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

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Message-ID: <BY5PR11MB4306A066509DC8CB2ECEC164FDEDA@BY5PR11MB4306.namprd11.prod.outlook.com>
Date:   Fri, 8 Sep 2023 13:40:13 +0000
From:   "D M, Sharath Kumar" <sharath.kumar.d.m@...el.com>
To:     Bjorn Helgaas <helgaas@...nel.org>
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



> -----Original Message-----
> From: Bjorn Helgaas <helgaas@...nel.org>
> Sent: Friday, September 8, 2023 6:14 PM
> To: D M, Sharath Kumar <sharath.kumar.d.m@...el.com>
> Cc: lpieralisi@...nel.org; kw@...ux.com; robh@...nel.org;
> bhelgaas@...gle.com; linux-pci@...r.kernel.org; dinguyen@...nel.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 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
> > > > +static int _altera_pcie_cfg_read(struct altera_pcie *pcie, u8 busno,
> > > > +				 unsigned int devfn, int where, int size,
> > > > +				 u32 *value)
> > > > +{
> > > > +	if (busno == pcie->root_bus_nr && pcie->pcie_data->ops-
> > > >rp_read_cfg)
> > > > +		return pcie->pcie_data->ops->rp_read_cfg(pcie, busno,
> > > devfn,
> > > > +							where, size, value);
> > > > +
> > > > +	if (pcie->pcie_data->ops->ep_read_cfg)
> > > > +		return pcie->pcie_data->ops->ep_read_cfg(pcie, busno,
> > > devfn,
> > > > +							where, size, value);
> > > > +	return PCIBIOS_FUNC_NOT_SUPPORTED; }