[dpdk-dev] [PATCH 09/11] eal: move PCI table macro

[Neil Horman]

On Fri, Jul 08, 2016 at 04:03:40PM +0200, Thomas Monjalon wrote:
> 2016-07-08 09:56, Neil Horman:
> > On Fri, Jul 08, 2016 at 10:49:25AM +0200, David Marchand wrote:
> > > Hello Thomas, Neil,
> > > 
> > > (will be back in a couple of days, thanks Thomas for pointing this thread)
> > > 
> > > 
> > > On Thu, Jul 7, 2016 at 6:25 PM, Thomas Monjalon
> > > <thomas.monjalon at 6wind.com> wrote:
> > > > 2016-07-07 12:11, Neil Horman:
> > > >> On Thu, Jul 07, 2016 at 05:36:28PM +0200, Thomas Monjalon wrote:
> > > >> > Remove include of rte_pci.h in the generic header rte_dev.h
> > > >> > and move the macro DRIVER_REGISTER_PCI_TABLE in rte_pci.h.
> > > > [...]
> > > >>
> > > >> This seems strange to me, in that its odd for the driver information export
> > > >> macros to be spread out in multiple locations.  Specifically it enjoins the use
> > > >> of the DRV_EXP_TAG macro, which helps centralize tag naming.  Perhaps the happy
> > > >> medium is to place all the export macros (includnig PMD_REGISTER_DRIVER) into
> > > >> its own pmd_register.h header?
> > > >
> > > > I don't know.
> > > > David, your opinion?
> > > 
> > > - The suggestion I did offline to Thomas was to move pci stuff in pci headers.
> > > We are trying to move from the "all pci" code in eal to accomodate for
> > > other "buses" / architectures.
> > I get that, but I'm not sure that applies here.  The macro in question is
> > specific to pci busses, and if there is additional bus information to export, it
> > will have its own macro (e.g. DRIVER_REGISTER_USB_TABLE or some such).  While
> > I could see that being an argument for putting each macro in with its own bus
> > type, I think thats the wrong organization here, in that people writing drivers
> > will want to know what export macros are available and will expect to look in a
> > single place for it.
> > 
> > > Having a pci macro in a generic header like rte_dev.h is wrong to me.
> > > Moving this to a new header like pmd_register.h sounds like a new
> > > generic header with pci specific stuff in it.
> > Well, yes, but I see that as no different than rte_ethdev.c or rte_pdump.c.
> > both of those files will need to know about all the different types of busses
> > you support and have to include those corresponding header files (i.e. they will
> > have to include rte_pci.h, rte_usb.h, rte_i2c.h, etc).  This is really no
> > different in my mind. 
> > 
> > > So, I am not sure I follow you Neil.
> > > 
> > > Can you elaborate ?
> > > 
> > I suppose the best way to describe it is that while I understand and support the
> > desire to separate and abstract bus information away from device function, I
> > think theres a pragmatic descision here to prioritize functional domain over
> > header inclusion.  That is to say, I think when people are writing a driver, it
> > will be helpful to have all the export macros in a single location so they know
> > what information they can export, and that includes registration of various bus
> > type identifiers.  So a file like pmd_registration.h that includes rte_pci.h,
> > rte_usb.h, rte_i2c.h, etc is more useful to a developer, than spreading these
> > macros out to those various header files, for the sake of avoiding a potentially
> > unneeded include.
> > 
> > > 
> > > - Why do you want to centralise the tag naming ?
> > > To avoid collisions ?
> > Yes, and to centralize that information.  Since the pmdinfogen tool needs to
> > know what those tag names are as well, its useful to keep them in the same area
> > to maintain co-ordination.  Its also useful because it means we can use one
> > macro to define tag naming convention, instead of having to re-implement or
> > dead-reckon it in multiple files.
> > 
> > > Well, adding those tags should not happen that often and I think we
> > > can maintain this with careful reviews.
> > I don't agree with that.  This discussion is based on the fact that you expect
> > that we will be adding additional bus types in the future correct?  Well, given
> > that we have a pci bus specific export macro, I would expect that to proliferate
> > to every other bus type as well, and so we can expect to at least have a new
> > tag added for every bus that is added, in addition to any other bus agnostic
> > information people wish to export (just off hand, looking at the linux modinfo
> > section, we might expect module author, module version, alias names, licensing
> > infomration, and others to be potential export candidates).  So, depending on
> > how much this is adopted, I think we can potentially expect a great deal of
> > additional tagging to be needed.
> 
> Anyway, this macro do not need rte_pci.h.
> So the minimal patch can be to just remove this include.
> 
Oh my gosh!  I've been an idiot!  you're absolutely right. The macro is just
defining a string to point to the pci_table symbol name, its not typed to the
pci_tbl symbol at all, and so we can just remove the header file.  Somehow I had
it in my head that the macro created a pci specific typed symbol, but it totally
doesn't.  Apologies.

Yes, just removing the include <rte_pci.h> is exactly the right move here.
Neil