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Subject: Re: [PATCH] PCI/ASPM: Enable ASPM for links under VMD domain
From:   Kai Heng Feng <kai.heng.feng@canonical.com>
In-Reply-To: <20200825062320.GA27116@infradead.org>
Date:   Tue, 25 Aug 2020 14:39:55 +0800
Cc:     Bjorn Helgaas <bhelgaas@google.com>, jonathan.derrick@intel.com,
        Mario.Limonciello@dell.com, Heiner Kallweit <hkallweit1@gmail.com>,
        Mika Westerberg <mika.westerberg@linux.intel.com>,
        "Rafael J. Wysocki" <rafael.j.wysocki@intel.com>,
        Xiongfeng Wang <wangxiongfeng2@huawei.com>,
        Krzysztof Wilczynski <kw@linux.com>,
        "open list:PCI SUBSYSTEM" <linux-pci@vger.kernel.org>,
        open list <linux-kernel@vger.kernel.org>,
        Dan Williams <dan.j.williams@intel.com>,
        "Huffman, Amber" <amber.huffman@intel.com>
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References: <20200821123222.32093-1-kai.heng.feng@canonical.com>
 <20200825062320.GA27116@infradead.org>
To:     Christoph Hellwig <hch@infradead.org>
Sender: linux-kernel-owner@vger.kernel.org
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Hi Christoph,

> On Aug 25, 2020, at 2:23 PM, Christoph Hellwig <hch@infradead.org> wrote:
> 
> On Fri, Aug 21, 2020 at 08:32:20PM +0800, Kai-Heng Feng wrote:
>> New Intel laptops with VMD cannot reach deeper power saving state,
>> renders very short battery time.
> 
> So what about just disabling VMD given how bloody pointless it is?
> Hasn't anyone learned from the AHCI remapping debacle?
> 
> I'm really pissed at all this pointless crap intel comes up with just
> to make life hard for absolutely no gain.  Is it so hard to just leave
> a NVMe device as a standard NVMe device instead of f*^&ing everything
> up in the chipset to make OS support a pain and I/O slower than by
> doing nothing?

From what I can see from the hardwares at my hand, VMD only enables a PCI domain and PCI bridges behind it.

NVMe works as a regular NVMe under those bridges. No magic remapping happens here.

Kai-Heng