Hello Segher,
Thanks for your review and suggestions!
Segher Boessenkool <seg...@kernel.crashing.org> writes:
> (Sorry to hijack your reply).
>
> On Thu, Jul 18, 2019 at 06:11:48PM +1000, Alexey Kardashevskiy wrote:
>> On 13/07/2019 16:00, Thiago Jung Bauermann wrote:
>> >From: Ram Pai <linux...@us.ibm.com>
>> >+static int enter_secure_mode(unsigned long kbase, unsigned long fdt)
>> >+{
>> >+ register uint64_t func asm("r3") = UV_ESM;
>> >+ register uint64_t arg1 asm("r4") = (uint64_t)kbase;
>> >+ register uint64_t arg2 asm("r5") = (uint64_t)fdt;
>>
>> What does UV do with kbase and fdt precisely? Few words in the commit
>> log will do.
>>
>> >+
>> >+ asm volatile("sc 2\n"
>> >+ : "=r"(func)
>> >+ : "0"(func), "r"(arg1), "r"(arg2)
>> >+ :);
>> >+
>> >+ return (int)func;
>>
>> And why "func"? Is it "function"? Weird name. Thanks,
Yes, I believe func is for function. Perhaps ucall would be clearer
if the variable wasn't reused for the return value as Segher points out.
> Maybe the three vars should just be called "r3", "r4", and "r5" --
> r3 is used as return value as well, so "func" isn't a great name for it.
Yes, that does seem simpler.
> Some other comments about this inline asm:
>
> The "\n" makes the generated asm look funny and has no other function.
> Instead of using backreferences you can use a "+" constraint, "inout".
> Empty clobber list is strange.
> Casts to the return type, like most other casts, are an invitation to
> bugs and not actually useful.
>
> So this can be written
>
> static int enter_secure_mode(unsigned long kbase, unsigned long fdt)
> {
> register uint64_t r3 asm("r3") = UV_ESM;
> register uint64_t r4 asm("r4") = kbase;
> register uint64_t r4 asm("r5") = fdt;
>
> asm volatile("sc 2" : "+r"(r3) : "r"(r4), "r"(r5));
>
> return r3;
> }
I'll adopt your version, it is cleaner inded. Thanks for providing it!
> (and it probably should use u64 instead of both uint64_t and unsigned long?)
Almost all of prom_init.c uses unsigned long, with u64 in just a few
places. uint64_t isn't used anywhere else in the file. I'll switch to
unsigned long everywhere, since this feature is only for 64 bit.
--
Thiago Jung Bauermann
IBM Linux Technology Center
