Re: [dpdk-dev] [EXT] Re: [PATCH v3 1/6] drivers: add generic API to find PCI extended cap

[Manish Chopra <manishc@marvell.com>]

> -----Original Message-----
> From: Gaëtan Rivet <grive@u256.net>
> Sent: Monday, July 27, 2020 4:18 AM
> To: Manish Chopra <manishc@marvell.com>
> Cc: jerinjacobk@gmail.com; Jerin Jacob Kollanukkaran <jerinj@marvell.com>;
> ferruh.yigit@intel.com; dev@dpdk.org; Igor Russkikh
> <irusskikh@marvell.com>; Rasesh Mody <rmody@marvell.com>; GR-Everest-
> DPDK-Dev <GR-Everest-DPDK-Dev@marvell.com>; rosen.xu@intel.com;
> tianfei.zhang@intel.com; heinrich.kuhn@netronome.com;
> qiming.yang@intel.com; qi.z.zhang@intel.com
> Subject: Re: [EXT] Re: [PATCH v3 1/6] drivers: add generic API to find PCI
> extended cap
> 
> On 26/07/20 19:47 +0000, Manish Chopra wrote:
> 
> [...]
> 
> > > > diff --git a/lib/librte_pci/rte_pci.h b/lib/librte_pci/rte_pci.h
> > > > index a03235da1..fec51e15a 100644
> > > > --- a/lib/librte_pci/rte_pci.h
> > > > +++ b/lib/librte_pci/rte_pci.h
> > > > @@ -22,6 +22,22 @@ extern "C" {
> > > >  #include <inttypes.h>
> > > >  #include <sys/types.h>
> > > >
> > > > +
> > > > +/*
> > > > + * Conventional PCI and PCI-X Mode 1 devices have 256 bytes of
> > > > + * configuration space.  PCI-X Mode 2 and PCIe devices have 4096
> > > > +bytes of
> > > > + * configuration space.
> > > > + */
> > > > +#define RTE_PCI_CFG_SPACE_SIZE		256
> > > > +#define RTE_PCI_CFG_SPACE_EXP_SIZE	4096
> > > > +
> > > > +/* Extended Capabilities (PCI-X 2.0 and Express) */
> > > > +#define RTE_PCI_EXT_CAP_ID(header)	(header & 0x0000ffff)
> > > > +#define RTE_PCI_EXT_CAP_NEXT(header)	((header >> 20) &
> 0xffc)
> > > > +
> > > > +#define RTE_PCI_EXT_CAP_ID_ERR	0x01	/* Advanced Error
> Reporting
> > > */
> > > > +#define RTE_PCI_EXT_CAP_ID_DSN	0x03	/* Device Serial
> Number */
> > > > +
> > >
> > > I understand that it is more natural to have those defines in the
> > > PCI lib, but I think there is no point in adding them in a separate
> > > lib, while the function using those is in the PCI bus.
> > >
> > > I think the defines should be put right before the
> > > rte_pci_find_next_ext_capability() prototype in
> > > drivers/bus/pci/rte_bus_pci.h.
> >
> > Hello Gaetan,
> >
> > I think these comes in the category of all RTE_PCI_* generic defines
> > (not just use in drivers/bus/pci/), Since caller of the API also need
> > to use it, For example, couple of RTE_PCI_* were added in patch #2
> > used by qede drivers specifically. rte_pci.h sounds more generic than
> rte_bus_pci.h hence I thought it is the suitable place to consolidate them in
> there.
> >
> > Thanks !!
> 
> Reading the additional symbols, particularly about SRIOV capa, I think you
> are right, it's probably better to have it all within rte_pci.h.
> 
> To help developers, it would be better to point in the doc that the capability
> IDs useable as parameter `cap` can be any from RTE_PCI_EXT_CAP_ID_*,
> defined within librte_pci. The dev can then grep it.

Sure, I will add the pointer to librte_pci in the comment section for
rte_pci_find_next_ext_capability()

> 
> One additional thing:
> 
> > > > +#define RTE_PCI_CFG_SPACE_SIZE		256
> > > > +#define RTE_PCI_CFG_SPACE_EXP_SIZE	4096
> > > > +
> > > > +/* Extended Capabilities (PCI-X 2.0 and Express) */
> > > > +#define RTE_PCI_EXT_CAP_ID(header)	(header & 0x0000ffff)
> > > > +#define RTE_PCI_EXT_CAP_NEXT(header)	((header >> 20) &
> 0xffc)
> 
> I think those macros are not useful as part of the public API, they are only
> used to implement rte_pci_find_next_ext_capability(). Can you confirm? If
> this is correct, I think they should be moved to the compilation unit
> implementing rte_pci_find_next_ext_capability().
> 

Hi Gaetan,

Yes Mostly, but there is a similar piece of code left in drivers/raw/ifpga [ifpga_pci_find_ext_capability()] only
which utilizes these symbols as well, which I did not want to be removed/cleaned up must as a part of this
series because that implementation is based on pread() instead of rte_pci_read_config(). I was not sure
if that driver can also directly use rte_pci_find_next_ext_capability() too, I do not have those fpga based devices
to test if at all I were to do that cleanup/removal now in that driver, so I didn't attempt to make such functional
changes in that driver now. [May be this can be cleaned up too later on with proper testing or may be a new API
based on pread() can be added further if those drivers can't use rte_pci_find_next_ext_capability() directly].

Thanks.