linux-kernel - Re: [PATCH] PCI/ASPM: Enable ASPM for links under VMD domain

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Date:   Sat, 29 Aug 2020 08:24:05 +0100
From:   "hch@...radead.org" <hch@...radead.org>
To:     "Limonciello, Mario" <Mario.Limonciello@...l.com>
Cc:     "hch@...radead.org" <hch@...radead.org>,
        "Derrick, Jonathan" <jonathan.derrick@...el.com>,
        "wangxiongfeng2@...wei.com" <wangxiongfeng2@...wei.com>,
        "kw@...ux.com" <kw@...ux.com>,
        "hkallweit1@...il.com" <hkallweit1@...il.com>,
        "kai.heng.feng@...onical.com" <kai.heng.feng@...onical.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "Williams, Dan J" <dan.j.williams@...el.com>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "Huffman, Amber" <amber.huffman@...el.com>,
        "Wysocki, Rafael J" <rafael.j.wysocki@...el.com>
Subject: Re: [PATCH] PCI/ASPM: Enable ASPM for links under VMD domain

On Thu, Aug 27, 2020 at 05:49:40PM +0000, Limonciello, Mario wrote:
> Can you further elaborate what exactly you're wanting here?  VMD enable/disable
> is something that is configured in firmware setup as the firmware does the early
> configuration for the silicon related to it.  So it's up to the OEM whether to
> offer the knob to an end user.
> 
> At least for Dell this setting also does export to sysfs and can be turned on/off
> around a reboot cycle via this: https://patchwork.kernel.org/patch/11693231/.
> 
> As was mentioned earlier in this thread VMD is likely to be defaulting to "on"
> for many machines with the upcoming silicon.  Making it work well on Linux is
> preferable to again having to change firmware settings between operating systems
> like the NVME remapping thing from earlier silicon required.

And the right answer is to turn it off, but we really need to do that
at runtime, and not over a reboot cycle..