linux-kernel - Re: [PATCH v2 2/2] RISC-V: Consolidate isa correctness check

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Date:   Fri, 18 Oct 2019 11:25:19 -0700 (PDT)
From:   Paul Walmsley <paul.walmsley@...ive.com>
To:     Atish Patra <Atish.Patra@....com>
cc:     "linux-riscv@...ts.infradead.org" <linux-riscv@...ts.infradead.org>,
        "gregkh@...uxfoundation.org" <gregkh@...uxfoundation.org>,
        "info@...ux.net" <info@...ux.net>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "rfontana@...hat.com" <rfontana@...hat.com>,
        "johan@...nel.org" <johan@...nel.org>,
        "anup@...infault.org" <anup@...infault.org>,
        "tglx@...utronix.de" <tglx@...utronix.de>,
        "palmer@...ive.com" <palmer@...ive.com>,
        "aou@...s.berkeley.edu" <aou@...s.berkeley.edu>,
        "allison@...utok.net" <allison@...utok.net>
Subject: Re: [PATCH v2  2/2] RISC-V: Consolidate isa correctness check

On Fri, 18 Oct 2019, Atish Patra wrote:

> On Fri, 2019-10-18 at 01:43 -0700, Paul Walmsley wrote:
> > On Wed, 9 Oct 2019, Atish Patra wrote:
> > 
> > > Currently, isa string is read and checked for correctness at 
> > > multiple places.
> > > 
> > > Consolidate them into one function and use it only during early 
> > > bootup. In case of a incorrect isa string, the cpu shouldn't boot at 
> > > all.
> > > 
> > > Signed-off-by: Atish Patra <atish.patra@....com>
> > 
> > Looks like riscv_read_check_isa() is called twice for each hart.  Is 
> > there any way to call it only once per hart?
> > 
> 
> I had to add the check in riscv_fill_hwcap() because that function is
> iterating over all cpu nodes to set the hwcap. Thus, some of the harts
> that are not available due to incorrect isa string can affect hwcap.
> 
> We can check cpu_possible_mask to figure out the harts with invalid isa
> strings but that will perform poorly as RISC-V have more harts in
> future.

How about just calling riscv_read_check_isa() once for all harts and 
leaving riscv_fill_hwcap() the way it was?  You'll probably need to hoist 
the earlier call out of setup_smp(), so it still is called when 
!CONFIG_SMP.


- Paul