From: Sonal Santan <sonal.santan@amd.com>
To: Rob Herring <robh@kernel.org>, Frank Rowand <frowand.list@gmail.com>
Cc: Lizhi Hou <lizhi.hou@amd.com>,
linux-pci@vger.kernel.org, devicetree@vger.kernel.org,
linux-kernel@vger.kernel.org, helgaas@kernel.org,
clement.leger@bootlin.com, max.zhen@amd.com, larry.liu@amd.com,
brian.xu@amd.com, stefano.stabellini@xilinx.com, trix@redhat.com
Subject: Re: [PATCH RFC 0/2] Generate device tree node for pci devices
Date: Fri, 30 Sep 2022 12:29:40 -0700 [thread overview]
Message-ID: <8ea70992-d4e9-8bbd-0fca-d5700f84e071@amd.com> (raw)
In-Reply-To: <CAL_JsqJn=i=TT9NArHK25g1NkZN_G1GjN3EGEeTAvyW_PUhgcw@mail.gmail.com>
On 9/26/22 15:44, Rob Herring wrote:
> On Fri, Sep 16, 2022 at 6:15 PM Frank Rowand <frowand.list@gmail.com> wrote:
>>
>> On 8/29/22 16:43, Lizhi Hou wrote:
>>> This patch series introduces OF overlay support for PCI devices which
>>> primarily addresses two use cases. First, it provides a data driven method
>>> to describe hardware peripherals that are present in a PCI endpoint and
>>> hence can be accessed by the PCI host. An example device is Xilinx/AMD
>>> Alveo PCIe accelerators. Second, it allows reuse of a OF compatible
>>> driver -- often used in SoC platforms -- in a PCI host based system. An
>>> example device is Microchip LAN9662 Ethernet Controller.
>>>
>>> This patch series consolidates previous efforts to define such an
>>> infrastructure:
>>> https://lore.kernel.org/lkml/20220305052304.726050-1-lizhi.hou@xilinx.com/
>>> https://lore.kernel.org/lkml/20220427094502.456111-1-clement.leger@bootlin.com/
>>>
>>> Normally, the PCI core discovers PCI devices and their BARs using the
>>> PCI enumeration process. However, the process does not provide a way to
>>> discover the hardware peripherals that are present in a PCI device, and
>>> which can be accessed through the PCI BARs. Also, the enumeration process
>>> does not provide a way to associate MSI-X vectors of a PCI device with the
>>> hardware peripherals that are present in the device. PCI device drivers
>>> often use header files to describe the hardware peripherals and their
>>> resources as there is no standard data driven way to do so. This patch> series proposes to use flattened device tree blob to describe the
>>> peripherals in a data driven way.
>>
>>> Based on previous discussion, using
>>> device tree overlay is the best way to unflatten the blob and populate
>>> platform devices.
>>
>> I still do not agree with this statement. The device tree overlay
>> implementation is very incomplete and should not be used until it
>> becomes more complete. No need to debate this right now, but I don't want
>> to let this go unchallenged.
>
> Then we should remove overlay support. The only way it becomes more
> complete is having actual users.
>
> But really, whether this is the right solution to the problem is
> independent of the state of kernel overlay support.
>
>> If there is no base system device tree on an ACPI based system, then I
>> am not convinced that a mixed ACPI / device tree implementation is
>> good architecture.
>
> Most/all of this series is needed for a DT system in which the PCI
> devices are not populated in the DT.
>
>> I might be more supportive of using a device tree
>> description of a PCI device in a detached device tree (not linked to
>> the system device tree, but instead freestanding). Unfortunately the
>> device tree functions assume a single system devicetree, with no concept
>> of a freestanding tree (eg, if a NULL device tree node is provided to
>> a function or macro, it often defaults to the root of the system device
>> tree). I need to go look at whether the flag OF_DETACHED handles this,
>> or if it could be leveraged to do so.
>
> Instead of worrying about a theoretical problem, we should see if
> there is an actual problem for a user.
>
> I'm not so worried about DT functions themselves, but places which
> have 'if ACPI ... else (DT) ...' paths.
>
Bringing this thread back into focus. Any thoughts on how to move forward?
-Sonal
> Rob
next prev parent reply other threads:[~2022-09-30 19:29 UTC|newest]
Thread overview: 37+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-08-29 21:43 [PATCH RFC 0/2] Generate device tree node for pci devices Lizhi Hou
2022-08-29 21:43 ` [PATCH RFC 1/2] of: dynamic: add of_node_alloc() Lizhi Hou
2022-09-16 23:15 ` Frank Rowand
2022-08-29 21:43 ` [PATCH RFC 2/2] pci: create device tree node for selected devices Lizhi Hou
2022-09-02 18:54 ` Rob Herring
2022-09-12 6:33 ` Frank Rowand
2022-09-13 7:03 ` Frank Rowand
2022-09-16 23:20 ` Frank Rowand
2022-09-13 5:49 ` Lizhi Hou
2022-09-02 20:43 ` [PATCH RFC 0/2] Generate device tree node for pci devices Bjorn Helgaas
2022-09-09 23:06 ` Lizhi Hou
2022-09-13 7:00 ` Frank Rowand
2022-09-13 17:10 ` Lizhi Hou
2022-09-13 17:41 ` Frank Rowand
2022-09-13 21:02 ` Lizhi Hou
2022-09-17 2:23 ` Frank Rowand
2022-09-17 18:36 ` Tom Rix
2022-09-20 3:12 ` Frank Rowand
2022-09-26 3:03 ` Sonal Santan
2022-10-14 21:25 ` Frank Rowand
2022-10-10 8:42 ` [PATCH RFC 0/2] Generate device tree node for pci devicesgain, Clément Léger
2022-10-13 6:05 ` Frank Rowand
2022-10-13 8:02 ` Clément Léger
2022-10-13 17:28 ` Frank Rowand
2022-10-14 17:33 ` Rob Herring
2022-10-14 18:52 ` Frank Rowand
2022-10-17 7:18 ` Clément Léger
2022-10-26 21:20 ` Sonal Santan
2022-09-14 13:35 ` [PATCH RFC 0/2] Generate device tree node for pci devices Jeremi Piotrowski
2022-09-14 18:08 ` Rob Herring
2022-09-16 23:15 ` Frank Rowand
2022-09-26 22:44 ` Rob Herring
2022-09-30 19:29 ` Sonal Santan [this message]
2022-10-06 15:10 ` Rob Herring
2022-10-07 22:45 ` Sonal Santan
2022-10-10 8:58 ` Clément Léger
2022-10-13 6:08 ` Frank Rowand
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