Re: [PATCH v2 2/5] PCI: stm32: Add PCIe host support for STM32MP25

Manivannan Sadhasivam
2024-12-18T09:52:27Z

On Mon, Dec 16, 2024 at 10:00:27AM +0100, Christian Bruel wrote:

[...]

> >
> > > + msleep(PCIE_T_RRS_READY_MS);
> > > +
> > > + return ret;
> > > +}
> > > +
> > > +static void stm32_pcie_stop_link(struct dw_pcie *pci)
> > > +{
> > > + struct stm32_pcie *stm32_pcie = to_stm32_pcie(pci);
> > > +
> > > + regmap_update_bits(stm32_pcie->regmap, SYSCFG_PCIECR,
> > > + STM32MP25_PCIECR_LTSSM_EN, 0);
> > > +
> > > + /* Assert PERST# */
> > > + if (stm32_pcie->perst_gpio)
> > > + gpiod_set_value(stm32_pcie->perst_gpio, 1);
> >
> > I don't like tying PERST# handling with start/stop link. PERST# should be
> > handled based on the power/clock state.
>
> I don't understand your point: We turn off the PHY in suspend_noirq(), so
> that seems a logical place to de-assert in resume_noirq after the refclk is
> ready. PERST# should be kept active until the PHY stablilizes the clock in
> resume. From the PCIe electromechanical specs, PERST# goes active while the
> refclk is not stable/
>

While your understanding about PERST# is correct, your implementation is not.
You are toggling PERST# from start/stop link callbacks which are supposed to
control the LTSSM state only. I don't have issues with toggling PERST# in
stm32_pcie_{suspend/resume}_noirq().

>
> >
> > > +}
> > > +
> > > +static int stm32_pcie_suspend(struct device *dev)
> > > +{
> > > + struct stm32_pcie *stm32_pcie = dev_get_drvdata(dev);
> > > +
> > > + if (device_may_wakeup(dev) || device_wakeup_path(dev))
> > > + enable_irq_wake(stm32_pcie->wake_irq);
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +static int stm32_pcie_resume(struct device *dev)
> > > +{
> > > + struct stm32_pcie *stm32_pcie = dev_get_drvdata(dev);
> > > +
> > > + if (device_may_wakeup(dev) || device_wakeup_path(dev))
> > > + disable_irq_wake(stm32_pcie->wake_irq);
> > > +
> > > + return 0;
> > > +}
> > > +
> > > +static int stm32_pcie_suspend_noirq(struct device *dev)
> > > +{
> > > + struct stm32_pcie *stm32_pcie = dev_get_drvdata(dev);
> > > +
> > > + stm32_pcie->link_is_up = dw_pcie_link_up(stm32_pcie->pci);
> > > +
> > > + stm32_pcie_stop_link(stm32_pcie->pci);
> >
> > I don't understand how endpoint can wakeup the host if PERST# gets asserted.
>
> The stm32 PCIe doesn't support L2, we don't expect an in-band beacon for the
> wakeup. We support wakeup only from sideband WAKE#, that will restart the
> link from IRQ
>

I don't understand how WAKE# is supported without L2. Only in L2 state, endpoint
will make use of Vaux and it will wakeup the host using either beacon or WAKE#.
If you don't support L2, then the endpoint will reach L3 (link off) state.

> >
> > > + clk_disable_unprepare(stm32_pcie->clk);
> > > +
> > > + if (!device_may_wakeup(dev) && !device_wakeup_path(dev))
> > > + phy_exit(stm32_pcie->phy);
> > > +
> > > + return pinctrl_pm_select_sleep_state(dev);
> > > +}
> > > +
> > > +static int stm32_pcie_resume_noirq(struct device *dev)
> > > +{
> > > + struct stm32_pcie *stm32_pcie = dev_get_drvdata(dev);
> > > + struct dw_pcie *pci = stm32_pcie->pci;
> > > + struct dw_pcie_rp *pp = &pci->pp;
> > > + int ret;
> > > +
> > > + /* init_state must be called first to force clk_req# gpio when no
> >
> > CLKREQ#
> >
> > Why RC should control CLKREQ#?
>
> REFCLK is gated with CLKREQ#, So we cannot access the core
> without CLKREQ# if no device is present. So force it with a init pinmux
> the time to init the PHY and the core DBI registers
>

Ok. You should add a comment to clarify it in the code as this is not a standard
behavior.

> >
> > Also please use preferred style for multi-line comments:
> >
> > /*
> > * ...
> > */
> >
> > > + * device is plugged.
> > > + */
> > > + if (!IS_ERR(dev->pins->init_state))
> > > + ret = pinctrl_select_state(dev->pins->p, dev->pins->init_state);
> > > + else
> > > + ret = pinctrl_pm_select_default_state(dev);
> > > +
> > > + if (ret) {
> > > + dev_err(dev, "Failed to activate pinctrl pm state: %d\n", ret);
> > > + return ret;
> > > + }
> > > +
> > > + if (!device_may_wakeup(dev) && !device_wakeup_path(dev)) {
> > > + ret = phy_init(stm32_pcie->phy);
> > > + if (ret) {
> > > + pinctrl_pm_select_default_state(dev);
> > > + return ret;
> > > + }
> > > + }
> > > +
> > > + ret = clk_prepare_enable(stm32_pcie->clk);
> > > + if (ret)
> > > + goto clk_err;
> >
> > Please name the goto labels of their purpose. Like err_phy_exit.
>
> OK
>
> >
> > > +
> > > + ret = dw_pcie_setup_rc(pp);
> > > + if (ret)
> > > + goto pcie_err;
> >
> > This should be, 'err_disable_clk'.
> >
> > > +
> > > + if (stm32_pcie->link_is_up) {
> >
> > Why do you need this check? You cannot start the link in the absence of an
> > endpoint?
> >
>
> It is an optimization to avoid unnecessary "dw_pcie_wait_for_link" if no
> device is present during suspend
>

In that case you'll not trigger LTSSM if there was no endpoint connected before
suspend. What if users connect an endpoint after resume?

- Mani

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