[Skiboot] [PATCH V2 2/4] nvlink: Add fence mode emulation for NPUs

[Alistair Popple]

I like the clarification, thanks.

Acked-By: Alistair Popple <alistair at popple.id.au>

On Mon, 18 Jan 2016 16:59:40 Russell Currey wrote:
> As NPUs are emulated PCI devices, they do not get physically fenced as real
> PCI devices do.  As such, when the device is in a state that it should be
> fenced, we need to emulate this behaviour by returning all 1s in config
> space reads.
> 
> This will be utilised by error injection in subsequent patches.
> 
> Signed-off-by: Russell Currey <ruscur at russell.cc>
> ---
> V2: Clarify fence comment and move freeze status change to this patch
> ---
>  hw/npu.c      | 15 +++++++++++++--
>  include/npu.h |  1 +
>  2 files changed, 14 insertions(+), 2 deletions(-)
> 
> diff --git a/hw/npu.c b/hw/npu.c
> index 3a06c04..3c2c0b8 100644
> --- a/hw/npu.c
> +++ b/hw/npu.c
> @@ -390,6 +390,10 @@ static int64_t _npu_dev_cfg_read(struct phb *phb, uint32_t bdfn,
>  	/* Data returned upon errors */
>  	*data = 0xffffffff;
>  
> +	/* If fenced, we want to return all 1s, so we're done. */
> +	if (p->fenced)
> +		return OPAL_SUCCESS;
> +
>  	/* Retrieve NPU device */
>  	dev = npu_dev_cfg_check(p, bdfn, offset, size);
>  	if (!dev)
> @@ -996,7 +1000,7 @@ static int64_t npu_freset(struct phb *phb __unused)
>  	return OPAL_SUCCESS;
>  }
>  
> -static int64_t npu_freeze_status(struct phb *phb __unused,
> +static int64_t npu_freeze_status(struct phb *phb,
>  				     uint64_t pe_number __unused,
>  				     uint8_t *freeze_state,
>  				     uint16_t *pci_error_type __unused,
> @@ -1008,7 +1012,11 @@ static int64_t npu_freeze_status(struct phb *phb __unused,
>  	 * introduce another PHB callback to translate it. For now,
>  	 * it keeps the skiboot PCI enumeration going.
>  	 */
> -	*freeze_state = OPAL_EEH_STOPPED_NOT_FROZEN;
> +	struct npu *p = phb_to_npu(phb);
> +	if (p->fenced)
> +		*freeze_state = OPAL_EEH_STOPPED_MMIO_DMA_FREEZE;
> +	else
> +		*freeze_state = OPAL_EEH_STOPPED_NOT_FROZEN;
>  	return OPAL_SUCCESS;
>  }
>  
> @@ -1680,6 +1688,9 @@ static void npu_create_phb(struct dt_node *dn)
>  	p->xscom_base = dt_prop_get_u32(dn, "ibm,xscom-base");
>  	p->total_devices = links;
>  
> +	/* TODO: When hardware fences are implemented, detect them here */
> +	p->fenced = false;
> +
>  	/* This is the AT base */
>  	p->at_xscom = p->xscom_base + NPU_AT_SCOM_OFFSET;
>  	p->at_regs = (void *)dt_get_address(dn, 0, NULL);
> diff --git a/include/npu.h b/include/npu.h
> index 795b704..5d5135b 100644
> --- a/include/npu.h
> +++ b/include/npu.h
> @@ -167,6 +167,7 @@ struct npu {
>  	uint64_t		tve_cache[NPU_NUM_OF_PES];
>  
>  	bool			tx_zcal_complete[2];
> +	bool			fenced;
>  
>  	struct phb		phb;
>  };
>