[Skiboot] [PATCH-RESEND] phb4: Reset FIR/NFIR registers before PHB4 probe

[Benjamin Herrenschmidt]

On Mon, 2018-04-02 at 16:12 +0530, Vaibhav Jain wrote:
> The function phb4_probe_stack() resets "ETU Reset Register" to
> unfreeze the PHB before it performs mmio access on the PHB. However in
> case the FIR/NFIR registers are set while entering this function,
> the reset of "ETU Reset Register" wont unfreeze the PHB and it will
> remain fenced. This leads to failure during initial CRESET of the PHB
> as mmio access is still not enabled and an error message of the form
> below is logged:
> 
>  PHB#0000[0:0]: Initializing PHB4...
>  PHB#0000[0:0]: Default system config: 0xffffffffffffffff
>  PHB#0000[0:0]: New system config    : 0xffffffffffffffff
>  PHB#0000[0:0]: Initial PHB CRESET is 0xffffffffffffffff
>  PHB#0000[0:0]: Waiting for DLP PG reset to complete...
>  <snip>
>  PHB#0000[0:0]: Timeout waiting for DLP PG reset !
>  PHB#0000[0:0]: Initialization failed
> 
> This is especially seen happening during the MPIPL flow where SBE
> would quiesces and fence the PHB so that it doesn't stomp on the main
> memory. However when skiboot enters phb4_probe_stack() after MPIPL,
> the FIR/NFIR registers are set forcing PHB to re-enter fence after ETU
> reset is done.
> 
> So to fix this issue the patch introduces new xscom writes to
> phb4_probe_stack() to reset the FIR/NFIR registers before performing
> ETU reset to enable mmio access to the PHB.
> 
> Signed-off-by: Vaibhav Jain <vaibhav at linux.vnet.ibm.com>
> Tested-by: Vasant Hegde <hegdevasant at linux.vnet.ibm.com>

Acked-by: Benjamin Herrenschmidt <benh at kernel.crashing.org>

> ---
> Change-log:
> 
> Resend -> Replaced xscom_read to FIR/NFIR registers with xscom_write.
> ---
>  hw/phb4.c | 9 +++++++++
>  1 file changed, 9 insertions(+)
> 
> diff --git a/hw/phb4.c b/hw/phb4.c
> index e45be01f..c5a33a0f 100644
> --- a/hw/phb4.c
> +++ b/hw/phb4.c
> @@ -5315,6 +5315,15 @@ static void phb4_probe_stack(struct dt_node *stk_node, uint32_t pec_index,
>  		return;
>  	}
>  
> +	/* Clear errors in PFIR and NFIR */
> +	xscom_read(gcid, pci_stack + XPEC_PCI_STK_PCI_FIR, &val);
> +	prlog_once(PR_DEBUG, "PFIR: %llx\n", val);
> +	xscom_write(gcid, pci_stack + XPEC_PCI_STK_PCI_FIR, 0);
> +
> +	xscom_read(gcid, nest_stack + XPEC_NEST_STK_PCI_NFIR, &val);
> +	prlog_once(PR_DEBUG, "NFIR: %llx\n", val);
> +	xscom_write(gcid, nest_stack + XPEC_NEST_STK_PCI_NFIR, 0);
> +
>  	/* Check ETU reset */
>  	xscom_read(gcid, pci_stack + XPEC_PCI_STK_ETU_RESET, &val);
>  	prlog_once(PR_DEBUG, "ETU reset: %llx\n", val);