Re: [PATCH v2 2/6] PCI: cadence: Add quirk flag to set minimum delay in LTSSM Detect.Quiet state

Lorenzo Pieralisi
2021-08-03T10:09:06Z

On Tue, Aug 03, 2021 at 01:19:28PM +0530, Kishon Vijay Abraham I wrote:
> From: Nadeem Athani <nadeem@cadence.com>
>
> PCIe fails to link up if SERDES lanes not used by PCIe are assigned to
> another protocol. For example, link training fails if lanes 2 and 3 are
> assigned to another protocol while lanes 0 and 1 are used for PCIe to
> form a two lane link. This failure is due to an incorrect tie-off on an
> internal status signal indicating electrical idle.
>
> Status signals going from SERDES to PCIe Controller are tied-off when a
> lane is not assigned to PCIe. Signal indicating electrical idle is
> incorrectly tied-off to a state that indicates non-idle. As a result,
> PCIe sees unused lanes to be out of electrical idle and this causes
> LTSSM to exit Detect.Quiet state without waiting for 12ms timeout to
> occur. If a receiver is not detected on the first receiver detection
> attempt in Detect.Active state, LTSSM goes back to Detect.Quiet and
> again moves forward to Detect.Active state without waiting for 12ms as
> required by PCIe base specification. Since wait time in Detect.Quiet is
> skipped, multiple receiver detect operations are performed back-to-back
> without allowing time for capacitance on the transmit lines to
> discharge. This causes subsequent receiver detection to always fail even
> if a receiver gets connected eventually.
>
> Add a quirk flag "quirk_detect_quiet_flag" to program the minimum
> time the LTSSM should wait on entering Detect.Quiet state here.
> This has to be set for J7200 as it has an incorrect tie-off on unused
> lanes.
>
> Signed-off-by: Nadeem Athani <nadeem@cadence.com>
> Signed-off-by: Kishon Vijay Abraham I <kishon@ti.com>
> ---
> .../pci/controller/cadence/pcie-cadence-ep.c | 4 ++++
> .../pci/controller/cadence/pcie-cadence-host.c | 3 +++
> drivers/pci/controller/cadence/pcie-cadence.c | 17 +++++++++++++++++
> drivers/pci/controller/cadence/pcie-cadence.h | 15 +++++++++++++++
> 4 files changed, 39 insertions(+)
>
> diff --git a/drivers/pci/controller/cadence/pcie-cadence-ep.c b/drivers/pci/controller/cadence/pcie-cadence-ep.c
> index 791915054ff4..e05c157afef0 100644
> --- a/drivers/pci/controller/cadence/pcie-cadence-ep.c
> +++ b/drivers/pci/controller/cadence/pcie-cadence-ep.c
> @@ -804,6 +804,10 @@ int cdns_pcie_ep_setup(struct cdns_pcie_ep *ep)
> ep->irq_pci_addr = CDNS_PCIE_EP_IRQ_PCI_ADDR_NONE;
> /* Reserve region 0 for IRQs */
> set_bit(0, &ep->ob_region_map);
> +
> + if (ep->quirk_detect_quiet_flag)
> + cdns_pcie_detect_quiet_min_delay_set(&ep->pcie);
> +
> spin_lock_init(&ep->lock);
>
> return 0;
> diff --git a/drivers/pci/controller/cadence/pcie-cadence-host.c b/drivers/pci/controller/cadence/pcie-cadence-host.c
> index ae1c55503513..fb96d37a135c 100644
> --- a/drivers/pci/controller/cadence/pcie-cadence-host.c
> +++ b/drivers/pci/controller/cadence/pcie-cadence-host.c
> @@ -498,6 +498,9 @@ int cdns_pcie_host_setup(struct cdns_pcie_rc *rc)
> return PTR_ERR(rc->cfg_base);
> rc->cfg_res = res;
>
> + if (rc->quirk_detect_quiet_flag)
> + cdns_pcie_detect_quiet_min_delay_set(&rc->pcie);
> +
> ret = cdns_pcie_start_link(pcie);
> if (ret) {
> dev_err(dev, "Failed to start link\n");
> diff --git a/drivers/pci/controller/cadence/pcie-cadence.c b/drivers/pci/controller/cadence/pcie-cadence.c
> index 3c3646502d05..65b6c8bed0d4 100644
> --- a/drivers/pci/controller/cadence/pcie-cadence.c
> +++ b/drivers/pci/controller/cadence/pcie-cadence.c
> @@ -7,6 +7,23 @@
>
> #include "pcie-cadence.h"
>
> +void cdns_pcie_detect_quiet_min_delay_set(struct cdns_pcie *pcie)
> +{
> + u32 delay = 0x3;
> + u32 ltssm_control_cap;
> +
> + /*
> + * Set the LTSSM Detect Quiet state min. delay to 2ms.
> + */
> +

