Re: [PATCH v1] net/axgbe: use CPUID to identify cpu

[Bruce Richardson <bruce.richardson@intel.com>]

On Fri, Sep 22, 2023 at 11:43:23AM +0200, David Marchand wrote:
> On Fri, Sep 15, 2023 at 4:35 PM Ferruh Yigit <ferruh.yigit@amd.com> wrote:
> >
> > On 9/15/2023 2:02 PM, David Marchand wrote:
> > > On Fri, Sep 15, 2023 at 12:54 PM Ferruh Yigit <ferruh.yigit@amd.com> wrote:
> > >>
> > >> On 8/31/2023 1:31 PM, Selwin Sebastian wrote:
> > >>> Using root complex to identify cpu will not work for vm passthrough.
> > >>> CPUID is used to get family and modelid to identify cpu
> > >>>
> > >>> Fixes: b0db927b5eba ("net/axgbe: use PCI root complex device to distinguish device")
> > >>> Cc: stable@dpdk.org
> > >>>
> > >>> Signed-off-by: Selwin Sebastian <selwin.sebastian@amd.com>
> > >>> ---
> > >>>  drivers/net/axgbe/axgbe_ethdev.c | 102 ++++++++++++++++++-------------
> > >>>  1 file changed, 59 insertions(+), 43 deletions(-)
> > >>>
> > >>> diff --git a/drivers/net/axgbe/axgbe_ethdev.c b/drivers/net/axgbe/axgbe_ethdev.c
> > >>> index 48714eebe6..59f5d713d0 100644
> > >>> --- a/drivers/net/axgbe/axgbe_ethdev.c
> > >>> +++ b/drivers/net/axgbe/axgbe_ethdev.c
> > >>> @@ -12,6 +12,8 @@
> > >>>
> > >>>  #include "eal_filesystem.h"
> > >>>
> > >>> +#include <cpuid.h>
> > >>> +
> > >>>
> > >>
> > >> This patch cause build errors for some non x86 architecture, because of
> > >> 'cpuid.h'.
> > >>
> > >> There is already a 'rte_cpuid.h' file that includes 'cpuid.h' and it is
> > >> x86 only file.
> > >>
> > >> @Selwin, does it makes sense to implement the feature you are trying to
> > >> get in eal/x86 level and use that API in the driver?
> > >
> > > This driver was expected to compile on all arches.
> > > The meson.build seems to show an intention of compiling/working on non
> > > x86 arch...
> > >
> > > On the other hand (and if I understand correctly the runtime check),
> > > it was never expected to work with anything but a AMD PCI root
> > > complex.
> > >
> > >
> > >>
> > >>
> > >> For those eal/x86 APIs, they will be missing in other architectures,
> > >>
> > >> @David which one is better, to implement APIs for other architectures
> > >> but those just return error, or restrict driver build to x86?
> > >
> > > We gain compilation coverage, but if the vendor itself refuses runtime
> > > on anything but its platform... I don't think we should bother with
> > > this.
> > > Did I miss something?
> > >
> >
> > It is embedded device, so it will only run on x86.
> >
> > Current meson config doesn't restrict it to x86 (existing x86 check is
> > only for vectorization code), but we can restrict if we want to.
> >
> >
> > One option is to restrict driver to x86 arch, and have the local
> > '__cpuid()',
> >
> > other option is move __cpuid() support to eal x86 specific area, so that
> > other components also can benefit from it as well as the driver, similar
> > to the getting CPU flags code, cpuid() is to get some information from
> > CPU, so it is a generic thing, not specific to driver.
> >
> >
> > I think second option is better, but that requires managing this for
> > other archs, my question was related to it.
> 
> Ok, this patch wants to make sure the CPU vendor is AMD and adjust its
> internal configuration based on this AMD processor family.
> And as you mentionned, there is a (ugly asm) piece of code too in mlx5
> that required identifying a Intel processor family.
> 
> I am unclear whether defining a cross arch API for identifying cpu
> model details is doable but I suppose it won't be a quick thing to
> define.
> I came up with a rather simple API, posted it and Cc'd other arch maintainers.
> https://patchwork.dpdk.org/project/dpdk/list/?series=29605&state=%2A&archive=both
> 
> Comments welcome (but not too many, please ;-)).
> 
For this particular change, it seem the only issue with the non-x86 builds
is the calls to __cpuid. Would the following simple tweak work, without
getting overly complex into adding EAL functions for generic cpu
identification. Replace the simple #include <cpuid.h> with:

	#ifdef RTE_ARCH_X86
	#include <cpuid.h>
	#else
	#define __cpuid(n, a, b, c, d) do { a = b = c = d =n; } while(0)
	#endif

[Obviously, the contents of the do-while can be modified depending on what
the compiler looks for in terms of modifying vars.]

Regards,
/Bruce