Re: [PATCH RFC v2 0/4] PCI: pciehp: Do not turn off slot if presence comes up after link

From: Bjorn Helgaas <helgaas@kernel.org>
To: Alexandru Gagniuc <mr.nuke.me@gmail.com>
Cc: austin_bolen@dell.com, alex_gagniuc@dellteam.com,
	keith.busch@intel.com, Shyam_Iyer@Dell.com, lukas@wunner.de,
	okaya@kernel.org, linux-pci@vger.kernel.org
Subject: Re: [PATCH RFC v2 0/4] PCI: pciehp: Do not turn off slot if presence comes up after link
Date: Thu, 18 Apr 2019 19:01:49 -0500	[thread overview]
Message-ID: <20190419000148.GI126710@google.com> (raw)
In-Reply-To: <20190220012031.10741-1-mr.nuke.me@gmail.com>

Hi Alex,

This has languished a long time (sorry about that), and there were
several review comments.  I know you wanted my opinion on strategy,
but would you mind posting a fresh version with the fixes you've
already done and rebased to v5.1-rc1?

On Tue, Feb 19, 2019 at 07:20:26PM -0600, Alexandru Gagniuc wrote:
> If the presence detect state (PDS) becomes active after the link
> comes up (DLLLA), the hotplug code removes the device and then
> re-loads the driver. For most devices, this is a mere inconvenience,
> and for PCIe storage devices that are part of a RAID set which started
> rebuilding, it can get fun.
> 
> Ideally, we wouldn't remove perfectly good devices. According to
> the old PCIe spec PDS would always have to come up at or before DLLLA.
> Since not everyone followed this (looking at you Dell and HPE!!!!),
> this now got standardized in PCIe 4.0. (*).
> 
> This series has two solutions for this problem, and is intended to
> serve as a bikeshedding point for which is better:
>  1. Try to wait for PDS _before_ loading the driver
>  2. Load as usual, and recognize the delayed PDS event as such
> 
> I think (2) is more generic and elegant, but a lot of people seem to
> like something similar to (1).
> 
> (*) ECN was approved in Nov 2018, and is normative spec text. A lot of
> the leaked PCIe 4.0 specs do not have this change.
> 
> 
> 
> Alexandru Gagniuc (4):
>   PCI: hotplug: Add support for disabling in-band presence
>   PCI: pciehp: Do not turn off slot if presence comes up after link
>   PCI: hotplug: Wait for PDS when in-band presence is disabled
>   PCI: hotplug: Add quirk For Dell nvme pcie switches
> 
>  drivers/pci/hotplug/pciehp.h      |  1 +
>  drivers/pci/hotplug/pciehp_ctrl.c | 24 ++++++++++++++
>  drivers/pci/hotplug/pciehp_hpc.c  | 54 ++++++++++++++++++++++++++++++-
>  include/linux/pci.h               |  1 +
>  include/uapi/linux/pci_regs.h     |  2 ++
>  5 files changed, 81 insertions(+), 1 deletion(-)
> 
> -- 
> 2.19.2
> 