Re: [PATCH 3/5] ocxl: Tally up the LPC memory on a link & allow it to be mapped

[Alastair D'Silva]

On Wed, 2019-09-18 at 16:02 +0200, Frederic Barrat wrote:
> 
> Le 17/09/2019 Ã 03:42, Alastair D'Silva a Ãcrit :
> > From: Alastair D'Silva <alastair@xxxxxxxxxxx>
> > 
> > Tally up the LPC memory on an OpenCAPI link & allow it to be mapped
> > 
> > Signed-off-by: Alastair D'Silva <alastair@xxxxxxxxxxx>
> > ---
> >   drivers/misc/ocxl/core.c          |  9 +++++
> >   drivers/misc/ocxl/link.c          | 61
> > +++++++++++++++++++++++++++++++
> >   drivers/misc/ocxl/ocxl_internal.h | 42 +++++++++++++++++++++
> >   3 files changed, 112 insertions(+)
> > 
> > diff --git a/drivers/misc/ocxl/core.c b/drivers/misc/ocxl/core.c
> > index b7a09b21ab36..fdfe4e0a34e1 100644
> > --- a/drivers/misc/ocxl/core.c
> > +++ b/drivers/misc/ocxl/core.c
> > @@ -230,8 +230,17 @@ static int configure_afu(struct ocxl_afu *afu,
> > u8 afu_idx, struct pci_dev *dev)
> >   	if (rc)
> >   		goto err_free_pasid;
> >   
> > +	if (afu->config.lpc_mem_size || afu-
> > >config.special_purpose_mem_size) {
> > +		rc = ocxl_link_add_lpc_mem(afu->fn->link,
> > +			afu->config.lpc_mem_size + afu-
> > >config.special_purpose_mem_size);
> 
> I don't think we should count the special purpose memory, as it's
> not 
> meant to be accessed through the GPU mem BAR, but I'll check.

At least for OpenCAPI 3.0, there is no other in-spec way to access the
memory if it is not mapped by the NPU.

> 
> What happens when unconfiguring the AFU? We should reduce the range
> (see 
> also below). Partial reconfig doesn't seem so far off, so we should
> take 
> it into account.
> 

The mapping is left until the last AFU on the link offlines it's
memory, at which point we clear the mapping from the NPU.

> 
> > +		if (rc)
> > +			goto err_free_mmio;
> > +	}
> > +
> >   	return 0;
> >   
> > +err_free_mmio:
> > +	unmap_mmio_areas(afu);
> >   err_free_pasid:
> >   	reclaim_afu_pasid(afu);
> >   err_free_actag:
> > diff --git a/drivers/misc/ocxl/link.c b/drivers/misc/ocxl/link.c
> > index 58d111afd9f6..2874811a4398 100644
> > --- a/drivers/misc/ocxl/link.c
> > +++ b/drivers/misc/ocxl/link.c
> > @@ -84,6 +84,11 @@ struct ocxl_link {
> >   	int dev;
> >   	atomic_t irq_available;
> >   	struct spa *spa;
> > +	struct mutex lpc_mem_lock;
> > +	u64 lpc_mem_sz; /* Total amount of LPC memory presented on the
> > link */
> > +	u64 lpc_mem;
> > +	int lpc_consumers;
> > +
> >   	void *platform_data;
> >   };
> >   static struct list_head links_list = LIST_HEAD_INIT(links_list);
> > @@ -396,6 +401,8 @@ static int alloc_link(struct pci_dev *dev, int
> > PE_mask, struct ocxl_link **out_l
> >   	if (rc)
> >   		goto err_spa;
> >   
> > +	mutex_init(&link->lpc_mem_lock);
> > +
> >   	/* platform specific hook */
> >   	rc = pnv_ocxl_spa_setup(dev, link->spa->spa_mem, PE_mask,
> >   				&link->platform_data);
> > @@ -711,3 +718,57 @@ void ocxl_link_free_irq(void *link_handle, int
> > hw_irq)
> >   	atomic_inc(&link->irq_available);
> >   }
> >   EXPORT_SYMBOL_GPL(ocxl_link_free_irq);
> > +
> > +int ocxl_link_add_lpc_mem(void *link_handle, u64 size)
> > +{
> > +	struct ocxl_link *link = (struct ocxl_link *) link_handle;
> > +
> > +	u64 orig_size;
> > +	bool good = false;
> > +
> > +	mutex_lock(&link->lpc_mem_lock);
> > +	orig_size = link->lpc_mem_sz;
> > +	link->lpc_mem_sz += size;
> 
> 
> We have a choice to make here:
> 1. either we only support one LPC memory-carrying AFU (and the above
> is 
> overkill)
> 2. or we support multiple AFUs with LPC memory (on the same
> function), 
> but then I think the above is too simple.
> 
>  From the opencapi spec, each AFU can define a chunk of memory with
> a 
> starting address and a size. There's no rule which says they have to
> be 
> contiguous. There's no rule which says it must start at 0. So to
> support 
> multiple AFUs with LPC memory, we should record the current maximum 
> range instead of just the global size. Ultimately, we need to tell
> the 
> NPU the range of permissible addresses. It starts at 0, so we need
> to 
> take into account any intial offset and holes.
> 
> I would go for option 2, to at least be consistent within ocxl and 
> support multiple AFUs. Even though I don't think we'll see FPGA
> images 
> with multiple AFUs with LPC memory any time soon.
> 

Ill rework this to take an offset & size, the NPU will map from the
base address up to the largest offset + size provided across all AFUs
on the link.

