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Date: Mon, 11 Nov 2024 14:14:48 -0600
From: Bjorn Helgaas <helgaas@kernel.org>
To: Shijith Thotton <sthotton@marvell.com>
Cc: bhelgaas@google.com, ilpo.jarvinen@linux.intel.com,
	Jonathan.Cameron@huawei.com, linux-kernel@vger.kernel.org,
	linux-pci@vger.kernel.org, rafael@kernel.org,
	scott@os.amperecomputing.com, jerinj@marvell.com,
	schalla@marvell.com, vattunuru@marvell.com
Subject: Re: [PATCH v4] PCI: hotplug: Add OCTEON PCI hotplug controller driver
Message-ID: <20241111201448.GA1814761@bhelgaas>
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In-Reply-To: <20241111134523.2796699-1-sthotton@marvell.com>

On Mon, Nov 11, 2024 at 07:15:11PM +0530, Shijith Thotton wrote:
> This patch introduces a PCI hotplug controller driver for the OCTEON
> PCIe device. The OCTEON PCIe device is a multi-function device where the
> first function serves as the PCI hotplug controller.
> 
>                +--------------------------------+
>                |           Root Port            |
>                +--------------------------------+
>                                |
>                               PCIe
>                                |
> +---------------------------------------------------------------+
> |              OCTEON PCIe Multifunction Device                 |
> +---------------------------------------------------------------+
>              |                    |              |            |
>              |                    |              |            |
> +---------------------+  +----------------+  +-----+  +----------------+
> |      Function 0     |  |   Function 1   |  | ... |  |   Function 7   |
> | (Hotplug controller)|  | (Hotplug slot) |  |     |  | (Hotplug slot) |
> +---------------------+  +----------------+  +-----+  +----------------+
>              |
>              |
> +-------------------------+
> |   Controller Firmware   |
> +-------------------------+
> 
> The hotplug controller driver enables hotplugging of non-controller
> functions within the same device. During probing, the driver removes
> the non-controller functions and registers them as PCI hotplug slots.
> These slots are added back by the driver, only upon request from the
> device firmware.
> 
> The controller uses MSI-X interrupts to notify the host of hotplug
> events initiated by the OCTEON firmware. Additionally, the driver
> allows users to enable or disable individual functions via sysfs slot
> entries, as provided by the PCI hotplug framework.

Can we say something here about what the benefit of this driver is?
For example, does it save power?

What causes the function 0 firmware to request a hot-add or
hot-removal of another function?

Bjorn