From mboxrd@z Thu Jan 1 00:00:00 1970 From: will.deacon@arm.com (Will Deacon) Date: Wed, 10 Sep 2014 14:04:19 +0100 Subject: [PATCH v3 04/17] ARM64 / ACPI: Introduce early_param for "acpi" In-Reply-To: <540F7BE2.8060403@redhat.com> References: <1409583475-6978-1-git-send-email-hanjun.guo@linaro.org> <1409583475-6978-5-git-send-email-hanjun.guo@linaro.org> <540F7BE2.8060403@redhat.com> Message-ID: <20140910130419.GJ28488@arm.com> To: linux-arm-kernel@lists.infradead.org List-Id: linux-arm-kernel.lists.infradead.org On Tue, Sep 09, 2014 at 11:14:58PM +0100, Jon Masters wrote: > On 09/09/2014 01:17 PM, Bjorn Helgaas wrote: > > On Mon, Sep 1, 2014 at 8:57 AM, Hanjun Guo wrote: > >> From: Al Stone > >> > >> Introduce one early parameters "off" for "acpi" to disable ACPI on > >> ARM64. > > > > It might be worth mentioning the purpose of this in the changelog (and > > maybe the documentation). I don't think this parameter is supported > > on ia64, and on x86 it seems like it's mostly used as a "fix" by > > Ubuntu users who consider the problem resolved when they find this > > parameter. That just means we don't get a chance to fix the real > > underlying problem, so I'm not sure it's a real benefit to have the > > parameter. > > >> - acpi= [HW,ACPI,X86] > >> + acpi= [HW,ACPI,X86,ARM] > >> Advanced Configuration and Power Interface > >> Format: { force | off | strict | noirq | rsdt } > >> force -- enable ACPI if default was off > >> @@ -175,6 +175,7 @@ bytes respectively. Such letter suffixes can also be entirely omitted. > >> strictly ACPI specification compliant. > >> rsdt -- prefer RSDT over (default) XSDT > >> copy_dsdt -- copy DSDT to memory > >> + For ARM64, ONLY "acpi=off" is available. > > Something along the lines of: > > "The purpose of disabling ACPI on 64-bit ARM server platforms is to > allow for an orderly adoption of ACPI on early systems that may also > provide a DeviceTree based boot option initially. The acpi= option > disables both parsing of any tables passed in through the EFI System > Table RSDP and also disables the runtime ACPI interpreter on arm64". Please, let's keep this polarised rhetoric out of the Linux kernel. If ACPI support gets merged for arm64, then the community has a commitment to support it alongside devicetree. There isn't a migration path because nothing is being replaced and we shouldn't dictate to users in which circumstances they are allowed to use one firmware interface over another. Other entities (server vendors, distributions, firmware guys, ...) can make up their own rules, but attempting to peddle their agenda in the upstream kernel is completely inappropriate. It's blindingly obvious that acpi=off is there to disable ACPI at boot. We either support that option or we don't -- none of this `oh, well you can use it in this specific case I suppose' rubbish. I'm not questioning your use-case, but there's really no need to talk about an `orderly adoption' when all you need to say is that your ACPI is busted and passing acpi=off lets you boot with a devicetree. Yes, I'm being pedantic, but it's really important not to get the upstream messaging wrong about ACPI. Devicetree is absolutely *not* going away and people can choose to use whatever they prefer, however they prefer to use it. Will