linux-kernel - Re: [PATCH v9 2/7] PCI: dwc: Rename cpu_addr to parent_bus

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Message-ID: <Z64XrD2a5iHmLyRM@lizhi-Precision-Tower-5810>
Date: Thu, 13 Feb 2025 11:02:52 -0500
From: Frank Li <Frank.li@....com>
To: Bjorn Helgaas <helgaas@...nel.org>
Cc: Rob Herring <robh@...nel.org>, Saravana Kannan <saravanak@...gle.com>,
	Jingoo Han <jingoohan1@...il.com>,
	Manivannan Sadhasivam <manivannan.sadhasivam@...aro.org>,
	Lorenzo Pieralisi <lpieralisi@...nel.org>,
	Krzysztof Wilczyński <kw@...ux.com>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Richard Zhu <hongxing.zhu@....com>,
	Lucas Stach <l.stach@...gutronix.de>,
	Shawn Guo <shawnguo@...nel.org>,
	Sascha Hauer <s.hauer@...gutronix.de>,
	Pengutronix Kernel Team <kernel@...gutronix.de>,
	Fabio Estevam <festevam@...il.com>, devicetree@...r.kernel.org,
	linux-kernel@...r.kernel.org, linux-pci@...r.kernel.org,
	linux-arm-kernel@...ts.infradead.org, imx@...ts.linux.dev,
	Niklas Cassel <cassel@...nel.org>
Subject: Re: [PATCH v9 2/7] PCI: dwc: Rename cpu_addr to parent_bus_addr for
 ATU configuration

On Thu, Jan 30, 2025 at 11:02:06AM -0500, Frank Li wrote:
> On Wed, Jan 29, 2025 at 05:23:50PM -0600, Bjorn Helgaas wrote:
> > On Tue, Jan 28, 2025 at 05:07:35PM -0500, Frank Li wrote:
> > > Rename `cpu_addr` to `parent_bus_addr` in the DesignWare ATU configuration.
> > > The ATU translates parent bus addresses to PCI addresses, which are often
> > > the same as CPU addresses but can differ in systems where the bus fabric
> > > translates addresses before passing them to the PCIe controller. This
> > > renaming clarifies the purpose and avoids confusion.
> >
> > Based on dw_pcie_ep_inbound_atu() below, I guess the ATU can also
> > translate PCI addresses from incoming DMA to parent bus addresses?
>
> Yes, but root complex don't use it. Only EP use it. because most PCI root
> complex system doesn't transfer incoming address, which generally use iommu
> to do that. Linux already allow a simple map by use dt's dma-ranges and dma
> API already handle it.
>
> previous 'cpu_addr' is actually 'dma_bus_addr'.
>
> >
> > It's worth noting here that this patch only renames the member, and
> > IIUC, parent_bus_addr still incorrectly contains CPU physical
> > addresses.
>
> Anyway, call 'cpu_addr' for dw_pcie_ep_inbound_atu is wrong. Only one place
> call dw_pcie_ep_inbound_atu(), that's dw_pcie_ep_set_bar(), which use
> epf_bar->phys_addr, I think name 'phys_addr' is okay because most case it
> is refer to dma address space.

Bjoin:
	Do you any concern/comments about my reply?  how to move forward?
keep old cpu_addr or rename to parent_bus_addr, or futher work need be done.

Frank

>
> Frank
> >
> > > +++ b/drivers/pci/controller/dwc/pcie-designware-ep.c
> > > @@ -128,7 +128,7 @@ static int dw_pcie_ep_write_header(struct pci_epc *epc, u8 func_no, u8 vfunc_no,
> > >  }
> > >
> > >  static int dw_pcie_ep_inbound_atu(struct dw_pcie_ep *ep, u8 func_no, int type,
> > > -				  dma_addr_t cpu_addr, enum pci_barno bar,
> > > +				  dma_addr_t parent_bus_addr, enum pci_barno bar,
> > >  				  size_t size)