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

Niklas Cassel
2024-03-22T16:11:00Z

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?

(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
>