now.
>
> > 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.
>
I've added a patch to fix in the next version of this series.
> > +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.
>
So I've introduced a new flag, qcom_pcie::legacy_binding, which gets set if the
driver uses qcom_pcie_parse_legacy_binding(). Based on this flag, PERST# will be
deasserted in this driver.
And I've removed references to 'new binding' term.
- Mani
--
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