[PATCH v2] PCI: imx6: fix boot hang when link already enabled

[Tim Harvey]

On Mon, Jul 21, 2014 at 11:17 AM, Lucas Stach <l.stach at pengutronix.de> wrote:
> This fixes a boot hang observed when the bootloader
> already enabled the PCIe link for it's own use. The
> fundamental problem is that Freescale forgot to wire
> up the core reset, so software doesn't have a sane way
> to get the core into a defined state.
>
> According to the DW PCIe core reference manual configuration
> of the core may only happen when the LTSSM is disabled, so
> this is one of the first things we need to do. Apparently
> this isn't safe to do when the LTSSM is in any other state
> than "detect" as we observe an instant machine hang when
> trying to do so while the link is already up.
>
> As a workaround force LTSSM into detect state right before
> hitting the disable switch.
>
> Reported-by: Fabio Estevam <fabio.estevam at freescale.com>
> Signed-off-by: Lucas Stach <l.stach at pengutronix.de>
> ---
> v2: messed up the first submission by omitting a chunk
>
> Fabios delay workaround worked because of the following
> conditions:
> 1. The driver gets probed and pulls the peripheral reset GPIO
> 2. Peripheral is held in reset, so won't answer any link
> negotiation requests
> 3. The LTSSM times out and falls back into detect state
> after 24ms (that's why a 30ms delay helps)
> 4. After LTSSM entered detect state it's safe to hit the
> disable switch
> ---
>  drivers/pci/host/pci-imx6.c | 11 +++++++++++
>  1 file changed, 11 insertions(+)
>
> diff --git a/drivers/pci/host/pci-imx6.c b/drivers/pci/host/pci-imx6.c
> index a568efaa331c..1c4b4b81fe15 100644
> --- a/drivers/pci/host/pci-imx6.c
> +++ b/drivers/pci/host/pci-imx6.c
> @@ -49,6 +49,9 @@ struct imx6_pcie {
>
>  /* PCIe Port Logic registers (memory-mapped) */
>  #define PL_OFFSET 0x700
> +#define PCIE_PL_PFLR (PL_OFFSET + 0x08)
> +#define PCIE_PL_PFLR_LINK_STATE_MASK           (0x3f << 16)
> +#define PCIE_PL_PFLR_FORCE_LINK                        (1 << 15)
>  #define PCIE_PHY_DEBUG_R0 (PL_OFFSET + 0x28)
>  #define PCIE_PHY_DEBUG_R1 (PL_OFFSET + 0x2c)
>  #define PCIE_PHY_DEBUG_R1_XMLH_LINK_IN_TRAINING        (1 << 29)
> @@ -214,7 +217,15 @@ static int imx6q_pcie_abort_handler(unsigned long addr,
>  static int imx6_pcie_assert_core_reset(struct pcie_port *pp)
>  {
>         struct imx6_pcie *imx6_pcie = to_imx6_pcie(pp);
> +       u32 val;
> +
> +       val = readl(pp->dbi_base + PCIE_PL_PFLR);
> +       val &= ~PCIE_PL_PFLR_LINK_STATE_MASK;
> +       val |= PCIE_PL_PFLR_FORCE_LINK;
> +       writel(val, pp->dbi_base + PCIE_PL_PFLR);
>
> +       regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR12,
> +                       IMX6Q_GPR12_PCIE_CTL_2, 0 << 10);
>         regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1,
>                         IMX6Q_GPR1_PCIE_TEST_PD, 1 << 18);
>         regmap_update_bits(imx6_pcie->iomuxc_gpr, IOMUXC_GPR1,
> --
> 2.0.1
>
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Lucas,

Thank you - this does resolve the hang on all my board configurations
(with and without bridges, external and internal clock-gen).

Acked-by: Tim Harvey <tharvey at gateworks.com>

Tim