linux-kernel - Re: [PATCH V7 5/7] ACPI: Delay the enumeration on the devices whose dependency has not met

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Date:   Thu, 16 Mar 2017 11:13:01 +0100
From:   Arnd Bergmann <arnd@...db.de>
To:     "zhichang.yuan" <yuanzhichang@...ilicon.com>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>,
        Catalin Marinas <catalin.marinas@....com>,
        Will Deacon <will.deacon@....com>,
        Rob Herring <robh+dt@...nel.org>,
        Frank Rowand <frowand.list@...il.com>,
        Bjorn Helgaas <bhelgaas@...gle.com>,
        Rafael Wysocki <rafael@...nel.org>,
        Mark Rutland <mark.rutland@....com>,
        Linux ARM <linux-arm-kernel@...ts.infradead.org>,
        ACPI Devel Maling List <linux-acpi@...r.kernel.org>,
        Lorenzo Pieralisi <lorenzo.pieralisi@....com>,
        Benjamin Herrenschmidt <benh@...nel.crashing.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
        linuxarm@...wei.com, devicetree@...r.kernel.org,
        linux-pci <linux-pci@...r.kernel.org>,
        linux-serial@...r.kernel.org, Corey Minyard <minyard@....org>,
        liviu.dudau@....com, Zou Rongrong <zourongrong@...il.com>,
        John Garry <john.garry@...wei.com>,
        Gabriele Paoloni <gabriele.paoloni@...wei.com>,
        zhichang.yuan02@...il.com, kantyzc@....com,
        Wei Xu <xuwei5@...ilicon.com>
Subject: Re: [PATCH V7 5/7] ACPI: Delay the enumeration on the devices whose
 dependency has not met

On Thu, Mar 16, 2017 at 3:21 AM, zhichang.yuan
<yuanzhichang@...ilicon.com> wrote:
> Hi, Rafael,
>
> Thanks for your review!
>
> On 2017/3/14 5:24, Rafael J. Wysocki wrote:
>> On Monday, March 13, 2017 10:42:41 AM zhichang.yuan wrote:
>>> In commit 40e7fcb1929(ACPI: Add _DEP support to fix battery issue on Asus
>>> T100TA), the '_DEP' was supported to solve the dependency of Asus battery. But
>>> this patch is specific to Asus battery device.
>>> In the real world, there are other devices which need the dependency to play the
>>> role on the enumeration order. For example, all the Hip06 LPC
>>> periperals(IPMI-BT, uart, etc) must be scanned after the LPC host driver
>>> finished the probing. So, it makes sense to add a checking whether the ACPI
>>> device meet all the dependencies during its enumeration slot, if not, the
>>> enumeration will be delayed till all dependency master finish their work.
>>>
>>> This patch adds the dependency checking in ACPI enumeration, also the
>>> corresponding handling to retrigger the Hip06 LPC peripherals' scanning.
>>
>> AFAICS, _DEP is generally abused in the wild and cannot be made generic.  Sorry.
>>
>
> From the ACPI specification, _DEP is for operation region accesses.
> You are right...
>
> How about we add a ACPI handler for our LPC bus?? Just like amba.
> In this way, we also can solve the issue about LPC enumeration order.

As far as I can tell, PCI and LPC have exactly the same requirement here,
so whatever you end up doing for one should be used for the other as well.

      Arnd