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From:   Michael Ellerman <mpe@ellerman.id.au>
To:     Hari Bathini <hbathini@linux.ibm.com>,
        Andrew Morton <akpm@linux-foundation.org>
Cc:     Pingfan Liu <piliu@redhat.com>,
        Kexec-ml <kexec@lists.infradead.org>,
        Mimi Zohar <zohar@linux.ibm.com>,
        Nayna Jain <nayna@linux.ibm.com>,
        Petr Tesarik <ptesarik@suse.cz>,
        Mahesh J Salgaonkar <mahesh@linux.ibm.com>,
        Sourabh Jain <sourabhjain@linux.ibm.com>,
        lkml <linux-kernel@vger.kernel.org>,
        linuxppc-dev <linuxppc-dev@ozlabs.org>,
        Eric Biederman <ebiederm@xmission.com>,
        Thiago Jung Bauermann <bauerman@linux.ibm.com>,
        Dave Young <dyoung@redhat.com>, Vivek Goyal <vgoyal@redhat.com>
Subject: Re: [RESEND PATCH v5 07/11] ppc64/kexec_file: enable early kernel's OPAL calls
In-Reply-To: <23baef6a-6ddc-572a-82c5-21a7fa441485@linux.ibm.com>
References: <159579157320.5790.6748078824637688685.stgit@hbathini> <159579233676.5790.10701756666641782647.stgit@hbathini> <87365b7nx4.fsf@mpe.ellerman.id.au> <23baef6a-6ddc-572a-82c5-21a7fa441485@linux.ibm.com>
Date:   Wed, 29 Jul 2020 11:15:12 +1000
Message-ID: <87v9i75dgf.fsf@mpe.ellerman.id.au>
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Hari Bathini <hbathini@linux.ibm.com> writes:
> On 28/07/20 7:16 pm, Michael Ellerman wrote:
>> Hari Bathini <hbathini@linux.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.

Ugh, OK.

> 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.

cheers