Andi,
On Sat, 20 Oct 2018, Andi Kleen wrote:
> On Sat, Oct 20, 2018 at 10:19:37AM +0200, Thomas Gleixner wrote:
> > On Fri, 19 Oct 2018, Andi Kleen wrote:
> > There is no point to return the pointer because it's not a compound
> > structure. If you want to provide the possibility to use the index then
> > return the index and an error code if it does not match.
>
> It will be useful with the driver_data pointer, which you short sightedly
> forced me to remove, and likely will need to be readded at some point
> anyways if this gets more widely used.
It's good and established practice not to add functionality on a 'might be
used' basis. If you'd provide at least one or two patches which demonstrate
how that is useful then that would be convincing.
> At least with the pointer not all callers will need to be changed then.
It doesn't need to be changed at all, when done correctly.
So lets walk through that again:
1) x86_match_microcode() is a misnomer because it's not as the name
suggests a match function. It compares whether the micro code revision
is greater or equal the minimal required micro code revision for the
current CPU.
2) None of the existing implementations needs a pointer return value,
neither does your use case at hand.
3) If this should be extended to a generic cpu id matching facility, then
it can be very well designed so. See below.
Step 1:
struct x86_cpu_check {
u8 vendor;
u8 family;
u8 model;
u8 stepping;
};
struct x86_cpu_check *x86_match_cpu(struct x86_cpu_check *table)
{
// Find matching vendor, family, model, stepping entry
... {
return entry;
}
return NULL;
}
Genuine CPU match function, which can be extended by extending the data
structure.
Step 2:
struct x86_cpu_check {
u8 vendor;
u8 family;
u8 model;
u8 stepping;
u32 microcode_rev;
};
bool x86_cpu_has_min_microcode(struct x86_cpu_check *table)
{
struct x86_cpu_check *res = x86_match_cpu(table);
if (!res)
return false;
return res->microcode_revision >= boot_cpu_data.microcode;
}
Step 3:
struct x86_cpu_check {
u8 vendor;
u8 family;
u8 model;
u8 stepping;
union {
u32 microcode_rev;
void *driver_data;
}
};
Can be used with x86_match_cpu() for all non microcode based matching.
So if you really need something which checks the microcode and provides the
pointer, then it's easy enough to do:
Step 4:
struct x86_cpu_check {
u8 vendor;
u8 family;
u8 model;
u8 stepping;
u32 microcode_rev;
void *driver_data;
};
struct x86_cpu_check *x86_check_min_microcode(struct x86_cpu_check *table)
{
struct x86_cpu_check *res = x86_match_cpu(table);
if (!res || res->microcode_rev < boot_cpu_data.microcode)
return NULL;
return res;
}
static inline bool x86_cpu_has_min_microcode(struct x86_cpu_check *table)
{
return !!x86_check_min_microcode(table);
}
None of these steps requires to change a call site or a table.
But probably I'm too short sighted and missing something crucial. Looking
forward for enlightment.
> Also it's symmetric with how the PCI and USB and the existing x86 match
> discovery interfaces work.
And the point is? That we need to keep everything as we've done it 20 years
ago?
> > > > VENDOR_INTEL = 0, so this check is obscure to begin with. Either you
> > > > chose
> > > > a explicit condition to put at the end of the table, e.g. vendor =
> > > > U8_MAX
> > > > or you hand in the array size to the function.
> > >
> > > That would both be awkward. It's the same as match_cpu, and 0 terminators
> > > are standard practice in practical all similar code. I removed
> > > the or with the family.
> >
> > That's debatable because it's more easy to miss the terminator than getting
> > the ARRAY_SIZE() argument wrong. But it doesn't matter much.
>
> Ok then please apply it.
Sure, once this argument is settled and all review comments are addressed.
Thanks,
tglx