Nit: empty line not needed

> + ltssm_control_cap = cdns_pcie_readl(pcie, CDNS_PCIE_LTSSM_CONTROL_CAP);
> + ltssm_control_cap = ((ltssm_control_cap &
> + ~CDNS_PCIE_DETECT_QUIET_MIN_DELAY_MASK) |
> + CDNS_PCIE_DETECT_QUIET_MIN_DELAY(delay));
> +
> + cdns_pcie_writel(pcie, CDNS_PCIE_LTSSM_CONTROL_CAP, ltssm_control_cap);
> +}
> +
> void cdns_pcie_set_outbound_region(struct cdns_pcie *pcie, u8 busnr, u8 fn,
> u32 r, bool is_io,
> u64 cpu_addr, u64 pci_addr, size_t size)
> diff --git a/drivers/pci/controller/cadence/pcie-cadence.h b/drivers/pci/controller/cadence/pcie-cadence.h
> index a978a2eeedad..cda430d0f6e4 100644
> --- a/drivers/pci/controller/cadence/pcie-cadence.h
> +++ b/drivers/pci/controller/cadence/pcie-cadence.h
> @@ -194,6 +194,14 @@
> /* AXI link down register */
> #define CDNS_PCIE_AT_LINKDOWN (CDNS_PCIE_AT_BASE + 0x0824)
>
> +/* LTSSM Capabilities register */
> +#define CDNS_PCIE_LTSSM_CONTROL_CAP (CDNS_PCIE_LM_BASE + 0x0054)
> +#define CDNS_PCIE_DETECT_QUIET_MIN_DELAY_MASK GENMASK(2, 1)
> +#define CDNS_PCIE_DETECT_QUIET_MIN_DELAY_SHIFT 1
> +#define CDNS_PCIE_DETECT_QUIET_MIN_DELAY(delay) \
> + (((delay) << CDNS_PCIE_DETECT_QUIET_MIN_DELAY_SHIFT) & \
> + CDNS_PCIE_DETECT_QUIET_MIN_DELAY_MASK)
> +
> enum cdns_pcie_rp_bar {
> RP_BAR_UNDEFINED = -1,
> RP_BAR0,
> @@ -300,6 +308,7 @@ struct cdns_pcie {
> * @avail_ib_bar: Satus of RP_BAR0, RP_BAR1 and RP_NO_BAR if it's free or
> * available
> * @quirk_retrain_flag: Retrain link as quirk for PCIe Gen2
> + * @quirk_detect_quiet_flag: LTSSM Detect Quiet min delay set as quirk
> */
> struct cdns_pcie_rc {
> struct cdns_pcie pcie;
> @@ -309,6 +318,7 @@ struct cdns_pcie_rc {
> u32 device_id;
> bool avail_ib_bar[CDNS_PCIE_RP_MAX_IB];
> unsigned int quirk_retrain_flag:1;
> + unsigned int quirk_detect_quiet_flag:1;
> };
>
> /**
> @@ -341,6 +351,7 @@ struct cdns_pcie_epf {
> * registers fields (RMW) accessible by both remote RC and EP to
> * minimize time between read and write
> * @epf: Structure to hold info about endpoint function
> + * @quirk_detect_quiet_flag: LTSSM Detect Quiet min delay set as quirk
> */
> struct cdns_pcie_ep {
> struct cdns_pcie pcie;
> @@ -355,6 +366,7 @@ struct cdns_pcie_ep {
> /* protect writing to PCI_STATUS while raising legacy interrupts */
> spinlock_t lock;
> struct cdns_pcie_epf *epf;
> + unsigned int quirk_detect_quiet_flag:1;
> };
>
>
> @@ -515,6 +527,9 @@ static inline int cdns_pcie_ep_setup(struct cdns_pcie_ep *ep)
> return 0;
> }
> #endif
> +
> +void cdns_pcie_detect_quiet_min_delay_set(struct cdns_pcie *pcie);
> +
> void cdns_pcie_set_outbound_region(struct cdns_pcie *pcie, u8 busnr, u8 fn,
> u32 r, bool is_io,
> u64 cpu_addr, u64 pci_addr, size_t size);
> --
> 2.17.1
>