linux-kernel - Re: [PATCH v12 2/6] PCI: mediatek: Add new method to get shared pcie-cfg base address

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Message-ID: <20210830214317.GA27606@bjorn-Precision-5520>
Date:   Mon, 30 Aug 2021 16:43:17 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Chuanjia Liu <chuanjia.liu@...iatek.com>
Cc:     robh+dt@...nel.org, bhelgaas@...gle.com, matthias.bgg@...il.com,
        lorenzo.pieralisi@....com, ryder.lee@...iatek.com,
        jianjun.wang@...iatek.com, yong.wu@...iatek.com,
        linux-pci@...r.kernel.org, linux-mediatek@...ts.infradead.org,
        devicetree@...r.kernel.org, linux-arm-kernel@...ts.infradead.org,
        linux-kernel@...r.kernel.org
Subject: Re: [PATCH v12 2/6] PCI: mediatek: Add new method to get shared
 pcie-cfg base address

On Mon, Aug 30, 2021 at 03:09:44PM +0800, Chuanjia Liu wrote:
> On Fri, 2021-08-27 at 11:46 -0500, Bjorn Helgaas wrote:
> > On Mon, Aug 23, 2021 at 11:27:56AM +0800, Chuanjia Liu wrote:

> > > @@ -995,6 +1004,14 @@ static int mtk_pcie_subsys_powerup(struct
> > > mtk_pcie *pcie)
> > >  			return PTR_ERR(pcie->base);
> > >  	}
> > >  
> > > +	cfg_node = of_find_compatible_node(NULL, NULL,
> > > +					   "mediatek,generic-pciecfg");
> > > +	if (cfg_node) {
> > > +		pcie->cfg = syscon_node_to_regmap(cfg_node);
> > 
> > Other drivers in drivers/pci/controller/ use
> > syscon_regmap_lookup_by_phandle() (j721e, dra7xx, keystone,
> > layerscape, artpec6) or syscon_regmap_lookup_by_compatible() (imx6,
> > kirin, v3-semi).
> > 
> > You should do it the same way unless there's a need to be different.
>
> I have used phandle, but Rob suggested to search for the node by 
> compatible.

> The reason why syscon_regmap_lookup_by_compatible() is not 
> used here is that the pciecfg node is optional, and there is no need to
> return error when the node is not searched.

How about this?

  regmap = syscon_regmap_lookup_by_compatible("mediatek,generic-pciecfg");
  if (!IS_ERR(regmap))
    pcie->cfg = regmap;