From: Frank Rowand <frowand.list@gmail.com>
To: "Andy Shevchenko" <andriy.shevchenko@linux.intel.com>,
"Clément Léger" <clement.leger@bootlin.com>
Cc: Rob Herring <robh+dt@kernel.org>,
Pantelis Antoniou <pantelis.antoniou@konsulko.com>,
Bjorn Helgaas <bhelgaas@google.com>,
Allan Nielsen <allan.nielsen@microchip.com>,
Horatiu Vultur <horatiu.vultur@microchip.com>,
Steen Hegelund <steen.hegelund@microchip.com>,
Thomas Petazzoni <thomas.petazonni@bootlin.com>,
Alexandre Belloni <alexandre.belloni@bootlin.com>,
Mark Brown <broonie@kernel.org>, Jakub Kicinski <kuba@kernel.org>,
Hans de Goede <hdegoede@redhat.com>, Andrew Lunn <andrew@lunn.ch>,
devicetree@vger.kernel.org, linux-kernel@vger.kernel.org,
linux-pci@vger.kernel.org
Subject: Re: [PATCH 0/3] add dynamic PCI device of_node creation for overlay
Date: Mon, 9 May 2022 15:11:53 -0500 [thread overview]
Message-ID: <b476913d-896d-309c-f304-3ab37b81b4a9@gmail.com> (raw)
In-Reply-To: <YnlIs312R4Temgu3@smile.fi.intel.com>
On 5/9/22 12:00, Andy Shevchenko wrote:
> On Mon, May 09, 2022 at 06:09:17PM +0200, Clément Léger wrote:
>> Le Mon, 9 May 2022 10:56:36 -0500,
>> Frank Rowand <frowand.list@gmail.com> a écrit :
>
> ...
>
>>> On the surface, it appears that your need might be well met by having
>>> a base devicetree that describes all of the pcie nodes, but with each
>>> node having a status of "disabled" so that they will not be used.
>>> Have a devicetree overlay describing the pcie card (as you proposed),
>>> where the overlay also includes a status of "ok" for the pcie node.
>>> Applying the overlay, with a method of redirecting the target to a
>>> specific pcie node would change the status of the pcie node to enable
>>> its use. (You have already proposed a patch to modify
>>> of_overlay_fdt_apply() to allow a modified target, so not a new
>>> concept from me.) My suggestion is to apply the overlay devicetree
>>> to the base devicetree before the combined FDT devicetree is passed
>>> to the kernel at boot. The overlay apply could be done by several
>>> different entities. It could be before the bootloader executes, it
>>> could be done by the bootloader, it could be done by a shim between
>>> the bootloader and the kernel. This method avoids all of the issues
>>> of applying an overlay to a running system that I find problematic.
>>> It is also a method used by the U-boot bootloader, as an example.
>>
>> Ok, that is actually possible on a system that is given a device-tree
>> by the bootloader. But on a system that is desrcibed using ACPI (such
>> as the x86), this is much more difficult (at least to my knowledge)...
>> We want this feature to be easy to use for the end user. Adding such
>> configuration which also differs between various architecture is
>> clearly not so easy to setup.
>>
>> Moreover, since the PCI is meant to be "Plug and Play", such
>> configuration would completely break that. If the user switches the
>> PCIe card from one slot to another, the bootloader configuration will
>> need to be modified. This seems a big no way for me (and for the user).
>
> The main problem here is that Linux does not support hotplugging for the
> devices behind non-hotpluggable buses. You need to develop something to
> say that the device tree (in terms of hardware) can morph at run-time
> transparently to the user. I think the closest one is what FPGA does,
> or at least should do.
That is something I was not aware of yet. Is the card in question a
hotpluggable card? Do the systems that you anticipate plugging the
card into support hotplug?
-Frank
>
>>> The other big issue is mixing ACPI and devicetree on a single system.
>>> Historically, the Linux devicetree community has not been receptive
>>> to the ides of that mixture. Your example might be a specific case
>>> where the two can be isolated from each other, or maybe not. (For
>>> disclosure, I am essentially ACPI ignorant.) I suspect that mixing
>>> ACPI and devicetree is a recipe for disaster in the general case.
>>
>> Agreed, on that fact, it did raised some eyebrows, and it was for that
>> specific concern that initially, I proposed the fwnode solution.
>> Honestly, the fwnode conversion represent a lot of work (hundreds of
>> lines easily) + requires a conversion of all the subsystem that are not
>> fwnode ready (spoiler: almost all of them are not ready).
>
> In either case you need to provide a format that would be suitable for
> DT-based as well as ACPI-based platforms.
>
next prev parent reply other threads:[~2022-05-09 20:26 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-04-27 9:44 [PATCH 0/3] add dynamic PCI device of_node creation for overlay Clément Léger
2022-04-27 9:45 ` [PATCH 1/3] of: always populate a root node Clément Léger
2022-05-03 13:45 ` Rob Herring
2022-05-03 15:38 ` Clément Léger
2022-05-03 17:22 ` Frank Rowand
2022-05-17 3:11 ` Frank Rowand
2022-05-17 7:37 ` Clément Léger
2022-05-17 15:03 ` Frank Rowand
2022-05-18 10:03 ` Clément Léger
2022-04-27 9:45 ` [PATCH 2/3] PCI: of: create DT nodes for PCI devices if they do not exists Clément Léger
2022-04-27 17:37 ` kernel test robot
2022-04-27 17:47 ` kernel test robot
2022-05-03 14:12 ` Rob Herring
2022-05-03 16:05 ` Clément Léger
2022-05-03 22:53 ` Bjorn Helgaas
2022-05-04 13:43 ` Clément Léger
2022-05-18 19:22 ` Lizhi Hou
2022-04-27 9:45 ` [PATCH 3/3] of: overlay: add of_overlay_fdt_apply_to_node() Clément Léger
2022-05-06 18:33 ` [PATCH 0/3] add dynamic PCI device of_node creation for overlay Frank Rowand
2022-05-09 12:16 ` Clément Léger
2022-05-09 15:56 ` Frank Rowand
2022-05-09 16:09 ` Clément Léger
2022-05-09 17:00 ` Andy Shevchenko
2022-05-09 20:11 ` Frank Rowand [this message]
2022-05-09 20:40 ` Andy Shevchenko
2022-05-10 7:22 ` Christoph Hellwig
2022-05-09 20:07 ` Frank Rowand
2022-05-10 7:20 ` Clément Léger
2022-05-09 18:36 ` Rob Herring
2022-05-09 20:35 ` Frank Rowand
2022-05-10 14:43 ` Rob Herring
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