linux-kernel - Re: [PATCH v2 1/2] PCI: altera: refactor driver for supporting new platform

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Message-ID: <20230908195242.GA304243@bhelgaas>
Date:   Fri, 8 Sep 2023 14:52:42 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     "D M, Sharath Kumar" <sharath.kumar.d.m@...el.com>
Cc:     "lpieralisi@...nel.org" <lpieralisi@...nel.org>,
        "kw@...ux.com" <kw@...ux.com>, "robh@...nel.org" <robh@...nel.org>,
        "bhelgaas@...gle.com" <bhelgaas@...gle.com>,
        "linux-pci@...r.kernel.org" <linux-pci@...r.kernel.org>,
        "dinguyen@...nel.org" <dinguyen@...nel.org>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2 1/2] PCI: altera: refactor driver for supporting new
 platform

On Fri, Sep 08, 2023 at 01:40:13PM +0000, D M, Sharath Kumar wrote:
> > -----Original Message-----
> > From: Bjorn Helgaas <helgaas@...nel.org>
> > On Fri, Sep 08, 2023 at 09:09:34AM +0000, D M, Sharath Kumar wrote:
> > > > -----Original Message-----
> > > > From: Bjorn Helgaas <helgaas@...nel.org> ...
> > 
> > > > > +	int (*ep_read_cfg)(struct altera_pcie *pcie, u8 busno,
> > > > > +			unsigned int devfn, int where, int size, u32 *value);
> > > > > +	int (*ep_write_cfg)(struct altera_pcie *pcie, u8 busno,
> > > > > +			unsigned int devfn, int where, int size, u32 value);
> > > >
> > > > "ep_read_cfg" isn't the ideal name because it suggests "endpoint",
> > > > but it may be either an endpoint or a switch upstream port.  The
> > > > rockchip driver uses "other", which isn't super descriptive either but
> > might be better.
> > > >
> > > Ok will change to "nonrp_read_cfg" ?
> > 
> > I think the important point is not whether it's a Root Port or not, but whether
> > it's on the root *bus* or not.  In other words, I think the driver has to
> > determine whether to generate a Type 0 (targeting something on the root
> > bus) or a Type 1 (targeting something below a
> > bridge) config transaction (see PCI-to-PCI Bridge spec r1.2, sec 3.1.2.1).
> > 
> > There can be non-Root Ports on the root bus, so "nonrp" doesn't seem quite
> > right.  "Other" would be OK, since that's already used by other drivers.
> > Maybe "type0" and "type1" would be better and would fit well with the
> > root_bus_nr check you use to distinguish them?
> > 
> Situation is
> Root port configuration space  - memory mapped
> Non root port configuration space - indirect access/proprietary access
>     Type 0 for devices directly connected to root port
>     Type 1 for others

"mm", "ind"?