Re: [PATCH 10/11] PCI: qcom-ep: Rework {start/stop}_link() callbacks implementation

Manivannan Sadhasivam
2024-03-26T08:33:46Z

On Fri, Mar 22, 2024 at 05:10:54PM +0100, Niklas Cassel wrote:
> On Thu, Mar 14, 2024 at 08:53:49PM +0530, Manivannan Sadhasivam wrote:
> > DWC specific start_link() and stop_link() callbacks are supposed to start
> > and stop the link training of the PCIe bus. But the current implementation
> > of this driver enables/disables the PERST# IRQ.
> >
> > Even though this is not causing any issues, this creates inconsistency
> > among the controller drivers. So for the sake of consistency, let's just
> > start/stop the link training in these callbacks.
> >
> > Also, PERST# IRQ is now enabled from the start itself, thus allowing the
> > controller driver to initialize the registers when PERST# gets deasserted
> > without waiting for the user intervention though configfs.
> >
> > Signed-off-by: Manivannan Sadhasivam <manivannan.sadhasivam@linaro.org>
> > ---
>
> Nice change:
> Reviewed-by: Niklas Cassel <cassel@kernel.org>
>
> If you dump LTSSM after a PERST assert + deassert,
> using e.g. dw_pcie_readl_dbi(pci, PCIE_PORT_DEBUG1);
> to dump the debug registers (see dw_pcie_link_up())
> do you see that PCIE_PORT_DEBUG1_LINK_IN_TRAINING is set?
>
> I was thinking that perhaps there was a thought behind
> this original design, that you had to explicitly set
> LTSSM_EN after a fundamental core reset, because it
> would get cleared?
>

Well, you are right. I was hoping to get an answer from Kishon/Vidya, but you
throwed the light. I will drop these 2 patches.

Thanks!

- Mani

> (It it is implemented like signals and not registers,
> then this change should be fine.)
>
>
> Kind regards,
> Niklas
>
>
> > drivers/pci/controller/dwc/pcie-qcom-ep.c | 21 +++++++++++++--------
> > 1 file changed, 13 insertions(+), 8 deletions(-)
> >
> > diff --git a/drivers/pci/controller/dwc/pcie-qcom-ep.c b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> > index 811f250e967a..653e4ace0a07 100644
> > --- a/drivers/pci/controller/dwc/pcie-qcom-ep.c
> > +++ b/drivers/pci/controller/dwc/pcie-qcom-ep.c
> > @@ -122,6 +122,9 @@
> > /* PARF_CFG_BITS register fields */
> > #define PARF_CFG_BITS_REQ_EXIT_L1SS_MSI_LTR_EN BIT(1)
> >
> > +/* PARF_LTSSM register fields */
> > +#define LTSSM_EN BIT(8)
> > +
> > /* ELBI registers */
> > #define ELBI_SYS_STTS 0x08
> > #define ELBI_CS2_ENABLE 0xa4
> > @@ -250,8 +253,12 @@ static int qcom_pcie_dw_link_up(struct dw_pcie *pci)
> > static int qcom_pcie_dw_start_link(struct dw_pcie *pci)
> > {
> > struct qcom_pcie_ep *pcie_ep = to_pcie_ep(pci);
> > + u32 val;
> >
> > - enable_irq(pcie_ep->perst_irq);
> > + /* Enable LTSSM */
> > + val = readl_relaxed(pcie_ep->parf + PARF_LTSSM);
> > + val |= LTSSM_EN;
> > + writel_relaxed(val, pcie_ep->parf + PARF_LTSSM);
> >
> > return 0;
> > }
> > @@ -259,8 +266,12 @@ static int qcom_pcie_dw_start_link(struct dw_pcie *pci)
> > static void qcom_pcie_dw_stop_link(struct dw_pcie *pci)
> > {
> > struct qcom_pcie_ep *pcie_ep = to_pcie_ep(pci);
> > + u32 val;
> >
> > - disable_irq(pcie_ep->perst_irq);
> > + /* Disable LTSSM */
> > + val = readl_relaxed(pcie_ep->parf + PARF_LTSSM);
> > + val &= ~LTSSM_EN;
> > + writel_relaxed(val, pcie_ep->parf + PARF_LTSSM);
> > }
> >
> > static void qcom_pcie_dw_write_dbi2(struct dw_pcie *pci, void __iomem *base,
> > @@ -484,11 +495,6 @@ static int qcom_pcie_perst_deassert(struct dw_pcie *pci)
> >
> > dw_pcie_ep_init_notify(&pcie_ep->pci.ep);
> >
> > - /* Enable LTSSM */
> > - val = readl_relaxed(pcie_ep->parf + PARF_LTSSM);
> > - val |= BIT(8);
> > - writel_relaxed(val, pcie_ep->parf + PARF_LTSSM);
> > -
> > return 0;
> >
> > err_disable_resources:
> > @@ -707,7 +713,6 @@ static int qcom_pcie_ep_enable_irq_resources(struct platform_device *pdev,
> > }
> >
> > pcie_ep->perst_irq = gpiod_to_irq(pcie_ep->reset);
> > - irq_set_status_flags(pcie_ep->perst_irq, IRQ_NOAUTOEN);
> > ret = devm_request_threaded_irq(&pdev->dev, pcie_ep->perst_irq, NULL,
> > qcom_pcie_ep_perst_irq_thread,
> > IRQF_TRIGGER_HIGH | IRQF_ONESHOT,
> >
> > --
> > 2.25.1
> >
>

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