linux-kernel - Re: [RFC 0/9] PCIe Hotplug Slot Emulation driver

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Message-ID: <8a787f85964c66e8c6efde51f439db26fecfc5c6.camel@intel.com>
Date:   Mon, 10 Feb 2020 17:09:59 +0000
From:   "Derrick, Jonathan" <jonathan.derrick@...el.com>
To:     "hch@....de" <hch@....de>
CC:     "Shevchenko, Andriy" <andriy.shevchenko@...el.com>,
        "lorenzo.pieralisi@....com" <lorenzo.pieralisi@....com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "mika.westerberg@...ux.intel.com" <mika.westerberg@...ux.intel.com>,
        "Baldysiak, Pawel" <pawel.baldysiak@...el.com>,
        "helgaas@...nel.org" <helgaas@...nel.org>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "mr.nuke.me@...il.com" <mr.nuke.me@...il.com>,
        "kbusch@...nel.org" <kbusch@...nel.org>,
        "okaya@...nel.org" <okaya@...nel.org>
Subject: Re: [RFC 0/9] PCIe Hotplug Slot Emulation driver

On Mon, 2020-02-10 at 17:58 +0100, hch@....de wrote:
> On Mon, Feb 10, 2020 at 03:05:47PM +0000, Derrick, Jonathan wrote:
> > > The code seems like one giant hack to me.  What is the real life
> > > use case for this?  Another Intel chipset fuckup like vmd or the ahci
> > > remapping?
> > > 
> > Exactly as the cover letter describes. An interposer being used on a
> > non-hotplug slot.
> 
> That isn't a use a case, that iѕ a description of the implementation.
> Why would you want this code?
It allows non-hotplug slots to take advantage of the kernel's robust
hotplug ecosystem, if the platform configuration can tolerate the
events. This could also reduce BOM cost by eliminating some slot
controllers. Say you had something that only needed to be hotplugged
very infrequently, like RAIDed OS drives, versus something needing to
be hotplugged very frequently like data drives.


Granted it probably could be fit into pciehp_poll, but it seemed to
have a different objective (emulating slot)