[Skiboot] [PATCH 3/5] nvlink: Add fence mode emulation for NPUs

[Alistair Popple]

On Thu, 7 Jan 2016 14:36:30 Russell Currey wrote:
> As NPUs are emulated PCI devices, they do not get physically fenced as real
> PCI devices to.  As such, when the device is in a state that it should be

PCI devices *do* :)

Stewart can probably fix that up when he pulls I guess...

> 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>
> ---
>  hw/npu.c      | 7 +++++++
>  include/npu.h | 1 +
>  2 files changed, 8 insertions(+)
> 
> diff --git a/hw/npu.c b/hw/npu.c
> index 3a06c04..9440f17 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)
> @@ -1680,6 +1684,9 @@ static void npu_create_phb(struct dt_node *dn)
>  	p->xscom_base = dt_prop_get_u32(dn, "ibm,xscom-base");
>  	p->total_devices = links;
>  
> +	/* XXX: is there any chance we're *already* fenced? */

It's possible the HW is but this patch is purely for the fence 
emulation/injection. We can fix this up once we've wired up the actual 
hardware to detect fence conditions.

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

> +	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;
>  };
>