linux-kernel - Re: [RESEND PATCH v5 07/11] ppc64/kexec_file: enable early kernel's OPAL calls

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Message-ID: <23baef6a-6ddc-572a-82c5-21a7fa441485@linux.ibm.com>
Date:   Wed, 29 Jul 2020 00:54:47 +0530
From:   Hari Bathini <hbathini@...ux.ibm.com>
To:     Michael Ellerman <mpe@...erman.id.au>,
        Andrew Morton <akpm@...ux-foundation.org>
Cc:     Pingfan Liu <piliu@...hat.com>,
        Kexec-ml <kexec@...ts.infradead.org>,
        Mimi Zohar <zohar@...ux.ibm.com>,
        Nayna Jain <nayna@...ux.ibm.com>,
        Petr Tesarik <ptesarik@...e.cz>,
        Mahesh J Salgaonkar <mahesh@...ux.ibm.com>,
        Sourabh Jain <sourabhjain@...ux.ibm.com>,
        lkml <linux-kernel@...r.kernel.org>,
        linuxppc-dev <linuxppc-dev@...abs.org>,
        Eric Biederman <ebiederm@...ssion.com>,
        Thiago Jung Bauermann <bauerman@...ux.ibm.com>,
        Dave Young <dyoung@...hat.com>, Vivek Goyal <vgoyal@...hat.com>
Subject: Re: [RESEND PATCH v5 07/11] ppc64/kexec_file: enable early kernel's
 OPAL calls



On 28/07/20 7:16 pm, Michael Ellerman wrote:
> Hari Bathini <hbathini@...ux.ibm.com> writes:
>> Kernel built with CONFIG_PPC_EARLY_DEBUG_OPAL enabled expects r8 & r9
>> to be filled with OPAL base & entry addresses respectively. Setting
>> these registers allows the kernel to perform OPAL calls before the
>> device tree is parsed.
> 
> I'm not convinced we want to do this.
> 
> If we do it becomes part of the kexec ABI and we have to honour it into
> the future.
> 
> And in practice there are no non-development kernels built with OPAL early
> debugging enabled, so it's not clear it actually helps anyone other than
> developers.
> 

Hmmm.. kexec-tools does it since commit d58ad564852c ("kexec/ppc64
Enable early kernel's OPAL calls") for kexec_load syscall. So, we would
be breaking kexec ABI either way, I guess.

Let me put this patch at the end of the series in the respin to let you
decide whether to have it or not..

Thanks
Hari