> 
> > +	good = orig_size < link->lpc_mem_sz;
> > +	mutex_unlock(&link->lpc_mem_lock);
> > +
> > +	// Check for overflow
> > +	return (good) ? 0 : -EINVAL;
> > +}
> > +EXPORT_SYMBOL_GPL(ocxl_link_add_lpc_mem);
> 
> Do the symbol really need to be exported? IIUC, the next patch
> defines a 
> higher level ocxl_afu_map_lpc_mem() which is meant to be called by a 
> calling driver.
> 

No, I'll remove it.

> 
> > +
> > +u64 ocxl_link_lpc_map(void *link_handle, struct pci_dev *pdev)
> > +{
> > +	struct ocxl_link *link = (struct ocxl_link *) link_handle;
> > +
> > +	mutex_lock(&link->lpc_mem_lock);
> > +	if (link->lpc_mem) {
> > +		u64 lpc_mem = link->lpc_mem;
> > +
> > +		link->lpc_consumers++;
> > +		mutex_unlock(&link->lpc_mem_lock);
> > +		return lpc_mem;
> > +	}
> > +
> > +	link->lpc_mem = pnv_ocxl_platform_lpc_setup(pdev, link-
> > >lpc_mem_sz);
> > +	if (link->lpc_mem)
> > +		link->lpc_consumers++;
> > +	mutex_unlock(&link->lpc_mem_lock);
> > +
> > +	return link->lpc_mem;
> 
> Should be cached in a temp variable, like on the fast path,
> otherwise 
> it's accessed with no lock.

Good spotting, thanks.

> 
> > +}
> > +
> > +void ocxl_link_lpc_release(void *link_handle, struct pci_dev
> > *pdev)
> > +{
> > +	struct ocxl_link *link = (struct ocxl_link *) link_handle;
> > +
> > +	mutex_lock(&link->lpc_mem_lock);
> > +	link->lpc_consumers--;
> > +	if (link->lpc_consumers == 0) {
> > +		pnv_ocxl_platform_lpc_release(pdev);
> > +		link->lpc_mem = 0;
> > +	}
> > +
> > +	mutex_unlock(&link->lpc_mem_lock);
> > +}
> > diff --git a/drivers/misc/ocxl/ocxl_internal.h
> > b/drivers/misc/ocxl/ocxl_internal.h
> > index 97415afd79f3..db2647a90fc8 100644
> > --- a/drivers/misc/ocxl/ocxl_internal.h
> > +++ b/drivers/misc/ocxl/ocxl_internal.h
> > @@ -141,4 +141,46 @@ int ocxl_irq_offset_to_id(struct ocxl_context
> > *ctx, u64 offset);
> >   u64 ocxl_irq_id_to_offset(struct ocxl_context *ctx, int irq_id);
> >   void ocxl_afu_irq_free_all(struct ocxl_context *ctx);
> >   
> > +/**
> > + * Increment the amount of memory required by an OpenCAPI link
> > + *
> > + * link_handle: The OpenCAPI link handle
> > + * size: The amount of memory to increment by
> > + *
> > + * Return 0 on success, negative on overflow
> > + */
> > +extern int ocxl_link_add_lpc_mem(void *link_handle, u64 size);
> 
> We've removed all the 'extern' in a previous patch.

Thanks, I spotted this too (after I posted it).

> > +
> > +/**
> > + * Get the amount of memory required by an OpenCAPI link
> > + *
> > + * link_handle: The OpenCAPI link handle
> > + *
> > + * Return the amount of memory required by the link, this value is
> > undefined if
> > + * ocxl_link_add_lpc_mem failed.
> > + */
> > +extern u64 ocxl_link_get_lpc_mem_sz(void *link_handle);
> 
> I don't see that one defined anywhere.
> 

Whoops, I'll remove it.

>    Fred
> 
> 
> > +
> > +/**
> > + * Map the LPC memory for an OpenCAPI device
> > + *
> > + * Since LPC memory belongs to a link, the whole LPC memory
> > available
> > + * on the link bust be mapped in order to make it accessible to a
> > device.
> > + *
> > + * @link_handle: The OpenCAPI link handle
> > + * @pdev: A device that is on the link
> > + */
> > +u64 ocxl_link_lpc_map(void *link_handle, struct pci_dev *pdev);
> > +
> > +/**
> > + * Release the LPC memory device for an OpenCAPI device
> > + *
> > + * Releases LPC memory on an OpenCAPI link for a device. If this
> > is the
> > + * last device on the link to release the memory, unmap it from
> > the link.
> > + *
> > + * @link_handle: The OpenCAPI link handle
> > + * @pdev: A device that is on the link
> > + */
> > +void ocxl_link_lpc_release(void *link_handle, struct pci_dev
> > *pdev);
> > +
> >   #endif /* _OCXL_INTERNAL_H_ */
> > 
-- 
Alastair D'Silva
Open Source Developer
Linux Technology Centre, IBM Australia
mob: 0423 762 819