linux-kernel - Re: [PATCH v19 01/10] PCI: endpoint: Set ID and of

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Message-ID: <75opnvi46fbmsnmykjwn3gmir7r3uqhzp7tfoua42cado6aopu@dmos2v2qd3jn>
Date: Wed, 2 Jul 2025 20:25:17 +0530
From: Manivannan Sadhasivam <mani@...nel.org>
To: Frank Li <Frank.li@....com>
Cc: Kishon Vijay Abraham I <kishon@...nel.org>, 
	"Rafael J. Wysocki" <rafael@...nel.org>, Thomas Gleixner <tglx@...utronix.de>, 
	Anup Patel <apatel@...tanamicro.com>, Marc Zyngier <maz@...nel.org>, 
	Greg Kroah-Hartman <gregkh@...uxfoundation.org>, Danilo Krummrich <dakr@...nel.org>, 
	Bjorn Helgaas <bhelgaas@...gle.com>, Arnd Bergmann <arnd@...db.de>, Shuah Khan <shuah@...nel.org>, 
	Richard Zhu <hongxing.zhu@....com>, Lucas Stach <l.stach@...gutronix.de>, 
	Lorenzo Pieralisi <lpieralisi@...nel.org>, Rob Herring <robh@...nel.org>, Shawn Guo <shawnguo@...nel.org>, 
	Sascha Hauer <s.hauer@...gutronix.de>, Pengutronix Kernel Team <kernel@...gutronix.de>, 
	Fabio Estevam <festevam@...il.com>, Krzysztof Kozlowski <krzk+dt@...nel.org>, 
	Conor Dooley <conor+dt@...nel.org>, Krzysztof Wilczyński <kwilczynski@...nel.org>, 
	Niklas Cassel <cassel@...nel.org>, dlemoal@...nel.org, jdmason@...zu.us, 
	linux-kernel@...r.kernel.org, linux-arm-kernel@...ts.infradead.org, linux-pci@...r.kernel.org, 
	linux-kselftest@...r.kernel.org, imx@...ts.linux.dev, devicetree@...r.kernel.org
Subject: Re: [PATCH v19 01/10] PCI: endpoint: Set ID and of_node for function
 driver

On Wed, Jul 02, 2025 at 10:40:53AM GMT, Frank Li wrote:
> On Wed, Jul 02, 2025 at 04:30:48PM +0530, Manivannan Sadhasivam wrote:
> > On Mon, Jun 09, 2025 at 12:34:13PM GMT, Frank Li wrote:
> > > Set device ID as 'vfunc_no << 3 | func_no' and use
> > > 'device_set_of_node_from_dev()' to set 'of_node' the same as the EPC parent
> > > device.
> > >
> > > Currently, EPF 'of_node' is NULL, but many functions depend on 'of_node'
> > > settings, such as DMA, IOMMU, and MSI. At present, all DMA allocation
> > > functions use the EPC's device node, but they should use the EPF one.
> > > For multiple function drivers, IOMMU/MSI should be different for each
> > > function driver.
> > >
> >
> > We don't define OF node for any function, so device_set_of_node_from_dev() also
> > ends up reusing the EPC node. So how can you make use of it in multi EPF setup?
> 
> In mfd devices, children devices reuse parent's of_node
> drivers/gpio/gpio-adp5585.c
> drivers/input/keyboard/adp5589-keys.c
> drivers/pwm/pwm-adp5585.c
> 
> multi EPF should be similar to create multi children devices of mfd.
> 

No, they are not similar. MFD are real physical devices, but EPFs are (so far)
software based entities.

> > I don't understand.
> 
> >
> > > If multiple function devices share the same EPC device, there will be
> > > no isolation between them. Setting the ID and 'of_node' prepares for
> > > proper support.
> 
> Only share the same of_node.
> 
> Actually pci host bridge have similar situation, all pci ep devices reuse
> bridge's of node. framework use rid to distringuish it. EPF can use device::id
> to do similar things.
> 
> Actually iommu face the similar problem. So far, there are not EP device enable
> iommu yet, because it needs special mapping.
> 
> Prevously, I consider create dymatic of_node for each EPF and copy iommu/msi
> information to each children. But when I see adp5585 case, I think direct
> use parent's of_node should be simple and good enough.
> 
> In future, I suggest add children dt binding for it. For example: EPF provide
> a mailbox interface. how other dts node to refer to this mailbox's phandle?
> 

As I said above, EPFs are not real devices. There is currently only one
exception, MHI, which is backed by a hardware entity. So we cannot add
devicetree nodes for EPF, unless each EPF is a hardware entity.

- Mani

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