Re: [PATCH v2 03/10] PCI/DOE: Provide synchronous API and use it internally

[Ira Weiny <ira.weiny@intel.com>]

Jonathan Cameron wrote:
> On Mon, 23 Jan 2023 11:13:00 +0100
> Lukas Wunner <lukas@wunner.de> wrote:
> 
> > The DOE API only allows asynchronous exchanges and forces callers to
> > provide a completion callback.  Yet all existing callers only perform
> > synchronous exchanges.  Upcoming commits for CMA (Component Measurement
> > and Authentication, PCIe r6.0 sec 6.31) likewise require only
> > synchronous DOE exchanges.
> > 
> > Provide a synchronous pci_doe() API call which builds on the internal
> > asynchronous machinery.
> > 
> > Convert the internal pci_doe_discovery() to the new call.
> > 
> > The new API allows submission of const-declared requests, necessitating
> > the addition of a const qualifier in struct pci_doe_task.
> > 
> > Tested-by: Ira Weiny <ira.weiny@intel.com>
> > Signed-off-by: Lukas Wunner <lukas@wunner.de>
> > Cc: Dan Williams <dan.j.williams@intel.com>
> > Cc: Jonathan Cameron <Jonathan.Cameron@Huawei.com>
> 
> Pushing the struct down is fine by me, though I'll note we had it
> pretty much like this in one of the earlier versions and got a
> request to use a struct instead to wrap up all the parameters.

I had the same thought but decided not to pick at that old wound...  ;-)

> 
> Let's see if experience convinces people this is the right
> approach this time :) It is perhaps easier to argue
> now the completion is moved down as well as we'd end up with
> a messy case of some elements of the structure being set in the
> caller and others inside where it is called (or some messy
> wrapper structures).  Been a while, but I don't think we had
> such a strong argument in favour of this approach back then.

I think this makes a lot of sense and is clean enough.  I don't think the
number of parameters is outrageous.

Ira

> 
> The const changes makes sense independent of the rest.
> 
> Reviewed-by: Jonathan Cameron <Jonathan.Cameron@huawei.com>
> 
> 
> > ---
> >  drivers/pci/doe.c       | 65 +++++++++++++++++++++++++++++++----------
> >  include/linux/pci-doe.h |  6 +++-
> >  2 files changed, 55 insertions(+), 16 deletions(-)
> > 
> > diff --git a/drivers/pci/doe.c b/drivers/pci/doe.c
> > index 7451b5732044..dce6af2ab574 100644
> > --- a/drivers/pci/doe.c
> > +++ b/drivers/pci/doe.c
> > @@ -319,26 +319,15 @@ static int pci_doe_discovery(struct pci_doe_mb *doe_mb, u8 *index, u16 *vid,
> >  	u32 request_pl = FIELD_PREP(PCI_DOE_DATA_OBJECT_DISC_REQ_3_INDEX,
> >  				    *index);
> >  	u32 response_pl;
> > -	DECLARE_COMPLETION_ONSTACK(c);
> > -	struct pci_doe_task task = {
> > -		.prot.vid = PCI_VENDOR_ID_PCI_SIG,
> > -		.prot.type = PCI_DOE_PROTOCOL_DISCOVERY,
> > -		.request_pl = &request_pl,
> > -		.request_pl_sz = sizeof(request_pl),
> > -		.response_pl = &response_pl,
> > -		.response_pl_sz = sizeof(response_pl),
> > -		.complete = pci_doe_task_complete,
> > -		.private = &c,
> > -	};
> >  	int rc;
> >  
> > -	rc = pci_doe_submit_task(doe_mb, &task);
> > +	rc = pci_doe(doe_mb, PCI_VENDOR_ID_PCI_SIG, PCI_DOE_PROTOCOL_DISCOVERY,
> > +		     &request_pl, sizeof(request_pl),
> > +		     &response_pl, sizeof(response_pl));
> >  	if (rc < 0)
> >  		return rc;
> >  
> > -	wait_for_completion(&c);
> > -
> > -	if (task.rv != sizeof(response_pl))
> > +	if (rc != sizeof(response_pl))
> >  		return -EIO;
> >  
> >  	*vid = FIELD_GET(PCI_DOE_DATA_OBJECT_DISC_RSP_3_VID, response_pl);
> > @@ -549,3 +538,49 @@ int pci_doe_submit_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task)
> >  	return 0;
> >  }
> >  EXPORT_SYMBOL_GPL(pci_doe_submit_task);
> > +
> > +/**
> > + * pci_doe() - Perform Data Object Exchange
> > + *
> > + * @doe_mb: DOE Mailbox
> > + * @vendor: Vendor ID
> > + * @type: Data Object Type
> > + * @request: Request payload
> > + * @request_sz: Size of request payload (bytes)
> > + * @response: Response payload
> > + * @response_sz: Size of response payload (bytes)
> > + *
> > + * Submit @request to @doe_mb and store the @response.
> > + * The DOE exchange is performed synchronously and may therefore sleep.
> > + *
> > + * RETURNS: Length of received response or negative errno.
> > + * Received data in excess of @response_sz is discarded.
> > + * The length may be smaller than @response_sz and the caller
> > + * is responsible for checking that.
> > + */
> > +int pci_doe(struct pci_doe_mb *doe_mb, u16 vendor, u8 type,
> > +	    const void *request, size_t request_sz,
> > +	    void *response, size_t response_sz)
> > +{
> > +	DECLARE_COMPLETION_ONSTACK(c);
> > +	struct pci_doe_task task = {
> > +		.prot.vid = vendor,
> > +		.prot.type = type,
> > +		.request_pl = request,
> > +		.request_pl_sz = request_sz,
> > +		.response_pl = response,
> > +		.response_pl_sz = response_sz,
> > +		.complete = pci_doe_task_complete,
> > +		.private = &c,
> > +	};
> > +	int rc;
> > +
> > +	rc = pci_doe_submit_task(doe_mb, &task);
> > +	if (rc)
> > +		return rc;
> > +
> > +	wait_for_completion(&c);
> > +
> > +	return task.rv;
> > +}
> > +EXPORT_SYMBOL_GPL(pci_doe);
> > diff --git a/include/linux/pci-doe.h b/include/linux/pci-doe.h
> > index ed9b4df792b8..1608e1536284 100644
> > --- a/include/linux/pci-doe.h
> > +++ b/include/linux/pci-doe.h
> > @@ -45,7 +45,7 @@ struct pci_doe_mb;
> >   */
> >  struct pci_doe_task {
> >  	struct pci_doe_protocol prot;
> > -	u32 *request_pl;
> > +	const u32 *request_pl;
> >  	size_t request_pl_sz;
> >  	u32 *response_pl;
> >  	size_t response_pl_sz;
> > @@ -74,4 +74,8 @@ struct pci_doe_mb *pcim_doe_create_mb(struct pci_dev *pdev, u16 cap_offset);
> >  bool pci_doe_supports_prot(struct pci_doe_mb *doe_mb, u16 vid, u8 type);
> >  int pci_doe_submit_task(struct pci_doe_mb *doe_mb, struct pci_doe_task *task);
> >  
> > +int pci_doe(struct pci_doe_mb *doe_mb, u16 vendor, u8 type,
> > +	    const void *request, size_t request_sz,
> > +	    void *response, size_t response_sz);
> > +
> >  #endif
>