linux-kernel - RE: [PATCH V4 0/3] Use efi_rts_wq to invoke EFI Runtime Services

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Date:   Sun, 27 May 2018 15:47:23 +0000
From:   "Prakhya, Sai Praneeth" <sai.praneeth.prakhya@...el.com>
To:     Ard Biesheuvel <ard.biesheuvel@...aro.org>
CC:     "linux-efi@...r.kernel.org" <linux-efi@...r.kernel.org>,
        "Linux Kernel Mailing List" <linux-kernel@...r.kernel.org>,
        Lee Chun-Yi <jlee@...e.com>, Borislav Petkov <bp@...en8.de>,
        "Luck, Tony" <tony.luck@...el.com>,
        "Will Deacon" <will.deacon@....com>,
        "Hansen, Dave" <dave.hansen@...el.com>,
        "Mark Rutland" <mark.rutland@....com>,
        Bhupesh Sharma <bhsharma@...hat.com>,
        "Naresh Bhat" <naresh.bhat@...aro.org>,
        "Neri, Ricardo" <ricardo.neri@...el.com>,
        Peter Zijlstra <peterz@...radead.org>,
        "Shankar, Ravi V" <ravi.v.shankar@...el.com>,
        Matt Fleming <matt@...eblueprint.co.uk>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        Miguel Ojeda <miguel.ojeda.sandonis@...il.com>
Subject: RE: [PATCH V4 0/3] Use efi_rts_wq to invoke EFI Runtime Services

> > Another follow on question is, does every firmware support both
> > blocking and non-blocking variants (specially legacy EFI firmware)? I
> > am worried about this because, presently efi_delete_dummy_variable()
> > uses set_variable() and
> > query_variable_info() but if I change efi_delete_dummy_variable() to
> > use non-blocking variants and if they aren’t supported, then, I guess,
> > efi_delete_dummy_variable() might fail :(
> >
> > So, could you please clarify on that?
> >
> 
> I don't follow. Why should it make any difference to the firmware whether the
> OS routines blocks or gives up? We always honor the mutual exclusion between
> different invocations of runtime services, and the firmware itself has no
> awareness of the kind of scheduling the OS needs to do to ensure this.

Sorry! my bad.. I thought firmware (with EFI System table revision > 2.0 ) offers two 
types of efi run time services, a blocking variant and a non-blocking variant. But, now I 
noticed in the spec that there is only set_variable() but _no_ set_variable_nonblocking(). 
Same with query_variable_info(). The same is also seen in runtime-wrappers.c file. 
Both the blocking and non-blocking variants call the same efi runtime service. I see that 
non-blocking() variants are just an additional feature (API) offered by OS.

Regards,
Sai